Electronics

MJ wireless experiment in 1992

2011-03-31T04:41:00.000-07:00

2SJ113/2SK399 SEPP AB-40W stereo power amplifier, no feedback, the DC system

MOS-FET power output stage, a simple voltage・Miller called the NFB minor loops in multiplied by a powerful, and put on overalls with the NFB, has achieved very low output impedance, the natural sound of the amplifier.Lead chassis S4 (300 × 200 × 60) is used. Both sides in the handmade SHIMASHITA wood paneling.

Block on the chassis are amplified voltage capacitors and a small stage for those who for the power transformer and the radiator and looks imposing, but the real thing is compact and lightweight.

Input terminals and output terminals to a lot of effort SUPATORON.At the bottom of the radiator board SHI MOS-FET power output stage and to shorten the wiring, the gate RENAKU series resistance does not even oscillation.

Just change a little wiring, the source follower circuit voltage circuits in the mirror can be changed.
Miller-voltage operating conditions of the basic design is satisfactory, the source follower to change to get high-quality sound.

USB DAC GC-PCM2706

2011-03-31T04:26:00.000-07:00

USB DAC GC-PCM2706

As General of the computer sound card if the total effect is generally not very good, often wear headphones to listen to a lot of strange sounds, if you want to do-it-yourself USB DAC to make best results, a USB PCM2702 DAC chip, such as the PCM2706 and ...
I had the choice of PCM 2706PJT, the use of its flexible than the PCM2702, and SPDIF output can I2S, IT is a monster, was the only word regarded as a fundamental element of the PCM2706 to say whether the voice of their own if Otherwise, leave a fiberglass production that we have received and then the GC-CAD V2.0 are very good. I want to strengthen the function, right! Try it! However, as a result of recent time is not enough, I do not have the full demand Zhanyou added, only the strengthening of the next.
Plus BNC coaxial output, the Council received a suspension of the BNC. An increase in external power options, USB-General CAD is the use of USB directly to 5V power supply, but by the power of PC audio equipment may not always have the desired effect, I 'I am therefore of its external power supply, 3.3 V for the group 2 Power Supplies, a group of analog circuits for power, a group of digital circuits for power. COUNCIL PC and the lay-out discussion about the separation and a broken left on the hole, if you do not need external power, provided that it is broken, you can lower the volume.
The use of an external power L1117-3, the LDO 3V (voltage regulator IC), which is characterized by a low pressure difference, but only the best input voltage in the range of 4.8 to 6V, or I would during the process , The use of 12V DC adapter, power burn-L1117 at 3.3 V, burned on the exchange, burnt 7, the station is really great articles I bars.
The use of internal or external USB power to the circuit board to select Jumper, connect an external power supply for the employment of 1, 2, 2, 3 inserted in the internal use of USB power.
External power supply circuit left socket adapter, I had to stay 2 position, which one of you must also use their own elections in this direction for inserting the plug.
Fiber output can be used for the first TOTX178, 179,173, etc., fiber or compatible output of the first, I let you all types of electronic circuits in the first fiber-optic pin-compatible.
BNC BNC coaxial output is not directly in the main LAYOUT circuit board, I went to 2-pin, and then to people who can put on the chassis from outside the BNC or RCA Block.
As for the PCM2706 own production, I used the usual 3.5 mm headphone jack, if the direct use of computer speakers would be more practical, but it would be better received their best amplifiers.

Parts list is as follows:
R1, R2 ................................................ 15 Ω
R3, R4 ................................................ 22 Ω
R5, R6, R7, R8 ........................................ 3.3K
R9 .................................................... 1M
R10, R11 .............................................. 1.5K
R12, R13 .............................................. 330 Ω
R14 ................................................... 100 Ω

C1, C2, C3, C4 ........................................ 1uF/16V
C5,C6 C5, C6 .......................................... 47uF/16V
C7, C8 ................................................ 0.022uF (223)
C9, C10 ............................................... 100uF/16V
C11, C12 .............................................. 27P
C13 ................................................... 0.1uF grass-roots

U1 .................................................... PCM2706PJT
U2 .................................................... TOTX178 or compatible, and so on

LED ................................................... 3mmLED
L1, L2 ................................................ BEAD (core)
S1 ~ S7 ............................................... Small button switch
J1 .................................................... 3.5MM stereo headphone jack
J2 .................................................... USB-B-type outlet
CON1 .................................................. 2PIN pin Block
XTAL1 ................................................. Crystal 12Mhz
JP1, JP2 .............................................. 3PIN pin Block

Parts of the following non-necessary items, the use of an external power supply when the need for the following parts:
C14, C16, C18 ......................................... 100uF/16V
C15, C17 .............................................. 0.1uF grass-roots
P1 .................................................... 2.0mmDC Power Block
U3, U4 ................................................ L1117-3.3V

Due to the use of two-panel design, so even if you have to DIY circuit board, to be careful on the hole well, in the welding must also pay attention to board up and down side through the hole to connect, it is necessary to carefully, one by one spot , The top hole through the use of the welding I am fine copper (from the general removed the suspicious wire to the more than OK fine line), the first place through the hole and then welding, if there are places that hole capacitor, such as the outlet can not be double-sided The welding parts, but also to use such a lead through the first, in front of the hole to find places to foil next to the weld can not play other parts had to hole-blocking, if that hole is the resistance, the switch , And so on .. core, it can be a double-sided welding. If the plant is the system board, then of course there will be no hole through the problem.
In fact, such a small cost to achieve External computer audio, CP is a very high value, do not want to spend a lot of money, you want to burn the little DIY, can be said to be a good choice.
If you download the PDF file is in the next few pages, you can see the film circuit board files, printed automatically canceled when the zoom function to print 1:1.

Download PDF version: GC-PCM2706USBDAC-FL.pdf
Film file to download: PCM2706D-BL.pdf

Super Power Amplifier using TDA7250

2011-03-31T04:00:00.000-07:00

Super Power Amplifier using TDA7250

This 2-channel hybrid IC is normally configured with TIP142/147 power darlingtons for its' output. For those who prefer to use power transistors instead, the TDA7250 can easily be converted. All that is required are a few transistors, 4 additional resistors and some rewiring.
This conversion centers mainly on changing the output section to a Sziklai. In our IA502 on the right, drivers Q1,Q2 are 2SC2238 and 2SA968, and outputs Q5,Q6 are 2SA1216 and 2SC2922 respectively.
No instability problems were encountered from this conversion. After a period of run-in, the amplifier remained thermally stable.
Is this version worth the extra cost and effort?
If one is only interested in something basic, the TIP version would be sufficient. But if one is after sonic performance, I would recommend this version.

3 W FM TRANSMITTER

2011-03-26T07:30:00.000-07:00

3 W FM TRANSMITTER

Part
R1,R4,R14,R15 - 4 - 10K 1/4W Resistor
R2,R3 - 2 - 22K 1/4W Resistor
R5,R13 - 2 - 3.9K 1/4W Resistor
R6,R11 - 2 - 680 Ohm 1/4W Resistor
R7 - 1 - 150 Ohm 1/4W Resistor
R8,R12 - 2 - 100 Ohm 1/4W Resistor
R9 - 1 - 68 Ohm 1/4W Resistor
R10 - 1 - 6.8K 1/4W Resistor
C1 - 1 - 4.7pF Ceramic Disc Capacitor
C2,C3,C4,C5,C7,C11,C12 - 7 - 100nF Ceramic Disc Capacitor
C6,C9,C10 - 3 - 10nF Ceramic Disc Capacitor
C8,C14 - 2- 60pF Trimmer Capacitor
C13 - 1 - 82pF Ceramic Disc Capacitor
C15 - 1- 27pF Ceramic Disc Capacitor
C16 - 1- 22pF Ceramic Disc Capacitor
C17 - 1 - 10uF 25V Electrolytic Capacitor
C18 - 1 - 33pF Ceramic Disc Capacitor
C19 - 1 - 18pF Ceramic Disc Capacitor
C20 - 1 - 12pF Ceramic Disc Capacitor
C21,C22,C23,C24 - 4 - 40pF Trimmer Capacitor
C25 - 1 - 5pF Ceramic Disc Capacitor
L1 - 1 - 5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L2,L3,L5,L7,L9 - 5 - 6-hole Ferroxcube Wide band HF Choke (5 WDG)
L4,L6,L8 - 3 - 1.5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L10 - 1 - 8 WDG, Dia 5 mm, 1 mm CuAg, Space 1 mm
D1 - 1 - BB405 BB102 or equal (most varicaps with C = 2-20 pF [approx.] will do)
Q1 - 1 - 2N3866
Q2,Q4 - 2 - 2N2219A
Q3 - 1 - BF115
Q5 - 1 - 2N3553
U1 - 1 - 7810 Regulator
MIC -1- Electret Microphone
MISC - 1 - PC Board, Wire For Antenna, Heatsinks

BOSTER FM 30 Watt

2011-03-26T06:53:00.000-07:00

BOSTER FM 30 Watt

PARTS

C1, C2, C3, C4 = 10 -80pF
C 5 = 10nF
C6 = 1000pF
C7 = 100nF
C8 = 2200mF/35V
L1 = 1 coil with diameter of 10 mms, 1 mm
L2 = 7 coils with diameter of 10 mms, 0,8 mm
L3 = 3 coils with diameter of 10 mms, 1 mm
TR1 = BLY89
RFC = RF tsok
Download : pcb Linear FM 30Watt

4 W FM TRANSMITTER

2011-03-26T06:41:00.000-07:00

4 W FM TRANSMITTER

This is a small but quite powerful FM transmitter having three RF stages incorporating an audio preamplifier for better modulation. t has an output power of 4 Watts and works off 12-18 VDC which makes it easily portable. It is the ideal project for the beginner who wishes to get started in the fascinating world of FM broadcasting and wants a good basic circuit to experiment with.
Modulation type: ........ FM
Frequency range: .... 88-108 MHz
Working voltage: ..... 12-18 VDC
Maximum current: ....... 450 mA
Output power: ............ 4 W
Parts List

R1 = 220K
R2 = 4,7K
R3 = R4 = 10K
R5 = 82 Ohm
R = 150Ohm 1/2W x2 *
VR1 = 22K trimmer

C1 = C2 = 4,7uF 25V electrolytic
C3 = C13 = 4,7nF ceramic
C4 = C14 = 1nF ceramic
C5 = C6 = 470pF ceramic
C7 = 11pF ceramic
C8 = 3-10pF trimmer
C9 = C12 = 7-35pF trimmer
C10 = C11 = 10-60pF trimmer
C15 = 4-20pF trimmer
C16 = 22nF ceramic *

L1 = 4 turns of silver coated wire at 5,5mm diameter
L2 = 6 turns of silver coated wire at 5,5mm diameter
L3 = 3 turns of silver coated wire at 5,5mm diameter
L4 = printed on PCB
L5 = 5 turns of silver coated wire at 7,5mm diameter

RFC1=RFC2=RFC3= VK200 RFC tsok

TR1 = TR2 = 2N2219 NPN
TR3 = 2N3553 NPN
TR4 = BC547/BC548 NPN
D1 = 1N4148 diode *
MIC = crystalic microphone

FM TRANSMITTER 0,4 W

2011-03-26T06:31:00.000-07:00

FM TRANSMITTER 0,4 W

Parts list

Capacitors:
C1, C2, C12 - 100 pF (ceramic)
C3, C5 - 0,22 uF (electrolytic)
C4 - 1,8 nF (plastic)
C13, C16, C17, C19 - 1 nF (ceramic)
C8, C9 - 10 pF (ceramic)
C10 - 47 pF (ceramic)
C11 - 8,2 pF (ceramic)
C14 - 60 pF trimmer
C15 - 35 pF trimmer
C18, C7 - 100 nF (ceramic)
C20 - 470 uF (electrolytic, 16 V)

Coils:
(All coils are free-standing air-core types, wound of 0,7 mm Cu wire, 6 mm internal diameter.)
L1 - 4,5 coils
L2 - 9,5 coils
L3 - 4,5 coils

Resistors:
R1, R2 - 10 k pot.
R3 - 33 k
R4, R7, R12 - 10 k
R5, R11 - 470
R6 - 27 k
R8 - 22 k
R9 - 270
R10 - 100

Misc.:
D1 - BB409 (BB109G, BBY31) varicap
T1 - BC547C (BC548C, BC547B)
T2 - BFR91A (BFR96)
T3 - BFR96

Antenna
Power supply
3,5 mm jack
CD player, computer
6 V / 0,1 A bulb

PLL FM TRANSMITTER 1W

2011-03-24T02:51:00.000-07:00

PLL FM TRANSMITTER 1W

This small FM transmitter includes a limiter, a microphone amplifier and a PLL digital tuning. All the parts are placed on one circuit board. The RF power is switchable between 1 W (HI) and 0,2 W (LO).
Technical specifications
Supply voltage: 12 V from accumulator or regulated power supply
Supply current (HI/LO): 270/170 mA
RF power HI: 1 W
RF power LO: 0,2 W
Impedance: 50-75 ohm
Frequency range: 87,5-108 MHz
Modulation type: wide-band FM
Modulation inputs: line, mic, RDS/MPX
PCB dimensions: 11,3 x 8,8 cm

Radio Frequency

2011-03-24T02:46:00.000-07:00

Resistors:

R1 - pot. 5 k
R2, R12 - 1 k
R3 - 220
R4, R8, R10 - 27 k
R5, R6, R14, R17 - 10 k
R7, R16 - 470
R9 - 100
R11 - 270
R13 - 10
R15 - 22 k

Capacitors:
C1 - 4,7 uF
C2 - 1 uF
C3, C4, C12 - 100 pF
C6, C9, C11, C13, C14, C19, C22 - 1 nF
C7, C8 - 10 pF
C10 - 8.2 pF
C18 - 22 pF
C15 - trimmer 47 pF
C16, C17 - trimmer 60 pF
C20, C5 - 100 nF mini
C23 - 470 uF

Coils:
(All coils are free-standing air-core types, wound of 0,7 mm Cu wire, 6 mm internal diameter.)
L1 - 4,5 coils
L3 - 2,5 coils
L4 - 1,5 coils
L2 - 6,5 coils around R9 resistor
L5 - 9,5 coils
L6 - 5,5 coils
L7 - 3,5 coils

Diodes:
D1, D2 - BB109G, BBY31 or BB409

Transistors:
T1 - BC547C (BC548C, BC547B)
T2 - BFR91A (BFR96)
T3 - BFR96
T4 - 2SC1971

Misc:
S1 - switch

PLL digital tuning

2011-03-24T02:43:00.000-07:00

PLL digital tuning

Resistors:
R31 - 1k
R32 - 4k7
R33, R37 - 10k
R34, R35 - 1k
R36 - 470
R38 - 47k

Capacitors:
C31, C42 - 2,2 nF
C32, C40 - 10 nF
C33 - 47 uF
C34 - 10 uF tantal
C35 - 0,47 uF
C36, C41 - 100 nF
C37 - 1 nF
C38 - 220 uF
C39 - 22 pF

Misc:
IC31 - SAA1057
IC32 - PIC16F84-04 + socket
IC33 - 78L05
X31 - 4 MHz crystal
D31 - LED diode
Tl31 - button
Jumpers 2x8 pins or DIP switches

Audio and power supply part

2011-03-24T02:36:00.000-07:00

Audio and power supply part

Resistors:
R51, R52 - pot. 5 k
R53, R58, R64 - 10 k
R54, R55 - 22 k
R56 - 56 k
R57 - 1,5 k
R59 - 180 k
R60 - 820
R61 - 10 M
R62 - 47
R63 - 240 k

Capacitors:
C51, C54 - 100 pF
C52, C57 - 2,2 uF
C53 - 1 uF
C55, C62, C63 - 10 uF
C56, C64 - 47 nF
C58 - 1 nF plastic
C59, C60 - 1 uF tantal 25 V
C61 - 100 uF
C65 - 150 nF
C66, C67, C68, C70 - 10 nF
C69 - 470 uF

Misc:
T51 - BF245C
T52 - BC556B
IC51, IC52 - LM386
S51 - switch

Complete parts list

Resistors:
1x 10
1x 47
1x 100
1x 270
2x 220
3x 470
1x 820
5x 1k
1x 1,5 k
1x 4,7 k
9x 10 k
3x 22 k
3x 27 k
1x 56 k
1x 47 k
1x 180 k
1x 240 k
1x 10 M
3x pot. 5 k log.

Capacitors:
1x 8,2 pF
2x 10 pF
3x 22 pF
5x 100 pF
8x 1 nF
1x 1 nF plastic
2x 2,2 nF
5x 10 nF
2x 47 nF
4x 100 nF mini
1x 150 nF
1x 0,47 uF
2x 1 uF
2x 2,2 uF
1x 4,7 uF
4x 10 uF
1x 47 uF
1x 100 uF
1x 220 uF
2x 470 uF
2x 1 uF tantal
1x 10 uF tantal
1x trimmer 47 pF
2x trimmer 60 pF

Semiconductors:
1x BC547C (BC548C, BC547B)
1x BFR91A
1x BFR96
1x 2SC1971
1x BC556B
1x BF245C
2x LM386
1x SAA1057
1x PIC16F84A-04 + socket
1x 78L05
1x Yellow LED 3 mm
2x BB109G, BBY31 or BB409
Misc:
1x 4 MHz crystal
2x switch
1x button
1x jumpers 2x8 pins or DIP switches
1x power supply connector
3x jack 3,5 mm
1x antenna connector
1x plastic case
thin shielded cables

MINIATURE FM TRANSMITTER

2011-03-24T02:10:00.000-07:00

MINIATURE FM TRANSMITTER

R1,R4,R6 = 10K C1,C2 = 0.1uF Q1,Q2 = 2N3904
R2 = 1M C3 = 0.01uF L1 = 0.1uH
R3 = 100K C4 = 4-40pF
R5 = 100 ohm C5 = 4.7pF
R7 = 1K

Construction
This miniature transmitter is easy to construct and it's transmissions can be picked up on any standard FM radio. It has a range of up to 1/4-mile (400 meters) or more, depending on the line-of-sight, obstructions by large buildings, etc. It is great for room monitoring, baby listening, nature research, etc.
L1 is 8 to 10 turns of 22 gauge hookup wire close wound around a non-conductive 1/4-inch diameter form, such as a pencil.
C4 is a small, screw-adjustable, trimmer capacitor.
Set your FM radio for a clear, black space in the lower end of the band (88MHz). Then, with a non-metallic/non-conductive trimmer tool, adjust this capacitor for the clearest reception. A little experimenting and patience may be in order.
Most of the parts values are not critical, so you can try adjusting them to see what happens.
If you decide to substitute transistors with something similar you already have, it maybe necessary adjust the collector voltage of Q1 by changing the value of R2 or R3 (because you change transistors, it changes this bias on the base of Q1). It should be about 1/2 the supply voltage (about 4 or 5v).

Notes
The default for the capacitors type is ceramic, preferably the npo 1% (low noise) type or equivalent. But basically nothing critical here. Use any capacitor you have laying around, but NO electrolytic or tantalum caps. Only if you intend to use this circuit outside the home you may want to select more temperature stable capacitors.
To find the signal on your receiver, make sure there is a signal coming into the microphone, otherwise the circuit won't work. I use an old mechanical alarm clock (you know, with those two large bells on it). I put this clock by the microphone which picks up the loud tick-tock. I'm sure you get the idea... Or you can just lightly tap the microphone while searching for the location of the signal on your receiver.

USB DAC GC-PCM2706

2010-10-16T04:00:00.000-07:00

I had the choice of PCM 2706PJT, the use of its flexible than the PCM2702, and SPDIF output can I2S, IT is a monster, was the only word regarded as a fundamental element of the PCM2706 to say whether the voice of their own if Otherwise, leave a fiberglass production that we have received and then the GC-CAD V2.0 are very good. I want to strengthen the function, right! Try it! However, as a result of recent time is not enough, I do not have the full demand Zhanyou added, only the strengthening of the next.
1.Plus BNC coaxial output, the Council received a suspension of the BNC.
2.An increase in external power options, USB-General CAD is the use of USB directly to 5V power supply, but by the power of PC audio equipment may not always have the desired effect, I 'I am therefore of its external power supply, 3.3 V for the group 2 Power Supplies, a group of analog circuits for power, a group of digital circuits for power. COUNCIL PC and the lay-out discussion about the separation and a broken left on the hole, if you do not need external power, provided that it is broken, you can lower the volume.
The use of an external power L1117-3, the LDO 3V (voltage regulator IC), which is characterized by a low pressure difference, but only the best input voltage in the range of 4.8 to 6V, or I would during the process , The use of 12V DC adapter, power burn-L1117 at 3.3 V, burned on the exchange, burnt 7, the station is really great articles I bars.
The use of internal or external USB power to the circuit board to select Jumper, connect an external power supply for the employment of 1, 2, 2, 3 inserted in the internal use of USB power.
External power supply circuit left socket adapter, I had to stay 2 position, which one of you must also use their own elections in this direction for inserting the plug.
Fiber output can be used for the first TOTX178, 179,173, etc., fiber or compatible output of the first, I let you all types of electronic circuits in the first fiber-optic pin-compatible.
BNC BNC coaxial output is not directly in the main LAYOUT circuit board, I went to 2-pin, and then to people who can put on the chassis from outside the BNC or RCA Block.
As for the PCM2706 own production, I used the usual 3.5 mm headphone jack, if the direct use of computer speakers would be more practical, but it would be better received their best amplifiers.
Parts list is as follows:
R1, R2 ................................................ 15 Ω
R3, R4 ................................................ 22 Ω
R5, R6, R7, R8 ........................................ 3.3K
R9 .................................................... 1M
R10, R11 .............................................. 1.5K
R12, R13 .............................................. 330 Ω
R14 ................................................... 100 Ω
C1, C2, C3, C4 ........................................ 1uF/16V
C5,C6 C5, C6 .......................................... 47uF/16V
C7, C8 ................................................ 0.022uF (223)
C9, C10 ............................................... 100uF/16V
C11, C12 .............................................. 27P
C13 ................................................... 0.1uF grass-roots
U1 .................................................... PCM2706PJT
U2 .................................................... TOTX178 or compatible, and so on
LED ................................................... 3mmLED
L1, L2 ................................................ BEAD (core)
S1 ~ S7 ............................................... Small button switch
J1 .................................................... 3.5MM stereo headphone jack
J2 .................................................... USB-B-type outlet
CON1 .................................................. 2PIN pin Block
XTAL1 ................................................. Crystal 12Mhz
JP1, JP2 .............................................. 3PIN pin Block
Parts of the following non-necessary items, the use of an external power supply when the need for the following parts:
C14, C16, C18 ......................................... 100uF/16V
C15, C17 .............................................. 0.1uF grass-roots
P1 .................................................... 2.0mmDC Power Block
U3, U4 ................................................ L1117-3.3V

Audio and power supply part

2010-10-09T21:00:00.000-07:00

Audio and power supply part

Resistors:
R51, R52 - pot. 5 k, R53, R58, R64 - 10 k, R54, R55 - 22 k
R56 - 56 k, R57 - 1,5 k, R59 - 180 k, R60 - 820, R61 - 10 M
R62 - 47, R63 - 240 k

Capacitors:
C51, C54 - 100 pF, C52, C57 - 2,2 uF, C53 - 1 uF, C55, C62, C63 - 10 uF
C56, C64 - 47 nF, C58 - 1 nF plastic, C59, C60 - 1 uF tantal 25 V
C61 - 100 uF, C65 - 150 nF, C66, C67, C68, C70 - 10 nF, C69 - 470 uF

Misc:
T51 - BF245C
T52 - BC556B
IC51, IC52 - LM386
S51 - switch

Complete parts list

Resistors:
1x 10, 1x 47, 1x 100, 1x 270, 2x 220, 3x 470, 1x 820, 5x 1k
1x 1,5 k, 1x 4,7 k, 9x 10 k, 3x 22 k, 3x 27 k, 1x 56 k
1x 47 k, 1x 180 k, 1x 240 k, 1x 10 M, 3x pot. 5 k log.

Capacitors:
1x 8,2 pF, 2x 10 pF, 3x 22 pF, 5x 100 pF
8x 1 nF, 1x 1 nF plastic, 2x 2,2 nF, 5x 10 nF
2x 47 nF, 4x 100 nF mini, 1x 150 nF, 1x 0,47 uF
2x 1 uF, 2x 2,2 uF, 1x 4,7 uF, 4x 10 uF
1x 47 uF, 1x 100 uF, 1x 220 uF, 2x 470 uF
2x 1 uF tantal, 1x 10 uF tantal
1x trimmer 47 pF, 2x trimmer 60 pF

Semiconductors:
1x BC547C (BC548C, BC547B)
1x BFR91A
1x BFR96
1x 2SC1971
1x BC556B
1x BF245C
2x LM386
1x SAA1057
1x PIC16F84A-04 + socket
1x 78L05
1x Yellow LED 3 mm
2x BB109G, BBY31 or BB409

Misc:
1x 4 MHz crystal
2x switch
1x button
1x jumpers 2x8 pins or DIP switches
1x power supply connector
3x jack 3,5 mm
1x antenne connector
1x plastic case
thin shielded cables

Low-power amplifier APA4800

2010-09-29T09:46:00.000-07:00

Low-power amplifier APA4800 / APA480

Anpec APA4800/APA4801 is produced by SO-8 or DIP-8 Plastic Class A and B stereo audio amplifier IC, mainly used in portable digital audio, PC microphone and amplifier, and so on.
APA4800 drive with the stereo 290 mW, 8 Ω audio amplifier circuit as shown in Figure 1.
APA4800 built-in amplifier A and B, with its terminal phase (1 NA +, 1NB +) connected together and put 1 / 2 VDD reference voltage (VRFE). Power supply voltage range of 3 ~ 7 V, no-load supply current to 205 mA (VDD = 5V). Two input VINA, VINB the CiA, RiA and CiB, RiB separately applied to the amplifier A and B RP-INA-input and INB-, feet and two feet of output respectively by the COA and capacitive coupling COB RLA applied to the load and RLB. Link IC feet and legs and feet and ⑥ ⑦ feet of the CCA, RCA, and CCB, RCB A and B respectively, the frequency compensation components. Signal to noise ratio (S / N) of 100 dB, total harmonic distortion plus noise and signal ratio [(THD + N) / S] is 0.15% (typical) slew rate to 5 V / μ s, power supply ripple suppression Than (PSRR) of 55 dB, working temperature range of -40 ~ +85 ℃.
APA4801 used as a driver of 280 mW, 8 Ω stereo audio amplifier circuit shown in Figure 2.
APA4800 compared with, APA4801 integrated resistor divider, eliminating the external resistance. At the same time, APA4801 also has excellent noise-free adjustment of the function, and flexible regulation and noise-free switching Kata without sound. IC's Mute feet (feet) function is to control the importation of chips disability (disable). When Mute feet for the "H", the speaker movements for the "L", so that voices continue to weaken (Mute on). IC in the VDD = 5V and contained no power under the current IDD = 2.5mA, the standby current is only 150 μ A, Mute pin input voltage to 0.8 V, no noise attenuation adjustment (ATT) to 75 dB, (THD + N) S = 0. 1%, S / N = 100dB, slew rate to 5 V / μ s. In 10% (THD + N) into 8 Ω load on the output power of 280 mW; When RL = 16 Ω, the output power is 160 mW. Power supply ripple suppression (PSRR) = 76dB.
Amplifier input capacitance (CiA, CiB) circuit of the numerical impact of the low-frequency performance. If Ci and IC 130 k Ω resistance in the form of high-pass filter (HPF) inflection point for the frequency fc, while Ci = 1 / (2 π × 130k Ω × fC). In this circuit, Ci optional 1 μ F of the Ceramic capacitor.

Concise FET Audio Amplifiers

2010-09-21T17:38:00.000-07:00

Concise FET Audio Amplifiers

FET voltage control devices for its high-frequency characteristics, and as a tube amplifier tube-like sound. I have produced a partial negative feedback FET amplifier, the actual effect of listening is not satisfactory. Designed as a negative feedback loop amplifier, the sweet sounds markedly effective, treble detail, the intensity of the full bass, outstanding results.
Circuit principle as shown below, for a typical OCL amp. IC1-A for the input stage; BG1, BG2 incentive for the class; BG3, BG4 is composed of complementary MOSFET output level; IC1-B for the DC Circuit 0.1 Servo.
IC1-A voltage from the amplification, because of limited supply voltage, the level output signal range of not more than ± 15V, if the after-use of the radio output, output power too small.
The circuit is designed to play Yun-simple, excellent performance characteristics, but also meet the appropriate output power. Therefore, the power circuit from the two groups (± 15V, ± 36V) power supply, regulators ± 15V supply Yun-use, ± 36V supply after-use. BG1, BG2 for a total emitter circuit, R8, R9 for the negative feedback resistor, R1, R5, D1, D2, R18, R19 for BG1, BG2 provide a stable DC bias, in order to ensure its on-state, in addition to the same level Voltage amplification, the more important is to achieve a different power supply circuit signal coupling. FET voltage amplifier is the case, although the current drive did not specifically require, but to consider FET input capacitance of the characteristics of high-frequency.
Therefore, the resistance of the drive signal should be small enough. BG3, BG4 signal the driver were taken from the BG2, BG1 load R4, R3. BG1, BG2 the collector load resistance was divided into two sections, as the source of FET gate drive voltage should be no larger than 20 volts. BG3, BG4 for MOSFET on the composition of the drain output stage. R11, R12 for the source of negative feedback resistor. IC1-B's role is stable at the end of the mid-point of DC voltage, in order to achieve the DC amplifier. R13, R7 is a negative feedback loop resistance. R20, R21 to prevent the MOS high frequency of self-designed; C2, R16 role is to prevent self-circuit.

SAP15 use of the gallstone mixer amp

2010-09-21T17:21:00.000-07:00

SAP15 use of the gallstone mixer amp

This paper describes the gallstone mixer, the use of high-frequency dual-triode 6 N3 do audio amplification, a distortion of small, high-frequency response, and high conversion rate, the advantages of large dynamic range.
Power output level by the Japanese company is willing to three audio supervisor SAP15N / P, which is two complementary Darlington on the internal diodes with a bias. The tube also known as high-speed thermal reaction transistors, TRAITR tube, has high thermal stability.
Power output circuit for a typical OCL, and a constant current drive, SAP15N ② the first leg and foot SAP15P the ④ indirectly a 510 Ω potentiometers, for regulating the size of bias, thus adjusting the static-amp Current, the circuit of quiescent current 100 mA. Tube before class and after class between transistors by capacitive coupling.
Before a two-6 N3 respectively as voltage and power-driven zoom level, and then into SRPP circuit. To improve the performance of amplifiers, and the depth of the little negative feedback loop.
Using two power transformer power supply. A transformer capacity of 20 W, output DC 200 V, exchange of 6.3 V to 4 6 N3 tube power supply. Transformer can be used C-or E-core. Another transformer capacity should be more than 300 W, DC output voltage ± 45V, for transistor-level power amplifier.

Practical small amp

2010-09-18T00:38:00.000-07:00

Practical small amp

As player easy to carry, easy to operate, better sound quality and therefore were in favor of the school Philharmonic. However, players have adopted a low DC power supply (such as 1.5 V, 2V, 3V), the output power of small. I designed a special power output up to 1 W simple small amplifier, such as a loudness, noise reduction, volume and tone control, and other functions, and low cost, only 30 yuan. Its circuit schematics see at top.
Map, RL match for the resistance, and its value should be nominal load and players agreed to ensure that the player's output stage circuit work in the best working conditions. C3, C4, W2 and C1, C2, W1 are left and right channel and the volume control circuit, such as loudness, high-frequency noise and have a certain effect. R5 ~ R8, W5, W6, C9 ~ C12 and R1 ~ R4, W3, W4, C5 ~ C8 were a summary of the left and right channel tone control circuit. R13 ~ R16, C14 and R9 ~ R12, C13 respectively, a left and right channel noise reduction circuit and the simple low-pass filter, and the tone control circuit, and so clever with the TDA2822 can get the input of the record of similar signal Waveform, so that fidelity to improve. R18 and R20 output for the protection of resistance, because of output for the prevention of damage to short-circuit TDA2822. R22, LED1, LED2 composed of the circuit flow instructions, when the amplifier is greater than 400 mA operating current when, LED1 and LED2 will be luminous. C13 and C14 to enter straight at coupling capacitance, leakage should be the minimum quality of electrolytic capacitors, to facilitate smooth passage of audio signals, do not block signals. C17 and C18 to enter the playback of the access road, often in a typical circuit for 10 μ F or 47 μ F. Its input impedance is too large, would cause obstruction or signal from self-excited, here C17 and C18 will increase to 100 μ F, its quality has improved, the range broadens. C26 and C27 straight at the output coupling capacitance, usually choose to 220 μ F, this is too high output impedance, signal obstruction caused distortion, or even self-excited, C26 and C27 will now increase to 680 μ F, sound quality improved significantly, the range is wider.
The circuit as long as the correct installation, components of good quality and do not have to debug to work properly.

Seiko secret agents high-quality amp

2010-09-17T22:32:00.000-07:00

I use a switching power supply and production of high quality amp board a power amplifier was a friend of Baozou a hard lazy. Although the Dodgers in the side, but the general suspected of power too small, it is difficult to meet the dynamic needs of Baopeng programmes, in particular the relationship between several good friends to sing karaoke OK, not turning the big voice, frequently so that the output was only 10 Dodgers a few watts of serious overload distortion. So recently pick up the pieces produced a fine performance of the power amplifier.

First, the choice of amplifier circuits produced in the original amp (switching power supply, high-quality amplifier boards, circuit see Figure 1) on the basis of the set into the pitch, volume, balance and 3 D function in a high-quality audio circuit LM4610N ( Circuit see Figure 2) and substantially improve the clarity BBE music circuit XR1075, discard signal switch circuit. LM4610N electrical parameters are as follows: voltage to 9 V ~ 18V (typically for 12 V); distortion of 0.03 percent; SNR 80 dB; frequency response of 250 kHz; volume control 75 dB; balance adjustment 1 ~ 20 dB; pitch adjustment ± 15dB, The largest gain of 2 dB, while a 3 D sound field processing functions. XR1071 to chip at the core of the music circuit definition upgrade for the United States EXAR the company's second generation product, the performance is better than the first generation M2150 and Japan Roma's BA3884, its parameters: voltage ± 5V, enhance clarity of 0 ~ 9.7dB, bass upgrading of 0 ~ 9.9 dB, the circuit board components of the factory finished slightly out of choice.

Second, the specific production: the use of a power amplifier chassis scrapped the "ambitious" 250 W transistor amplifiers chassis, for all devices and removed all the panels, and the other by 3 mm thick aluminum plate in accordance with the mechanism of re-design panel request Processing. The chassis and slightly larger than the standard chassis, the size of 550 mm × 410mm × 145mm, just under the amplifier to accommodate all the circuits and components. Because of the modules are finished plate, it was only in accordance with circuit assembly when asked to make a simple connection, but must pay attention to the current channel should choose high-quality wire, and as far as possible be rough and short and to distinguish between different colors , And small current signal path also should try to select good quality and high capacity wires and signal lines. Signal from the input signal between the start of each board are connected by shielding and shielding net-line termination, to avoid induced noise. Machines that the unit should follow the grounding principle that the board first with stout ground wire (usually black) leads to one point after pooling in the case, the specific location of ground would be after repeated tests, which if done Well be the complete elimination of exchange of sound. As a reminder, most have finished circuit boards have a fixed holes, but there are 12 holes and is connected to power, such as not dealing with insulation, be fixed with screws in metal enclosure, often Formation of the multi-circuit grounding, is prone to lead the exchange sound, which is many enthusiasts in the production of audio and helpless when the source of noise. The correct approach is to use sharp blade ringing fixed holes, with the power ground wire separation, in order to achieve the purpose of that grounding. Because of the power amplifier circuit, as many as 67 units (transformers, switches, power supply), should be fully well the elements of metal and insulation between the floor and preventing earthquakes work. The author's approach is to use a 15 mm thick wooden boards (depending on the size of floor) tiles on the floor, then screw the plate with wooden floor and closely connected together, and then each circuit element Were fixed in the board. At a fixed switching power supply and power transformer before in his next to put the appropriate size of a car inner tubes, to eradicate due to shock arising from the adverse effects. Amp produced a success or not, with a level of quality of power supply has a close relationship. The audio amplifier for the two panels to provide power from one pair of exchanges of high-quality 16 V/35W E-type transformers bear, the 10 A/100V AC rectifier bridge rectifier, 2200 μ F/50V through the filter capacitance from 7812,7912 3 Regulators and NE5532-block composed of servo power regulator after two sound boards to use (see Figure 3 circuit), so high-quality power supply can LM4610N and the performance of XR1071 play to the limit. This amplifier production, give up the production amp commonly used when the connector-even, and the plate connections (including the power input, the amplifier output) are direct welding, such connection is bad and the connector could have been avoided because of the surface Oxidation caused by signal degradation and noise. assembly, with the multimeter DC voltage measurement amplifier block the mid-point of potential output, should generally be in the 100 mV below.

Third, the trial feelings: Listen, in order not to high-quality signal to cover up the shortcomings of the power amplifier, the first by the author of the JVC TD-W205 cassette blocks to the amp, access to a new two-frequency shelves Granville me. The first two sound boards function switch to pull "OFF" position, I found the amp to-noise ratio high, static, even if the speaker is also close to the ear can not hear any noise. Take a few genuine Yindai disk, the general feeling is that open-market, the balance of good, filled with bass, and Alto bright and clear, crisp and sweet treble is fine. Later, with a new Section 330 super VCD players will JVC TD-W205 deck replaced, take a few quite familiar with their first song, I feel high bass have different degrees of extension, and will XR1071 pull the switch to function "ON" Block, clarity and bass compensation for proper regulation, then obviously wide sound field, increase the density of music, much more clarity, and have heard some never before heard the message. Quite powerful bass, 3 D of the LM4610 will be switched on, with three-dimensional sound field and throughout the entire space, surrounded by a good sense, the trial several classic films, I feel very Guoyin.

2-Way Active Loudspeaker

2010-07-24T09:57:00.000-07:00

2-Way Active Loudspeaker

Active loudspeakers have a lot of advantages concerning simple loudspeakers that use passive components for the elements concretisation of segregation of frequencies. In the case of active loudspeakers we have, proportionally, bigger build cost, because each loudspeaker is led by his own power amplifier. In properly drawn active loudspeaker, the quality of sound is much better and the distortions very low, because it does not use inductors and large capacitors in the road of signal. All capacitors exist in the signal road, they have very small value and they are very good quality. This does not mean that one well drawn passive loudspeaker is not good, perhaps better than one active. On the contrary one active loudspeaker is enough difficult in the manufacture. In the [Fig.1], exist a circuit of 2-way active loudspeaker. As we see also in the Block diagram [Fig.2], exist one classic 2-way crossover with cross frequency fc=3100HZ [-24dB/oct]. This frequency was selected, because it is near in the cross frequency of many speakers of trade, it can however change and be adapted in your own speakers choice, its enough you use the types that give for calculation [Fig.3]. The IC1 makes the input adaptation, the filters round the IC2 creates a high-pass filter of frequencies, for frequencies above Fc=3100HZ, on the contrary the components round the IC3 creates a low-pass filter, for frequencies under 3100HZ. With the trimmer TR1 in the line of high frequencies we can adaptable, if it needs, the level between the two speakers. Usually it will need we lower at 10% the level tweeter concerning woofer. In a lot of points of filter exist capacitors and resistors that are not used, but are there for future changes, in a other cross frequency, as the R6 and R10 that are not used. To the next stage the two outputs of filter are drive to the two power amplifiers, the IC4 for the high frequencies and the IC5 for low. Those of are two hybrid IC by Sanyo, with output power 80W/8ohms, with very good characteristics and sound. It can become change with other type of series as STK4036, STK4038, STK4040, with proportional modification of power supply voltage. The particular line is used in enough active loudspeakers, with very good results. Good its used type STK4042XI, because it has more modern internal designing, concerning type STK404II. Filters RLF1-2 in the exit of amplifiers are constituted by resistor R27 or R38 and a inductor wounded round this, in three layers. The inductor is made with 25 until 30 coils of cupreous wire, diameter 1mm. In the amplifiers output exist the contacts of relay RL1, who is checked by the protection from DC and delay system. This circuit is found round the IC6 and works as follows: When the circuit is supplied exist a delay 5 sec in the connection speakers above in the amplifiers outputs, so that are not pass the charge capacitors noises. On the contrary when we break the power supply, then RL1 disconnect very fast the speakers from amplifiers, so that is not heard the discharge noise of capacitors. At the same time the circuit protects the speakers from DC voltages, that will be presented for any reason, in the output Of power amplifiers, opening the contacts of RL1 and disconnect, very fast the speakers. The circuit operation of protection/ delay becomes obvious from Led [D20], which should be placed in obvious point in the speakers box. The connections it appears in the Fig. 2. The transformer is toroidal, good quality. The main pcb, the heatsink, the transformer, the rectifier bridge BR1, as also all the components that appear except main pcb, are placed in a aluminium piece of suitable dimensions which is adapted in dimensions of the speakers box and is placed in the back side of box. Two power amplifiers IC4 and IC5 clinched above in the heatsink. The total performance of loudspeaker depends always from the characteristics of units Tweeter and Woofer, that will be used in this, also from the designing and the quality of the box. Older i used in the place tweeter the T33Α and woofer the B200G by KEF.

Part List
R1-21-32-25-36-58=1 Kohms C19-20-52=10uF 25V IC1=TL071
R2=47 Kohms C21-35=470pF IC2-3=TL072-NE5532
R3-4-5-7-8-9-46=22 Kohms C22-36=470nF 63V MKT IC4-5=SKT4042[XI] or [II]*See text
R6-10=N.C *See text C24-25-26-38-39-40=100pF IC6=4093
R11........18=22 Kohms C27-41=10pF IC7=7812T
R19-20=47 ohms C28-42=100nF 100V MKT IC8=7815T
R22-33=33 Kohms C29-43=1nF 63V MKT IC9=7915T
R23-24-34-35=100 ohms C30-34-44-48=100uF 63V RL1=Relay 12V [G2R2 Omron]
R26-37=0.22 ohms 5W C31-45=220uF 25V RLF1-2=*See text
R27-38=10 ohms 3W C32-33-46-47=10uF 63V F1-2-3-4=1.6A FAST 5X20mm
R28-39=6.8 ohms C49=47uF 25V F5=1A SLOW 5X20mm[Fig.2]
R29-40=12 Kohms C50-51=100nF 63V MKT T1=220V//A=2X30V 250VA

B=2X15V 30VA [Toroidal]
R30-41-53-54=10 Kohms C53=1uF 25V
R31-45=560 ohms C54=3.3uF 25V
R44-45=1 Mohms C55-56-58-59=33uF 63V JF1=3pin male supply jack
R47=39 Kohms C57-60=22uF 16V JF2=Female RCA Jack
R48-50=15 Kohms C61-62=15000uF 63V AXIAL J1-3=2pin conn. with 2.54mm pin step
R49-51-52-55=56 Kohms C63-64=2200uF 25V AXIAL J2=3pin conn. with 2.54mm pin step
R56-57=3.9 Kohms C65-66-67-68=100nF 63V MKT J4=3pin conn. with 3.96mm pin step
R43=470 ohms 1W Q1=BD679 J5=4pin conn. with 3.96mm pin step
TR1=47 Kohms trimmer horizontal Q2-3=BC550 T=Tweeter 8ohms 50 until 80W
C1-22-36-23-37=1uF 63V MKT D1-2-3-4=1N4002 W=Woofer 8ohms 50 until 100W
C2=390pF D5=8.2V 0.5W Zener BR1=Bridge rect. 400V 25A [Fig.2]* See text
C3-4-7-8-14-15=100nF 63V MKT D6=1N4148 BR2=Bridge rect. 100V 1.5A
C5-6-9-10-11-12=3.3nF 63V MKT* See text D7.....19=1N4148 All resistors is 0.5W 1% metal film except for announce differently
C13-16-17-18=3.3nF 63V MKT*See text D20=5mm LED [Fig.2]

SPECIFICATIONS
Input sensitivity 1.1Vrms
Input impedance 47K
Output Power (0.1% THD) 150W total
Frequency crossover 3100HZ
slope -24dB/oct

AVR AtMega8 Optical

2010-07-10T10:26:00.000-07:00

Stimmopped is AVR ATmega8-based project that will assists you in tuning your string instrument to a given tone. It utilizes the stroboscopic effect to give feedback about the adjustment of your instrument. When the frequency that you chose has tone then the two LEDs on the board blink. Two lines are projected at a fixed position on the string when the string vibrates with the correct frequency. If frequencies don't match, the lines appear to be blinking or moving to the observer's eye. The moving or blinking effect decreases with decreasing difference between the two frequencies.
"The project has two switches to choose the tone and instrument. Switch S1 toggles the current mode of the menu, which is either "choose instrument" or "choose tone". The 7-segment display displays the current selection. In the instrument selection mode, the display is lit up a bit brighter. Switch number two (S2) selects the tone or instrument in the given mode." said Madex (Martin), the designer.
DOWNLOAD : Source Code And Layout

PIC Serial Port Servo Controller

2010-07-10T10:14:00.000-07:00

PIC Serial Port Servo Controller

The PIC Based servo controller is a small project that allow you to control some robotics. The project uses a PIC16F84 microcontroller from Microchip to drive servo motors and digital outputs. It receives commands from a host computer via a standard RS232 serial interface.
To control the servos and outputs we need to send commands to the PIC. Some of the commands are single byte commands; some however require two bytes. The first byte always contains the command and the channel to which the command applies. We will call this the 'Command' byte. The second byte (when needed) will contain data for the command; we will call this the 'Data' byte and is used when we need to set the servo offset or position for example, said Ashley Roll, the designer.
The command byte is split into two nibbles (4 bits), the upper one defines the command to execute and the lower defines the channel (which servo or digital output) is to be affected.
DOWNLOAD : PIC program | Schematic

AVR Electronic Humidor

2010-07-06T12:12:00.000-07:00

This Humidor project was designed with a Peltier module and Sensirion SHT1X series sensors. The project built to keep cigars in perfect condition by maintain preferred level of moisture and keep the temperature around 70 degrees. The core of system is based on a microcontroller ATMEGA-16 programmed with BASCOM-AVR. The application is broken into two sections the Menu system that allows configuration of the desired humidity and temperature and what units for temperature you would like to use and display. The Hardware consists of an ATMEGA-16 controller, 7 Tip120 Transistors, 1 DPDT Relay, MC78T12 Regulator, LM7805 Regulator, a few passive components, a 16*2 lcd, and a few connectors.
Tag : Humidity Project, Temperature controller, AVR project

AVR Wireless Streaming Radio

2010-07-06T11:54:00.000-07:00

The project allow you streaming your radio broadcast wirelessly over internet. The wifi radio built using an Asus WL-520gu wireless router, an old USB audio headset, AVR ATmega8 and other part. If you are interested to build Wireless Streaming Radio, here is the requirement you need to prepare : Wireless connectivity through existing Wifi network; Audio output (preferably 44kHz, 16 bit stereo); Shoutcast/MP3 streaming audio decode; A display to indicate the station and currently playing song; An integrated amplifier and speaker(s); Several built in station presets; and Simple user interface, using standard radio controls (volume, tune, etc).
Gary Dion said that the radio can be controlled over Ethernet and also IR transmitter. The firmware in the project is written in C. You can download the source code here and router shell script. The project inspiration come from Jeff Keyzer.

Optical String Tuning Tool, AVR AtMega8

2010-07-06T11:39:00.000-07:00

Stimmmopped is AVR ATmega8-based project that will assists you in tuning your string instrument to a given tone. It utilizes the stroboscopic effect to give feedback about the adjustment of your instrument. When the frequency that you chose has tone then the two LEDs on the board blink. Two lines are projected at a fixed position on the string when the string vibrates with the correct frequency. If frequencies don't match, the lines appear to be blinking or moving to the observer's eye. The moving or blinking effect decreases with decreasing difference between the two frequencies.
"The project has two switches to choose the tone and instrument. Switch S1 toggles the current mode of the menu, which is either "choose instrument" or "choose tone". The 7-segment display displays the current selection. In the instrument selection mode, the display is lit up a bit brighter. Switch number two (S2) selects the tone or instrument in the given mode." said Madex (Martin), the designer.
DOWNLOAD : Source Code And Layout

Automatic Temperature Control

2010-06-29T09:33:00.000-07:00

LM35 and TL431 Automatic Temperature Control

This is an electronic circuit that can be used as automatic temperature control aapplication. The circuit switches a miniature relay ON or OFF according to the temperature detected by the one-chip temperature sensor LM35. When the LM35 detects a temperature higher than the preset level (set by VR1), the relay is actuated. When the temperature falls below the preset temperature, relay is de-energized. The circuit can be powered by any AC or DC 12V supply or battery (100mA min.)

DOWNLOAD : schematic, layout and PCB (pdf)

Battery Charger

2010-06-29T09:27:00.000-07:00

Battery Charger for Hand Held Radio

This is a handy little charger that can provide a charging current of up to 120 mA continuously for batteries in the range up to 12 volts. This project inspired by 12 volt 500 mA plug pack at an amateur auction. Two potentially useful projects resulted from this plug pack. The other is a variable power supply. The supply is housed in a small plastic enclosure 90 x 55 x 32 mm.

DOWNLOAD : Circuit

power supply

2010-06-29T09:22:00.000-07:00

Compact Variable Power Supply

This is a handy little power supply that can provide a voltage range of 1.25 to 13 volts and current up to 500 mA. The supply, created by Don Wilschefski, is housed in a small plastic enclosure 90 x 55 x 32 mm.

DOWNLOAD : Image Circuit

Small USB Device Charger

2010-06-29T09:17:00.000-07:00

Small USB Device Charger

This advance tiny USB battery powered charger is handy tools for your need. You can use it to charge almost all devices which are charged via USB, like iPods or mobile phones, with only two AA-Cells. The Most important compenent of the cicuit LT1301. This is a small step up converter for to build switching mode power supplys with only a few external components.
Electronic Project

Small Telephone Exchange Project

2010-06-27T17:04:00.000-07:00

Small Telephone Exchange

Author: Dany

Compiler: mikroPascal PRO for PIC

Description:
Small private telephone exchange, initially meant to make 2 modems (one connected to a "client", the other to a "server") communicate with each other to test a server/client system before e.g. putting the server on the web. Warning: This device is not intended to connect to the public telephone network!
www.mikroe.com

DOWNLOAD PROJECT : Small Telephone Exchange

command line editor Project

2010-06-27T17:02:00.000-07:00

PIC command line editor

Author: Dany

Compiler: mikroPascal PRO for PIC

Description:
Capable of, like a modem, receiving, editing and executing one (command) line of input. The code in this example project shows a command line editor that can be used in servers (big word) you build, based on PICs.
www.mikroe.com

DOWNLOAD PROJECT : command line editor

Telnet to RS232 Project

2010-06-27T16:57:00.000-07:00

Telnet to RS232 interface

Author: Dany

Compiler: mikroPascal PRO for PIC

Description:
This device (hard and software) can be used to control up to 6 RS232 devices via Telnet (Ethernet). Uses the Ethernet ENC library v3_5 from Yo2Lio.
www.mikroe.com

DOWNLOAD PROJECT : Telnet to RS232

TFTP Server Fat16

2010-06-27T16:40:00.000-07:00

TFTP Server (Fat16, short filenames)

Author: Dany

Compiler: mikroPascal PRO for PIC

Description:
This is a small TFTP file server for Fat16 (short file names, no subdirs), using an mmc/sd card for file storage. "Small" means the software does not have an error/retry/timeout mechanism. Uses the Ethernet ENC library v3_5 from Yo2Lio.
www.mikroe.com

DOWNLOAD PROJECT : TFTP Server

TFtp Server, Fat16, Long filenames

2010-06-24T09:11:00.000-07:00

TFtp Server, Fat16, Long filenames

Author: Dany

Compiler: mikroPascal PRO for PIC

Description:
Same as the "TFTP Server" for Fat16 but for long file names. Still no subdirs! Uses the Ethernet ENC library v3_5 from Yo2Lio.
www.mikroe.com
DOWNLOAD PROJECT : TFtp Server, Fat16, Long filenames

TFTP Server Fat32

2010-06-24T09:01:00.000-07:00

TFTP Server Fat32

Author: Dany

Compiler: mikroPascal PRO for PIC

Description:
Same as "TFTP Server", but for Fat 32 cards. Supports sub directories and long file names. More details can be found in "Tftp_Server_Fat32.htm" in the zip file. Uses the Ethernet ENC library v3_5 from Yo2Lio.
www.mikroe.com

DOWNLOAD PROJECT : TFTP Server Fat32

Serial Communication

2010-06-21T20:08:00.000-07:00

Serial Communication

Author: Natan Jimenez

Compiler: mikroBasic PRO for PIC

Description:
This project is a simple task PIC_MASTER increases the value shown by the PORTB this value at a time is sent by the serial port and displays and the PORTB the pIC_SLAVE. I hope you learn and understand programming logic.
www.mikroe.com

DOWNLOAD PROJECT : Serial Communication

SMS type keypad and usart data receiver

2010-06-19T20:09:00.000-07:00

SMS type keypad and usart data receiver

Author: Yanderson

Compiler: mikroBasic PRO for PIC

Description:
Write a message in a LCD display using 4x3 keypad, writing the message just like in a cellphone keypad, an send it via USART, to be printed in a second LCD display. Connection diagram with LCD and keypad available in the zip file. PIC16F877A.
www.mikroe.com

DOWNLOAD : PROJECT SMS type and usart

Adc Display

2010-06-19T20:04:00.000-07:00

Adc Display

Author: Natan

Compiler: mikroBasic PRO for PIC

Description:
Simple project where you may observe library behavior ADC decimal form and displayed in 3 display 7-segment.
www.mikroe.com

DOWNLOAD : PROJECT Adc Display

I2C LCD

2010-06-17T05:57:00.000-07:00

I2C LCD (real)
Author: Norbert Seibert

Compiler: mikroC PRO for PIC

Description:
This project uses a real I2C 2x16 LCD module. The advantage of this module is that it uses only two I/O pins form the MCU. Also, it is possible to have a total of three LCD's (2 x I2C and 1 parallel LCD) in one system.
www.mikroe.com

DOWNLOAD : PROJECT I2C LCD

uM-FPU

2010-06-17T05:54:00.000-07:00

uM-FPU V3.1 Examples
Author: Peter Erasmus

Compiler: mikroBasic PRO for dsPIC

Description:
The uM-FPU V3.1 chip is a 32-bit floating point coprocessor that can be easily interfaced with PIC microcontrollers, and programmed with the mikroBasic compiler, to provide support for 32-bit IEEE 754 floating point operations and 32-bit long integer operations.
www.mikroe.com

DOWNLOAD : PROJECT uM-FPU

Autopilot Control following GPS waypoints

2010-06-15T17:58:00.000-07:00

Arduino Autopilot Control

ArduPilot is a full-featured autopilot based on the Arduino open-source hardware platform. It is a custom PCB with an embedded processor (ATMega168) combined with circuitry to switch between RC control and autopilot control (that's the multiplexer/failsafe, otherwise known as a "MUX"). This controls navigation (following GPS waypoints) and altitude by controlling the rudder and throttle. These components are all open source. This autopilot is fully programmable and can have any number of GPS waypoints (including altitude) and It uses infrared (thermopile) sensors for stabilization and GPS for navigation.

PIC Debugging Tool

2010-06-14T08:55:00.000-07:00

PIC Debugging Tool

In-Circuit-Debugger is handy and easy PIC debugging tool for PIC programmers that interface to the target PIC placed- board. The device comes with MPLAB plug-ins that provides a full rich set of commands and functions in order to debug your code in real time. The project created by Electrical Engineer Atanasios Melimopoulos.
After hours of using some brands of ICDs, ICD2, etc. on different projects, I faced some hardware situations where the two pin interface ICD <-> PIC becomes annoying and sometimes difficult to work around. Apart from the fact that your target PIC must run at selected clock frequencies that allows the ICD-Uart baudrate multiplier to fit. Also, some pics do not allow the same on-hook commands upon which ICDs are based. There is no electrical isolation between the pic-target board and the USB–Serial PIC-GND interface.
tag : PIC debugger, PIC programmer tools, PIC project src
Download : In-Circuit-debugger

Digital Clock using Classic LED 7 Segment Displays

2010-06-14T08:48:00.000-07:00

Digital Clock using Classic LED 7 Segment Displays

This is a simple digital clock project using PIC16F887 and classic LED 7-Segment from HP 5082-7414 created by punky. The displays are bright red and sun light viewable. Each clock consumes about 0.25W (50mA, 5V) when the PIC16F887 operates at 250kHz (display refresh rate is about 61Hz).
Tag: digital clock, 7 segment display, PIC project src

Zener Diode Tester

2010-06-08T01:18:00.000-07:00

Zener Diode Tester

Here is a handy zener diode tester which tests zener diodes with breakdown voltages extending up to 120 volts. The main advantage of this circuit is that it works with a voltage as low as 6V DC and consumes less than 8 mA current. The circuit can be fitted in a 9V battery box. Two-third of the box may be used for four 1.5V batteries and the remaining one-third is sufficient for accommodating this circuit. In this circuit a commonly available transformer with 230V AC primary to 9-0-9V, 500mA secondary is used in reverse to achieve higher AC voltage across 230V AC terminals. Transistor T1 (BC547) is configured as an oscillator and driver to obtain required AC voltage across transformers 230V AC terminals. This AC voltage is converted to DC by diode D1 and filter capacitor C2 and is used to test the zener diodes. R3 is used as a seri- es current limiting resistor. After assembling the circuit, check DC voltage across points A and B without connecting any zener diode. Now switch on S1. The DC voltage across A-B should vary from 10V to 120V by adjusting potmeter VR1 (10k). If every thing is all right, the circuit is ready for use. For testing a zener diode of unknown value, connect it across points A and B with cathode towards A. Adjust potmeter VR1 so as to obtain the maximum DC voltage across A and B. Note down this zener value corresponding to DC voltage reading on the digital multimeter. When testing zener diode of value less than 3.3V, the meter shows less voltage instead of the actual zener value. However, correct reading is obtained for zener diodes of value above 5.8V with a tolerance of 10per cent. In case zener diode shorts, the multimeter shows 0 volts
Download : Circuit Diagram

Contactless Mains Voltage Indicator

2010-06-08T01:11:00.000-07:00

Contactless Mains Voltage Indicator

This is a CMOS IC (CD4033) based circuit which can be used to detect presence of mains AC voltage without any electrical contact with the conductor carrying AC current/voltage. Thus it can be used to detect mains AC voltage without removing the insulation from the conductor. Just take it in the vicinity of the conductor and it would detect presence of AC voltage. If AC voltage is not present, the display would randomly show any digit (0 through 9) permanently. If mains supply is available in the conductor, the electric field would be induced into the sensing probe. Since IC used is CMOS type, its input impedance is extremely high and thus the induced voltage is sufficient to clock the counter IC. Thus display count advances rapidly from 0 to 9 and then repeats itself. This is the indication for presence of mains supply. Display stops advancing when the unit is taken away from the mains carrying conductor. For compactness, a 9-volt PP3 battery may be used for supply to the gadget
Download : Circuit Diagram

A simple Remote control Tester

2010-06-08T01:00:00.000-07:00

A simple Remote control Tester

Here is a handy gadget for testing of infrared (IR) based remote control transmitters used for TVs and VCRs etc. The IR signals from a remote control transmitter are sensed by the IR sensor module in the tester and its output at pin 2 goes low. This in turn switches on transistor T1 and causes LED1 to blink. At the same time, the buzzer beeps at the same rate as the incoming signals from the remote control transmitter. The pressing of different buttons on the remote control will result in different pulse rates which would change the rate at which the LED blinks or the buzzer beeps. When no signal is sensed by the sensor module, output pin 2 of the sensor goes high and, as a result, transistor T1 switches off and hence LED1 and buzzer BZ1 go off. This circuit requires 5V regulated power supply which can be obtained from 9V eliminator and connected to the circuit through a jack. Capacitor C1 smoothes DC input while capacitor C2 suppresses any sudden spikes appearing in the input supply. Here, a plastic moulded sensor has been used so that it can easily stick out from a cut in the metal box in which it is housed. It requires less space. Proper grounding of the metal case will ensure that the electromagnetic emissions which are produced by tube-lights and electronic ballasts etc (which lie within the bandwidth of receiver circuit) are effectively grounded and do not interfere with the functioning of the circuit. The proposed layout of the box containing the circuit is shown in the figure. The 9-volt DC supply from the eliminator can be fed into the jack using a banana-type plug.
Tech. Editors note: In fact, the complete gadget can be assembled in the eliminators housing itself and a cut can be made in its body for exposing the IR modules sensor part.
Download : Circuit Diagram

High Resistance Voltmeter

2010-06-08T00:51:00.000-07:00

High Resistance Voltmeter

The full-scale deflection of the universal high-input-resistance voltmeter circuit shown in the figure depends on the function switch position as follows:
(a) 5V dc on position 1
(b) 5V ac rms in position 2
(c) 5V peak ac in position 3
(d) 5V ac peak-to-peak in position 4
The circuit is basically a voltage-to-current converter. The design procedure is as follows:
Calculate RI according to the application from one of the following equations:
(a) dc voltmeter: RIA = full-scale EDC/IFS
(b) rms ac voltmeter (sine wave only): RIB = 0.9 full-scale ERMS/ IFS
(c) Peak reading voltmeter (sine wave only): RIC = 0.636 full-scale EPK/IFS
(d) Peak-to-peak ac voltmeter (sine wave only): RID = 0.318 full-scale EPK-TO-PK / IFS
The term IFS in the above equations refers to meters full-scale deflection current rating in amperes.
It must be noted that neither meter resistance nor diode voltage drops affects meter current.
A high-input-resistance op-amp, a bridge rectifier, a microammeter, and a few other discrete components are all that are required to realise this versatile circuit. This circuit can be used for measurement of dc, ac rms, ac peak, or ac peak-to-peak voltage by simply changing the value of the resistor connected between the inverting input terminal of the op-amp and ground. The voltage to be measured is connected to non-inverting input of the op-amp.
Download : Circuit Diagram

The Link Telephone Intercom

2010-06-08T00:27:00.000-07:00

The Link Telephone Intercom

The Link circuitry is simple and efficient, employing just two ICs, half a dozen transistors, and a handful of garden variety components. It all runs on 12 volts and is easily assembled. You can have your own home intercom between the kitchen, the garage, the rumpus room and at your poolside barby and all for less than $100!
The Link intercom has been designed in such a way that you can buy parts for it off the shelf at just about any decent electronics retail chain. It uses old pulse dial handsets and replaces the AC bell set with a 9 volt DC buzzer. The whole circuit runs from a 12 volt regulated DC supply and is suitable for short term battery operation (eg: Gel Cell). It is suitable for radio field days and sporting events (providing you can scrounge enough 4 wire cable) and may find a place in pre-schools, old folks homes, boy scout/girl guide halls, churches, kids tree houses/fortresses, or maybe even more serious uses such as small offices, factories, workshops and many other applications.
The Link is designed to enable one call at a time within a small area (about 100 meters from the black box is about the max per handset) and is not suitable for connection to the PSTN (public network) as the voltages and currents used by the PSTN are higher, and will damage the simpler 12 volt circuitry, that employs CMOS ICs etc. The Link will run quite happily off a 12 volt regulated DC supply of only 200mA or so, and this can be a simple affair, such as a DC plug pack, wired to a 7812 regulator chip and appropriate filter caps on the output. Add some leds if you want!
Overview
The Link telephone intercom is designed around two ICs. The first, IC1, is an NE 556 dual timer chip, which is wired up to provide dial tone, ring tone (busy tone too, which will be explained along with a few add-ons to be mentioned later on) and ring pulses for the ringer circuit attached to each line circuit. The other chip, IC 2, is a CD 4017B decade counter, which is wired to count each train of dial pulses as they are received and buffered by the two opto-couplers, OC1 and OC 2 and their associated R/C networks.
Line Circuits
Each phone handset is connected by a four wire circuit from the black box. Two wires (normally tagged white and blue here in Oz) are for speech and dialing functions, whereas the other two (tagged locally as red and black) are for the ring pulses supplied by the ringer circuit to each DC buzzer inside the handsets. When a phone (eg: #1 for our discussion) is picked up in its off hook condition, a DC loop is formed by the following components: DC circuitry inside the phone, the 1K winding of transformer TX, and back to 0V- earth. Taken from the +12 volts terminal, through the Leds inside OC1 and OC2 and back to the phone handset.
Making A Call
Dial tone is provided to the calling partys phone when the Link is in its reset condition (no calls in progress) via capacitor C3 and the 8 ohm winding (8R) of TX to 0v- earth. This and the other service tones are generated by IC1a, while ring pulses are generated by IC1b. When a calling partys phone is off hook, the leds force the photo transistors to switch on hard, pulling pins 13 and 14 of IC2 to 0 volts ground. When the dial inside the phone handset is pulled back and released, the collector lead of OC2s transistor is held low at 0 volts by the slow release charging of C5. Pin 13 of IC2 is a CE (chip enable) input, and needs to stay at a logic low (near 0 volts) to enable pin 14 to count the dial pulses. So while impulsing occurs, pin 13 stays low, and pin 14 alternates between logic high and low as the led emulates each dial pulse train, until the last pulse in the train is received.
Dialing Into The Register
When caller number #1 dials phone number # 4, those four pulses appear across the leds inside OC1 and OC2. The decade counter, acting as a Register (a storage device used in communications equipment for storing dialed digits) counts these pulses, turning its output pins on and off inn unison, with the last dial pulse causing the counter to rest on the last output pin that is turned on. The complete sequence for a maximum of ten pulses in the one pulse train, is (pin 3 is always at logic high at reset) 2,4,7,10, and then 1,5,6,9,11 and then finally pin 3. So when the number 4 is dialed, the counter would step through pins 2,4,7, and then land on pin 10, which is connected to phone #4s ringer circuit via Q4s base lead.
The Ringer Circuit
Each line circuit consists of the individual phone handset, the DC buzzer mounted inside it, the common connections to TX and the cathode of OC2s led, as well as transistors Q1 to Q4 and common driver transistor Q5. With pin 3 of IC2 at logic high on reset, diode D3 enables IC2a to provide a Dial Tone from pin 5. When a number is dialed, pin 3 of IC2 goes low on the first dial pulse, removing the logic high via D4 from pins 12 and 8 of IC1b, thus enabling it to charge up C3, and produce ring pulses to IC1a via diode D5, (from pin 9 to pin 4). After about 2 seconds, ring pulses commence, and the modulated dial tone (which then by default becomes an interrupted Ring Tone to the caller) is produced at pin 5 of IC1a, indicating the progress of the call.
True Ring Trip
When the called party answers the call, transistor QX with trimpot R6, (adjusted to detect both phones being off-hook,) triggers the led and phototransistor inside OC3. This halts the ring pulses and ring tone supplied by IC1a and IC1b for the duration of that call, by supplying a logic high potential to pins 12 and 8 of IC1b via D6. When the call is over, and both parties have hung up their phone handsets (eg: back to the on-hook status,) the DC loop formed by the handsets, TX and OC1/OC2 is broken. Pin 13 of IC2 returns to its reset potential of logic high, and extends this high to pin 15 (Reset) of the 4017 decade counter chip, which disables the output selected during the dialing operation, and enables pin 3 to high, thus restoring Dial Tone to the next caller via pin 4 of IC1a.
Resetting The Link
Thus the Link is fully reset and ready for another call. As you can see, it may seem a little complicated to follow the progression through a call, particularly if you havent been involved with phones and logic chips much before. At the end of the day, you have some simple counting, pulsing and interfacing circuitry, which will perform all the necessary tasks of a basic intercom, and all at a reasonable cost. I used some formatted matrix board for the p.c.b and IC sockets for all ICs and OC/OC2. I also found that a heat sink fin for the 7812 regulator chip was unnecessary. A box could be used for housing the Link circuitry, and some kind of screw terminal block or ID block (like a small 10 pair KRONE junction box) could be used to terminate the wiring at the box to make it look more professional. Remember these two things. If you leave a phone off-hook you will lock up the Link and if you pick up a phone when someone else is dialing, wrong numbers will result. Apart from that, have fun!
Download : Part list

Off line Telephone tester

2010-06-07T23:51:00.000-07:00

Off line Telephone tester

Here is a circuit of an off-line telephone tester which does not require any telephone line for testing a telephone instrument. The circuit is so simple that it can be easily assembled even by a novice having very little knowledge of electronics. A telephone line may be considered to be a source of some 50 volts DC with a source impedance of about 1 kilo-ohm. During ringing, in place of DC, an AC voltage of 70 to 80 volts (at 17 to 25 Hz) is present across the telephone line. When the subscriber lifts the handset, the same is sensed by the telephone exchange and the ringing AC voltage is disconnected and DC is reconnected to the line. Lifting of the handset from the telephone cradle results in shunting of the lines two wires by low impedance of the telephone instrument. As a result, 50V DC level drops to about 12 volts across the telephone instrument. During conversation, the audio gets superimposed on this DC voltage. Since any DC supply can be used for testing a telephone instrument, the same is derived here from AC mains using step-down transformer X1. Middle point of the transformers secondary has been used as common for the two full-wave rectifiers one comprising diodes D1 and D2 together with smoothing capacitor C1 and the other formed by diodes D3 and D4 along with filter capacitor C2. The former supplies about 12 volts for the telephone instrument through primary of transformer X2 which thus simulates a source impedance, and a choke which blocks AC audio signals present in the secondary of transformer X2. The AF signal available in secondary of X2 is sufficiently strong to directly drive a 32-ohm headset which is connected to the circuit through headphone socket SK1 via rotary switch S2. During ringing, a pulsating DC voltage from transformer X1 via rectifier diode D5, push-to-on switch S3, and contact B of rotary switch S2 is applied across secondary of transformer X2. The boosted voltage available across primary of transformer X2 is sufficient to drive the ringer in the telephone instrument. Please avoid pressing of switch S3 for more than a few seconds at a time to prevent damage to the circuit due to high voltage across primary of transformer X2. The circuit also incorporates a music IC (UM66) whose output is connected to secondary of transformer X2 via switch S2 after suitably boosting its output with the help of darlington transistor pair T1 and T2. This output can be used to test the audio section of any telephone instrument. After having assembled the circuit satisfactorily, the following procedure may be followed for testing a telephone instrument:
1. Connect the telephone to the terminals marked To Telephone Under Test and switch on mains (switch S1).
2. To test the ringer portion, flip switch S2 to position B and press S3 for a moment. You should hear the ring in case the ringer circuit of the telephone under test is working. Please ensure that handset is on cradle during this test.
3. For testing the audio section, flip switch S1 to position C and connect a headphone to socket SK1. Pick the telephone handset and speak into its microphone. If audio section is working satisfactorily, you should be able to hear your speach via the headphone. If you dial a number, you should be able to hear the pulse clicks or pulse tone in the headphone, depending on whether the telephone under test is functioning in pulse or tone mode. If the telephone under test has a built-in musical hold facility, on pressing the hold button you should be able to hear the music. Now flip switch S2 to position A. You should be able to hear music generated by IC1 through earpiece of the handset of the telephone under test, indicating propor functioning of the AF amplifier section. The circuit can be assembled on a small piece of veroboard. Try to mount the two transformers on opposite sides of the board, displaced by 90 degrees. Always keep handy multi-type modular plugs for testing various types of telephones. Mount all switches, sockets and LEDs on the front of testing panel.

Audio Visual Ringer

2010-05-16T22:50:00.000-07:00

Audio Visual Ringer

Many a times one needs an extra telephone ringer in an adjoining room to know if there is an incoming call. For example, if the telephone is installed in the drawing room you may need an extra ringer in the bedroom. All that needs to be done is to connect the given circuit in parallel with the existing telephone lines using twin flexible wires. This circuit does not require any external power source for its operation. The section comprising resistor R1 and diodes D5 and LED1 provides a visual indication of the ring. Remaining part of the circuit is the audio ringer based on IC1 (BA8204 or ML8204). This integrated circuit, specially designed for telecom application as bell sound generator, requires very few external parts. It is readily available in 8-pin mini DIP pack.
Resistor R3 is used for bell sensitivity adjustment. The bell frequency is controlled by resistor R5 and capacitor C4, and the repeat frequency is controlled by resistor R4 and capacitor C3. A little experimentation with the various values of the resistors and capacitors may be carried out to obtain desired pleasing tone. Working of the circuit is quite simple. The bell signal, approximately 75V AC, passes through capacitor C1 and resistor R2 and appears across the diode bridge comprising diodes D1 to D4. The rectified DC output is smoothed by capacitor C2. The dual-tone ring signal is output from pin 8 of IC1 and its volume is adjusted by volume control VR1. Thereafter, it is impressed on the piezoceramic sound generator

Telephone Line Vigilant

2010-05-16T07:27:00.000-07:00

Telephone Line Vigilant

Here is a telephone line vigilant circuit to guard against mis- use of your telephone lines. It monitors telephone lines round the clock and provides visual as well as an audio warning (when someone is using your telephone lines) which can be heard anywhere in the house. Another advantage of using this circuit is that one comes to know of the misuse and snapping of the lines (due to any reason) instantaneously on its occurance. This enables the subscriber to take necessary remedial measures in proper time.
subscriber himself is using his telephone (handset off-cradle) while the vigilant circuit is on, the buzzer beeps once every 5 seconds since the vigilant circuit cannot distinguish between self-use of the subscriber lines or by any unauthorised person. Thus to avoid unnecessary disturbance, it is advisable to install the vigilant unit away from the phone. However, if one wishes to fit the unit near the telephone then switch S1 may be flipped to off position to switch off the buzzer. But remember to flip the switch to on position while replacing the handset on cradle.
Irrespective of telephone line polarity at the input to the circuit, proper DC polarity is maintained across C1 due to bridge rectifier comprising diodes D1 to D4. The DC voltage developed across capacitor C1 is used to check telephone line condition. This circuit draws negligible current from telephone line; thus when it is connected to the telephone line, the normal telephone operation is not affected. The circuit may be divided into two parts. The first part comprises zener D9, transistors T1 to T4 and diode D5. It is used to verify whether telephone line loop is intact or discontinuous. The second part comprising zener D10 and transistors T5 to T10 is used to check whether telephone line is in use (or misuse) or not. The zener diode D9 (3.3V) conducts when phone line loop is intact and not broken. Zener D9 sets control voltage for transistors T1, T2 and T3 to conduct and for T4 to cut off. As a result, green LED lights but no sound is heard from the buzzer.

When phone line loop is discontinuous, no voltage is available across capacitor C1. Thus zener D9 and transistors T1, T2 and T3 do not conduct while T4 conducts. Now green LED extinguishes and a continuous sound is heard from the buzzer. When telephone line is alright but is not in use, zener D10 conducts as voltage across capacitor C1 is quite high. This results in conduction of transistors T5 and T6 and cutting off of transistor T7 (as collector of transistor T6 is near ground potential). Thus positive 9V rail is not extended to the following multivibrator circuit built around transistors T8 and T9. Consequently, the red LED is not lit and buzzer does not sound. When phone line is in use, zener D10 does not conduct. As a result, transistors T5 and T6 also do not conduct, while transistor T7 conducts. Now +9V is extended to multivibrator circuit. This multivibrator is designed such that collector of transistor T9 goes high once every 5 seconds to forward bias transistor T10 and it conducts. Thus at every 5-second interval a beep sound is heard from buzzer. The beep sound interval can be increased or decreased by changing the value of capacitor C3 while the volume can be adjusted with the help of preset VR3

Telephone Headgear

2010-05-14T01:02:00.000-07:00

Telephone Headgear

A compact, inexpensive and low component count telcom head- set can be constructed using two readily available transistors and a few other electronic components. This circuit is very useful for hands-free operation of EPABX and pager communication. Since the circuit draws very little current, it is ideal for parallel operation with electronic telephone set. Working of the circuit is simple and straightforward. Resistor R1 and an ordinary neon glow- lamp forms a complete visual ringer circuit. This simple arrangement does not require a DC blocking capacitor because, under idle conditions, the telephone line voltage is insufficient to ionise the neon gas and thus the lamp does not light. Only when the ring signal is being received, it flashes at the ringing rate to indicate an incoming call. The bridge rectifier using diodes D1 through D4 acts as a polarity guard which protects the electronic circuit from any changes in the telephone line polarity. Zener diode D5 at the output of this bridge rectifier is used for additional circuit protection. Section comprising transistor T1, resistors R2, R3 and zener diode D6 forms a constant voltage regulator that provides a low voltage output of about 5 volts. Dial tone and speech signals from exchange are coupled to the receiving sound amplifier stage built around transistors T2 and related parts, i.e. resistors R7, R6 and capacitor C5. Amplified signals from collector of transistor T2 are connected to dynamic receiver RT-200 (used as earpiece) via capacitor C7. A condenser microphone, connected as shown in the circuit, is used as transmitter. Audio signals developed across the microphone are coupled to the base of transistor T1 via capacitor C3. Resistor R4 determines the DC bias required for the microphone. After amplification by transistor T1, the audio signals are coupled to the telephone lines via the diode bridge. The whole circuit can be wired on a very small PCB and housed in a medium size headphone, as shown in the illustration. For better results at low line currents, value of resistor R2 may be reduced after testing

Smart Phone light

2010-05-14T00:37:00.000-07:00

Smart Phone light

The circuit shown here is used to switch on a lamp when the telephone rings, if the ambient light is insufficient. The circuit uses only two ICs and it can be implemented very easily. A light dependent resistance (LDR), with about 5 kilo-ohms resistance in the ambient light and greather than 100 kilo-ohms in darkness, is at the heart of the circuit. The circuit is fully isolated from the phone lines and it draws current only when the phone rings. The circuit provides automatic switching on of a lamp during darkness when the phone is kept in a place such as the bedroom. The lamp can be battery powered to provide light during power failure or load shedding. This avoids delay in attending to a call. The light switches off automatically after a programmable time period and it needs no attention at all. If required, the lamp lighting period can be extended by simply pressing a pushbutton switch (S1). The first part of the circuit functions as a ring detector. When telephone is on-hook, around 48V DC is present across the TIP and RING terminals. The diode in the opto-coupler is off during this condition and it draws practically no current from he telephone lines. The opto-coupler also isolates the circuit from the telephone lines. Transistor in the opto-coupler is normally off and a voltage of +5V is present at the ring indicator line. When telephone rings, an AC voltage of around 70-80V AC, which is present across the telephone lines, is used to turn on the diode inside the opto-coupler (IC2) which in turn switches on transistor inside the opto-coupler. The voltage at its collector passes through 0-volt level during ringing to trigger IC3 74LS123(A) monostable flip-flop. The other opto-coupler (IC1) is used to detect the ambient light condition. When there is sufficient light, LDR has a low resistance of about 5 kilo-ohms and the transistor inside the opto-coupler is in on state. When there is insufficient light available, the resistance of LDR increases to a few mega-ohms and the transistor switches to off state. Thus the DC voltage present at the collector of transistor inside the opto-coupler is normally 0V and it jumps to 5V when there is no light or insufficient light. The 74LS123 retriggerable monostable multivibrator is used to generate a programmable pulse-width. The first monostable 74LS123(A) generates a pulse from the trigger input available during ringing, provided its pin 2 input (marked B) is logic high (i.e. during darkness). It remains high for the programmed duration and switches back to 0V at the end of the pulse period. This high-to-low transition (trailing edge) is used to trigger the second monostable flip-flop 74LS123(B) in the same package. Output of the second monostable is used to control a relay. The lamp being controlled via the N/O contacts of the relay gets switched on. The on period can be extended by simply pressing pushbutton switch S1. If nobody attends the phone, the light turns off automatically after the specific time period equal to the pulse-width of the second flip-flop. The light sensitivity of LDR can be changed by changing resistance R2 connected at collector of the transistor in light monitor circuit. Similarly, switch-on period of the lamp can be controlled by changing capacitor C3s value in the second 74123(B) monostable circuit

Telephone Number Display

2010-04-20T00:50:00.000-07:00

Telephone Number Display

The given circuit, when connected in parallel to a telephone, displays the number dialled from the telephone set using the DTMF mode. This circuit can also show the number dialled from the phone of the called party. This is particularly helpful for receiving any number over the phone lines. The DTMF signal generated by the phone on dialling a numberis decoded by DTMF decoder CM8870P1 (IC1), which converts the received DTMF signal into its equivalent BCD number that corresponds to the dialled number. This binary number is stored sequentially in 10 latches each time a number is dialled from the phone. The first number is stored in IC5A (1/2 of CD4508) while the second number is stored in IC5B and so on. The binary output from IC1 for digit 0 as decoded by IC1 is 10102 (=1010), and this cannot be displayed by the seven-segment decoder, IC10. Therefore the binary output of IC1 is passed through a logic-circuit which converts an input of 10102 into 00002 without affecting the inputs 1 through 9. This is accomplished by gates N13 through N15 (IC11) and N1 (IC12). The storing of numbers in respective latches is done by IC2 (4017). The data valid output from pin 15 of IC1 is used to clock IC2. The ten outputs of IC2 are sequentially connected to the store and clear inputs of all the latches, except the last one, where the clear input is tied to ground. When an output pin of IC2 is high, the corresponding latch is cleared of previous data and kept ready for storing new data. Then, on clocking IC2, the same pin becomes low and the data present at the inputs of that latch at that instant gets stored and the next latch is cleared and kept ready. The similar input and output pins of all latches are connected together to form two separate input and output buses. There is only one 7-segment decoder/driver IC10 for all the ten displays. This not only reduces size and cost but reduces power requirement too. The output from a latch is available only when its disable pins (3 and 15) are brought low. This is done by IC3, IC12 and IC13. IC3 is clocked by an astable multivibrator IC4 (555). IC3 also drives the displays by switching corresponding transistors. When a latch is enabled, its corresponding display is turned on and the content of that latch, after decoding by IC10, gets displayed in the corresponding display. For instance, contents of IC5A are displayed on display DIS1, that of IC5B on DIS2 and so on. The system should be connected to the telephone lines via a DPDT switch (not shown) for manual switching, otherwise any circuit capable of sensing handset�s off-hook condition and thereby switching relays, etc. can be used for automatic switching. The power-supply switch can also be replaced then. Though this circuit is capable of showing a maximum of ten digits, one can reduce the display digits as required. For doing this, connect the reset pin of IC2, say, for a 7-digit display, with S6 output at pin 5. The present circuit can be built on a veroboard and housed in a suitable box. The displays are common-cathode type. To make the system compact, small, 7-segment displays can be used but with some extra cost. Also, different colour displays can be used for the first three or four digits to separate the exchange code/STD code, etc. The circuit can be suitably adopted for calling-line display.

Cordless phone backup

2010-04-20T00:43:00.000-07:00

Cordless phone backup

Normally the base of a cordless phone has an adaptor and the handset has Ni-Cd cells for its operation. The base unit becomes inoperative in case of power failure. In such conditions, it is better to provide a backup using Ni-Cd cells externally. Here is a simple circuit which can be used with cordless phone SANYO CLT-420 or similar sets.
The working is simple. When AC mains is present, Ni-Cd cells are charged through IC LM317L, which is wired as a current source. Also, diode D3 is reverse-biased, which keeps Ni-Cd cells isolated from positive rail. When AC mains goes off, the Ni-Cd cells provide supply to the cordless phone base unit through diode D3. A green LED is used to indicate the presence of AC mains.
Each Ni-Cd cell costs around Rs 34, and the cost of the backup unit, including the box and cells, would not exceed Rs 300. Hence the circuit is well worth the investment

Remote control using Telephone

2010-04-20T00:25:00.000-07:00

Remote control using Telephone

Here is a teleremote circuit which enables switching on and off of appliances through telephone lines. It can be used to switch appliances from any distance, overcoming the limited range of infrared and radio remote controls.
The circuit described here can be used to switch up to nine appliances (corresponding to the digits 1 through 9 of the telephone key-pad). The DTMF signals on telephone instrument are used as control signals. The digit 0 in DTMF mode is used to toggle between the appliance mode and normal telephone operation mode. Thus the telephone can be used to switch on or switch off the appliances also while being used for normal conversation.
The circuit uses IC KT3170 (DTMF-to-BCD converter), 74154 (4-to-16-line d-multiplexer), and five CD4013 (D flip-flop) ICs. The working of the circuit is as follows.
Once a call is established (after hearing ring-back tone), dial 0 in DTMF mode. IC1 decodes this as 1010, which is further demultiplexed by IC2 as output O10 (at pin 11) of IC2 (74154). The active low output of IC2, after inversion by an inverter gate of IC3 (CD4049), becomes logic 1. This is used to toggle flip-flop-1 (F/F-1) and relay RL1 is energised. Relay RL1 has two changeover contacts, RL1(a) and RL1(b). The energised RL1(a) contacts provide a 220-ohm loop across the telephone line while RL1(b) contacts inject a 10kHz tone on the line, which indicates to the caller that appliance mode has been selected. The 220-ohm loop on telephone line disconnects the ringer from the telephone line in the exchange. The line is now connected for appliance mode of operation.
If digit 0 is not dialed (in DTMF) after establishing the call, the ring continues and the telephone can be used for normal conversation. After selection of the appliance mode of operation, if digit 1 is dialed, it is decoded by IC1 and its output is 0001. This BCD code is then d-multiplexed by 4-to-16-line D-multiplexer IC2 whose corresponding output, after inversion by a CD4049 inverter gate, goes to logic 1 state. This pulse toggles the corresponding flip-flop to alternate state. The flip-flop output is used to drive a relay (RL2) which can switch on or switch off the appliance connected through its contacts. By dialing other digits in a similar way, other appliances can also be switched on or off.
Once the switching operation is over, the 220-ohm loop resistance and 10kHz tone needs to be removed from the telephone line. To achieve this, digit 0 (in DTMF mode) is dialed again to toggle flip-flop-1 to de-energise relay RL1, which terminates the loop on line and the 10kHz tone is also disconnected. The telephone line is thus again set free to receive normal calls.This circuit is to be connected in parallel to the telephone instrument.

Multipurpose Circuit for Telephone

2010-04-20T00:13:00.000-07:00

Multipurpose Circuit for telephone

This add-on device for telephones can be connected in parallel to the telephone instrument.
The circuit provides audio-visual indication of on-hook, off-hook, and ringing modes. It can also be used to connect the telephone to a cid (caller identification device) through a relay and also to indicate tapping or misuse of telephone lines by sounding a buzzer.
In on-hook mode, 48V dc supply is maintained across the telephone lines. In this case, the bi-colour led glows in green, indicating the idle state of the telephone. The value of resistor r1 can be changed some what to adjust the led glow, without loading the telephone lines (by trial and error).
In on-hook mode of the hand-set, potentiometer vr1 is so adjusted that base of t1 (bc547) is forward biased, which, in turn, cuts off transistor t2 (bc108). While adjusting potmeter vr1, ensure that the led glows only in green and not in red.
When the hand-set is lifted, the voltage drops to around 12V dc. When this happens, the voltage across transistor t1s base-emitter junction falls below its conduction level to cut it off. As a result transistor pair t2-t3 starts oscillating and the piezo-buzzer starts beeping (with switch s1 in on position). At the same time, the bi-colour led glows in red.
In ringing mode, the bi-colour led flashes in green in synchronisation with the telephone ring.
A cid can be connected using a relay. The relay driver transistor can be connected via point a as shown in the circuit. To use the circuit for warning against misuse, switch s1 can be left in on position to activate the piezo-buzzer when anyone tries to tap the telephone line. (When the telephone line is tapped, its like the off-hook mode of the telephone hand-set.)
Two 1.5V pencil cells can provide Vcc1 power supply, while a separate power supply for Vcc2 is recommended to avoid draining the battery. However, a single 6-volt supply source can be used in conjunction with a 3.3V zener diode to cater to both Vcc2 and Vcc1 supplies.

Conversation Recorder to Telephone

2010-04-19T23:59:00.000-07:00

Conversation Recorder

This circuit enables automatic switching-on of the tape recorder when the handset is lifted. The tape recorder gets switched off when the handset is replaced. The signals are suitably attenuated to a level at which they can be recorded using the MIC-IN socket of the tape recorder.
Points X and Y in the circuit are connected to the telephone lines. Resistors R1 and R2 act as a voltage divider. The voltage appearing across R2 is fed to the MIC-IN socket of the tape recorder. The values of R1 and R2 may be changed depending on the input impedance of the tape recorders MIC-IN terminals. Capacitor C1 is used for blocking the flow of DC.
The second part of the circuit controls relay RL1, which is used to switch on/off the tape recorder. A voltage of 48 volts appears across the telephone lines in on-hook condition. This voltage drops to about 9 volts when the handset is lifted. Diodes D1 through D4 constitute a bridge rectifier/polarity guard. This ensures that transistor T1 gets voltage of proper polarity, irrespective of the polarity of the telephone lines.
During on-hook condition, the output from the bridge (48V DC) passes through 12V zener D5 and is applied to the base of transistor T1 via the voltage divider comprising resistors R3 and R4. This switches on transistor T1 and its collector is pulled low. This, in turn, causes transistor T2 to cut off and relay RL1 is not energised.
When the telephone handset is lifted, the voltage across points X and Y falls below 12 volts and so zener diode D5 does not conduct. As a result, base of transistor T1 is pulled to ground potential via resistor R4 and thus is cut off. Thus, base of transistor T2 gets forward biased via resistor R5, which results in the energisation of relay RL1. The tape recorder is switched on and recording begins.
The tape recorder should be kept loaded with a cassette and the record button of the tape recorder should remain pressed to enable it to record the conversation as soon as the handset is lifted. Capacitor C2 ensures that the relay is not switched on-and-off repeatedly when a number is being dialled in pulse dialing mode.

Phone Broadcaster

2010-04-17T00:35:00.000-07:00

Phone Broadcaster

Here is a simple yet very useful circuit which can be used to eavesdrop on a telephone conversation. The circuit can also be used as a wireless telephone amplifier.
One important feature of this circuit is that the circuit derives its power directly from the active telephone lines, and thus avoids use of any external battery or other power supplies. This not only saves a lot of space but also money. It consumes very low current from telephone lines without disturbing its performance. The circuit is very tiny and can be built using a single-IC type veroboard that can be easily fitted inside a telephone connection box of 3.75 cm x 5 cm.
The circuit consists of two sections, namely, automatic switching section and FM transmitter section.
Automatic switching section comprises resistors R1 to R3, preset VR1, transistors T1 and T2, zener D2, and diode D1. Resistor R1, along with preset VR1, works as a voltage divider. When voltage across the telephone lines is 48V DC, the voltage available at wiper of preset VR1 ranges from 0 to 32V (adjustable). The switching voltage of the circuit depends on zener breakdown voltage (here 24V) and switching voltage of the transistor T1 (0.7V). Thus, if we adjust preset VR1 to get over 24.7 volts, it will cause the zener to breakdown and transistor T1 to conduct. As a result collector of transistor T1 will get pulled towards negative supply, to cut off transistor T2. At this stage, if you lift the handset of the telephone, the line voltage drops to about 11V and transistor T1 is cut off. As a result, transistor T2 gets forward biased through resistor R2, to provide a DC path for transistor T3 used in the following FM transmitter section.
The low-power FM transmitter section comprises oscillator transistor T3, coil L1, and a few other components. Transistor T3 works as a common-emitter RF oscillator, with transistor T2 serving as an electronic on/off switch. The audio signal available across the telephone lines automatically modulates oscillator frequency via transistor T2 along with its series biasing resistor R3. The modulated RF signal is fed to the antenna. The telephone conversation can be heard on an FM receiver remotely when it is tuned to FM transmitter frequency.
Lab Note: During testing of the circuit it was observed that the telephone used was giving an engaged tone
when dialed by any subscriber. Addition of resistor R5 and capacitor C6 was found necessary for rectification of the fault.

Telephone call meter using calculator And COB

2010-04-17T00:16:00.000-07:00

Telephone call meter using calculator & COB

In this circuit, a simple calculator, in conjunction with a COB (chip-on-board) from an analogue quartz clock, is used to make a telephone call meter. The calculator enables conversion of STD/ISD calls to local call equivalents and always displays current local call-meter reading.
The circuit is simple and presents an elegant look, with feather-touch operation. It consumes very low current and is fully battery operated. The batteries used last more than a year.
Another advantage of using this circuit is that it is compatible with any type of pulse rate format, i.e. pulse rate in whole number, or whole number with decimal value. Recently, the telephone department announced changes in pulse rate format, which included pulse rate in whole number plus decimal value. In such a case, this circuit proves very handy.
To convert STD/ISD calls to local calls, this circuit needs accurate 1Hz clock pulses, generated by clock COB. This COB is found inside analogue quartz wall clocks or time-piece mechanisms. It consists of IC, chip capacitors, and crystal that one can retrieve from scrap quartz clock mechanisms. These can be purchased from watch-repairing shops for less than Rs 20.
Normally, the COB inside clock mechanism will be in good condition. However, before using the COB, please check its serviceability by applying 1.5V DC across terminals C and D, as shown in the figure. Then check DC voltage across terminals A and B; these terminals in a clock are connected to a coil. If the COB is in good condition, the multimeter needle would deflect forward and backward once every second. In fact, 0.5Hz clock is available at terminals A and B, with a phase difference of 90o. The advantage of using this COB is that it works on a 1.5V DC source.
The clock pulses available from terminal A and B are combined using a bridge, comprising diodes D1 to D4, to obtain 1Hz clock pulses. These clock pulses are applied to the base of transistor T1. The collector and emitter of transistor T1 are connected across calculators = terminals.
The number of pulses forming an equivalent call may be determined from the latest telephone directory. However, the pulse rate (PR) found in the directory cannot be used directly in this circuit. For compatibility with this circuit, the pulse rate applicable for a particular place/distance, based on time of the day/holidays, is converted to pulse rate equivalent (PRE) using the formula PRE = 1/PR.
You may prepare a look-up table for various pulse rates and their equivalents (see Table). Suppose you are going to make an STD call in pulse rate 4. Note down from the table the pulse rate equivalent for pulse rate 4, which is 0.25. Please note that on maturity of a call in the telephone exchange, the exchange call meter immediately advances to one call and it will be further incremented according to pulse rate. So one call should always be included before counting the calls.
For making call in pulse rate 4, slide switch S1 to off (pulse set position) and press calculator buttons in the following order: 1, +, 0.25, =. Here, 1 is initial count, and 0.25 is PRE. Now calculator displays 1.025. This call meter is now ready to count. Now make the call, and as soon as the call matures, immediately slide switch S1 to on (start/standby position). The COB starts generating clock pulses of 1 Hz. Transistor T1 conducts once every second, and thus = button in calculator is activated electronically once every second. The calculator display starts from 1.25, advancing every second as follows:
1.25, 1.5, 1.75, 2.00, 2.25, 2.50, and so on.
After finishing the call, immediately slide switch S1 to off position (pulse set position) and note down the local call meter reading from the calculator display. If decimal value is more than or equal to 0.9, add another call to the whole number value. If decimal value is less than 0.9, neglect decimal value and note down only whole numbers.

Having secrecy in parallel telephones

2010-04-17T00:08:00.000-07:00

Having secrecy in parallel telephones

Often a need arises for connection of two telephone instruments in parallel to one line. But it creates quite a few problems in their proper performance, such as overloading and overhearing of the conversation by an undesired person. In order to eliminate all such problems and get a clear reception, a simple scheme is presented here (Fig. 1).
This system will enable the incoming ring to be heard at both the ends. The DPDT switch, installed with each of the parallel telephones, connects you to the line in one position of the switch and disconnects you in the other position of the switch. At any one time, only one telephone is connected to the line. To receive a call at an end where the instrument is not connected to the line, you just have to flip the toggle switch at your end to receive the call, and act as usual to have a conversation. As soon as the position of the toggle switch is changed, the line gets transferred to the other telephone instrument.
Mount one DPDT toggle switch, one telephone ringer, and one telephone terminal box on two wooden electrical switchboards, as shown in Fig. 3. Interconnect the boards using a 4-pair telephone cable as per Fig. 1. The system is ready to use. Ensure that the two lower leads of switch S2 are connected to switch S1 after reversal, as shown in the figure.

Telephone line based audio muting and light on circuit

2010-04-16T23:53:00.000-07:00

Telephone line based audio muting and light on circuit

Very often when enjoying music or watching TV at high audio level, we may not be able to hear a telephone ring and thus miss an important incoming phone call. To overcome this situation, the circuit presented here can be used. The circuit would automatically light a bulb on arrival of a telephone ring and simultaneously mute the music system/TV audio for the duration the telephone handset is off-hook. Lighting of the bulb would not only indicate an incoming call but also help in locating the telephone during darkness.
On arrival of a ring, or when the handset is off-hook, the inbuilt transistor of IC1 (opto-coupler) conducts and capacitor C1 gets charged and, in turn, transistor T1 gets forward biased. As a result, transistor T1 conducts, causing energisation of relays RL1, RL2, and RL3. Diode D1 connected in anti-parallel to inbuilt diode of IC1, in shunt with resistor R1, provides an easy path for AC current and helps in limiting the voltage across inbuilt diode to a safe value during the ringing. (The RMS value of ring voltage lies between 70 and 90 volts RMS.) Capacitor C1 maintains necessary voltage for continuously forward biasing transistor T1 so that the relays are not energised during the negative half cycles and off-period of ring signal. Once the handset is picked up, the relays will still remain energised because of low-impedance DC path available (via cradle switch and handset) for the in-built diode of IC1. After completion of call when handset is placed back on its cradle, the low-impedance path through handset is no more available and thus relays RL1 through RL3 are deactivated.
As shown in the figure, the energised relay RL1 switches on the light, while energisation of relay RL2 causes the path of TV speaker lead to be opened. (For dual-speaker TV, replace relay RL2 with a DPDT relay of 6V, 200 ohm.) Similarly, energisation of DPDT relay RL3 opens the leads going to the speakers and thus mutes both audio speakers. Use NC contacts of relay RL3 in series with speakers of music system and NC contacts of RL2 in series with TV speaker. Use NO contact of relay RL1 in series with a bulb to get the visual indication

Two line intercom plus a telephone changeover switch

2010-04-16T23:37:00.000-07:00

Two line intercom plus a telephone changeover switch

The circuit presented here can be used for connecting two telephones in parallel and also as a 2-line intercom.
Usually a single telephone is connected to a telephone line. If another telephone is required at some distance, a parallel line is taken for connecting the other telephone. In this simple parallel line operation, the main problem is loss of privacy besides interference from the other phone. This problem is obviated in the circuit presented here.
Under normal condition, two telephones (telephone 1 and 2) can be used as intercom while telephone 3 is connected to the lines from exchange. In changeover mode, exchange line is disconnected from telephone 3 and gets connected to telephone 2.
For operation in intercom mode, one has to just lift the handset of phone 1 and then press switch S1. As a result, buzzer PZ2 sounds. Simultaneously, the side tone is heard in the speaker of handset of phone 1. The person at phone 2 could then lift the handset and start conversation. Similar procedure is to be followed for initiation of the conversation from phone 2 using switch S2. In this mode of operation, a 3-pole, 2-way slide-switch S3 is to be used as shown in the figure.
In the changeover mode of operation, switch S3 is used to changeover the telephone line for use by telephone 2. The switch is normally in the intercom mode and telephone 3 is connected to the exchange line. Before changing over the exchange line to telephone 2, the person at telephone 1 may inform the person at telephone 2 (in the intercom mode) that he is going to changeover the line for use by him (the person at telephone 2). As soon as changeover switch S3 is flipped to the other position, 12V supply is cut off and telephones 1 and 3 do not get any voltage or ring via the ring-tone-sensing unit.
Once switch S3 is flipped over for use of exchange line by the person at telephone 2, and the same (switch S3) is not flipped back to normal position after a telephone call is over, the next telephone call via exchange lines will go to telephone 2 only and the ring-tone-sensing circuit will still work. This enables the person at phone 3 to know that a call has gone through. If the handset of telephone 3 is lifted, it is found to be dead. To make telephone 3 again active, switch S3 should be changed over to its normal position.

Telephone Ringer using 556 dual timers

2010-04-16T23:25:00.000-07:00

Telephone Ringer using 556 dual timers

Using modulated rectangular waves of different time periods, The circuit presented here produces ringing tones similar to those produced by a telephone.
The circuit requires four astable multivibrators for its working. Therefore two 556 ICs are used here. The IC 556 contains two timers (similar to 555 ICs) in a single package. One can also assemble this circuit using four separate 555 ICs. The first multivibrator produces a rectangular waveform with 1-second low duration and 2-second high duration. This waveform is used to control the next multivibrator that produces another rectangular waveform.
A resistor R7 is used at the collector of transistor T2 to prevent capacitor C3 from fully discharging when transistor T2 is conducting. Preset VR1 must be set at such a value that the two ringing tones are heard in one second. The remaining two multivibrators are used to produce ringing tones corresponding to the ringing pulses produced by the preceding multivibrator stages.
When switch S1 is closed, transistor T1 cuts off and thus the first multivibrator starts generating pulses. If this switch is placed in the power supply path, one has to wait for a longer time for the ringing to start after the switch is closed. The circuit used also has a provision for applying a drive voltage to the circuit to start the ringing.
Note that the circuit is not meant for connecting to the telephone lines. Using appropriate drive circuitry at the input (across switch S1) one can use this circuit with intercoms, etc. Since ringing pulses are generated within the circuit, only a constant voltage is to be sent to the called party for ringing.

Temperature Sensor with Digital Output

2010-04-16T23:18:00.000-07:00

Temperature Sensor with Digital Output

This is a very simple to implement Temperature Sensor. It uses LM35DT as a semiconductor temperature sensor which operates with a +5 volt DC.
It produces an analog output voltage, proportional to the change in surrounding temperature in Celsius scale (2mv/C). The analog output of the sensor is then passed to the ADC0804 IC which produces an 8-bit binary output (digital output) coresponding to the analog input voltage. The digital output from ADC is then used to glow the LED which indicates the high/low logic (LED ON: Logic 0, LED OFF: Logic 1).
The output of the ADC can be interfaced to a 7-segment disply using a 7-segment driver or the digital output can be interfaced to a PC / microcontroller. The bottom portion of the schematic shows a fixed and a variable power supply which inputs 220 volts AC from the wall outlet in your house, the transformer then steps-down it to 18 volts AC (9-0-9 centre-tapped), which is then converted to DC using bridge rectifier.
The fixed regulator IC (7805) produces a +5 volts regulated output which is used to operate the Sensor and the ADC0804 IC. It also outputs a variable voltage controlled by a 5K variable resistor which is used to adjust the scaling of the ADC0804 (normally for full scale, it is set to 2.5 volts).

Light Barrier Detector

2010-04-16T23:12:00.000-07:00

Light Barrier Detector

This simple circuit using a single transistor turns ON the relay when light falls on the LDR.
The potentiometer is adjusted for the required sensitivity.
The power supply is 6V.
Be careful about the impedance of the relay. Its impedance should not be less that 60ohm.
Its working can be explained as follows:
With the light falling on the LDR,its resistance is low and the transistor is saturated and turns the relay ON.
When light is obstructed, the LDRs resistance becomes very high. The potentiometer shorts the transistors
base to ground and it is cut off. Hence the relay is OFF.

Ultrasonic switch

2010-04-16T22:58:00.000-07:00

Ultrasonic switch

Circuit of a new type of remote control switch is described here. This circuit functions with inaudible (ultrasonic) sound. Sound of frequency up to 20 kHz is audible to human beings. The sound of frequency above 20 kHz is called ultrasonic sound. The circuit described generates (transmits) ultrasonic sound of frequency between 40 and 50 kHz. As with any other remote control system this cirucit too comprises a mini transmitter and a receiver circuit. Transmitter generates ultrasonic sound and the receiver senses ultrasonic sound from the transmitter and switches on a relay. The ultrasonic transmitter uses a 555 based astable multivibrator. It oscillates at a frequency of 40-50 kHz. An ultrasonic transmitter transducer is used here to transmit ultrasonic sound very effectively. The transmitter is powered from a 9-volt PP3 single cell. The ultrasonic receiver circuit uses an ultrasonic receiver transducer to sense ultrasonic signals. It also uses a two-stage amplifier, a rectifier stage, and an operational amplifier in inverting mode. Output of op-amp is connected to a relay through a complimentary relay driver stage. A 9-volt battery eliminator can be used for receiver circuit, if required. When switch S1 of transmitter is pressed, it generates ultrasonic sound. The sound is received by ultrasonic receiver transducer. It converts it to electrical variations of the same frequency. These signals are amplified by transistors T3 and T4. The amplified signals are then rectified and filtered. The filtered DC voltage is given to inverting pin of op-amp IC2. The non- inverting pin of IC2 is connected to a variable DC voltage via preset VR2 which determines the threshold value of ultrasonic signal received by receiver for operation of relay RL1. The inverted output of IC2 is used to bias transistor T5. When transistor T5 conducts, it supplies base bias to transistor T6. When transistor T6 conducts, it actuates the relay. The relay can be used to control any electrical or electronic equipment. Important hints:
1. Frequency of ultrasonic sound generated can be varied from 40 to 50 kHz range by adjusting VR1. Adjust it for maximum performance.
2. Ultrasonic sounds are highly directional. So when you are operating the switch the ultrasonic transmitter transducer of transmitter should be placed towards ultrasonic receiver transducer of receiver circuit for proper functioning.
3. Use a 9-volt PP3 battery for transmitter. The receiver can be powered from a battery eliminator and is always kept in switched on position.
4. For latch facility use a DPDT relay if you want to switch on and switch off the load. A flip-flop can be inserted between IC2 and relay. If you want only an ON-time delay use a 555 only at output of IC2. The relay will be energised for the required period determined by the timing components of 555 monostable multivibrator.
5. Ultrasonic waves are emitted by many natural sources. Therefore, sometimes, the circuit might get falsely triggered, espically when a flip-flop is used with the circuit, and there is no remedy for that.

Sound Controlled Filp Flop

2010-04-16T22:44:00.000-07:00

Sound Controlled Filp Flop

Described here is a very inexpensive solution to many phono-controlled applications like remote switching on, for instance, or activating a camera, tape recorder, burglar alarms, toys, etc. The circuit given here employs a condenser microphone as the pick-up. A two-stage amplifier built around a quad op-amp IC LM324 offers a good gain to enable sound pick-up upto four metres. The third op-amp is configured as a level detector whose non-inverting terminal is fed with the amplified and filtered signal available at the output of the second op-amp. The inverting input of the third op-amp is given a reference voltage from a potential divider consisting of a 10k resistor and a 4.7k preset. The 100-ohm resistance in series with the potential divider ensures against the mistriggering of the circuit by noise. Thus by adjusting the preset one can control the sensitivity (threshold) of the circuit. The sensitivity control thus helps in rejecting any external unwanted sounds which may be picked up by the amplifier. The output of the level detector are square pulses which are used to trigger a flip-flop. The 100mF capacitor connected across the supply also helps in bypassing noise.
A well regulated supply is recommended for proper functioning of the circuit because an unregulated supply can cause noise pulses to appear in the supply rails when the circuit changes-over state (especially when a load is connected to the circuit). These pulses can be picked up by the sensitive amplifier which will cause the circuit to again switch-over states, resulting into motor-boating noise.
Since the circuit operates at 4.5V, it can be easily incorporated in digital circuits. Fig. (b) shows how the circuit can be employed to control the direction of a DC motor. The circuit employs four npn transistors. Transistors T1 and T4 have their bases tied together and they switch-on simultaneously when Q output is logic 1. Similarly T2 and T3 conduct when Q output is logic 1. Thus current through the motor changes direction when the flip-flop toggles. Filters connected in the circuit and tuned to different bands of audio frequencies will enable the same circuit to control more than one device. For instance, a high frequency sound (such as whistle) can switch on device 1 and a low frequency sound (such as clapping) can control device 2.

Optical toggle switch using a single Chip

2010-04-09T07:48:00.000-07:00

Optical toggle switch using a single Chip

Using dual flip-flop IC CD4027 employ a 555 based monostable circuit to supply input clock pulses. The circuit described here obviates this requirement. One of the two flip-flops within IC CD4027 itself acts as square wave shaper

Metal Detector

2010-04-09T07:37:00.000-07:00

Metal Detector

The circuit described here is that of a metal detector. The operation of the circuit is based on superheterodyning principle which is commonly used in superhet receivers. The circuit utilises two RF oscillators. The frequencies of both oscillators are fixed at 5.5 MHz. The first RF oscillator comprises transistor T1 (BF 494) and a 5.5MHz ceramic filter commonly used in TV sound-IF section. The second oscillator is a Colpits oscillator realised with the help of transistor T3 (BF494) and inductor L1 (whose construction details follow) shunted by trimmer capacitor VC1. These two oscillators frequencies (say Fx and Fy) are mixed in the mixer transistor T2 (another BF 494) and the difference or the beat frequency (Fx-Fy) output from collector of transistor T2 is connected to detector stage comprising diodes D1 and D2 (both OA 79). The output is a pulsating DC which is passed through a low-pass filter realised with the help of a 10k resistor R12 and two 15nF capacitors C6 and C10. It is then passed to AF amplifier IC1 (2822M) via volume control VR1 and the output is fed to an 8-ohm/1W speaker. The inductor L1 can be constructed using 15 turns of 25SWG wire on a 10cm (4-inch) diameter air-core former and then cementing it with insulating varnish. For proper operation of the circuit it is critical that frequencies of both the oscillators are the same so as to obtain zero beat in the absence of any metal in the near vicinity of the circuit. The alignment of oscillator 2 (to match oscillator 1 frequency) can be done with the help of trimmer capacitor VC1. When the two frequencies are equal, the beat frequency is zero, i.e. beat frquency=Fx-Fy=0, and thus there is no sound from the loudspeaker. When search coil L1 passes over metal, the metal changes its inductance, thereby changing the second oscillators frequency. So now Fx-Fy is not zero and the loudspeaker sounds. Thus one is able to detect presence of metal.

Color Sensor

2010-04-09T07:26:00.000-07:00

Color Sensor

Colour sensor is an interesting project for hobbyists. The circuit can sense eight colours, i.e. blue, green and red (primary colours); magenta, yellow and cyan (secondary colours); and black and white. The circuit is based on the fundamentals of optics and digital electronics. The object whose colour is required to be detected should be placed in front of the system. The light rays reflected from the object will fall on the three convex lenses which are fixed in front of the three LDRs. The convex lenses are used to converge light rays. This helps to increase the sensitivity of LDRs. Blue, green and red glass plates (filters) are fixed in front of LDR1, LDR2 and LDR3 respectively. When reflected light rays from the object fall on the gadget, the coloured filter glass plates determine which of the LDRs would get triggered. The circuit makes use of only AND gates and NOT gates.
When a primary coloured light ray falls on the system, the glass plate corresponding to that primary colour will allow that specific light to pass through. But the other two glass plates will not allow any light to pass through. Thus only one LDR will get triggered and the gate output corresponding to that LDR will become logic 1 to indicate which colour it is. Similarly, when a secondary coloured light ray falls on the system, the two primary glass plates corres- ponding to the mixed colour will allow that light to pass through while the remaining one will not allow any light ray to pass through it. As a result two of the LDRs get triggered and the gate output corresponding to these will become logic 1 and indicate which colour it is.
When all the LDRs get triggered or remain untriggered, you will observe white and black light indications respectively. Following points may be carefully noted :
1. Potmeters VR1, VR2 and VR3 may be used to adjust the sensitivity of the LDRs.
2. Common ends of the LDRs should be connected to positive supply.
3. Use good quality light filters.
The LDR is mounded in a tube, behind a lens, and aimed at the object. The coloured glass filter should be fixed in front of the LDR as shown in the figure. Make three of that kind and fix them in a suitable case. Adjustments are critical and the gadget performance would depend upon its proper fabrication and use of correct filters as well as light conditions

Dew sensor

2010-04-09T07:02:00.000-07:00

Dew sensor

Dew (condensed moisture) ad- versely affects the normal per-formance of sensitive electronic devices. A low-cost circuit described here can be used to switch off any gadget automatically in case of excessive humidity. At the heart of the circuit is an inexpensive (resistor type) dew sensor element. Although dew sensor elements are widely used in video cassette players and recorders, these may not be easily available in local market. However, the same can be procured from authorised service centres of reputed companies. The author used the dew sensor for FUNAI VCP model No. V.I.P. 3000A (Part No: 6808-08-04, reference no. 336) in his prototype. In practice, it is observed that all dew sensors available for video application possess the same electrical characteristics irrespective of their physical shape/size, and hence are interchangeable and can be used in this project. The circuit is basically a switching type circuit made with the help of a popular dual op-amp IC LM358N which is configured here as a comparator. (Note that only one half of the IC is used here.) Under normal conditions, resistance of the dew sensor is low (1 kilo-ohm or so) and thus the voltage at its non-inverting terminal (pin 3) is low compared to that at its inverting input (pin 2) terminal. The corresponding output of the comparator (at pin 1) is accordingly low and thus nothing happens in the circuit. When humidity exceeds 80 per cent, the sensor resistance increases rapidly. As a result, the non-inverting pin becomes more positive than the inverting pin. This pushes up the output of IC1 to a high level. As a consequence, the LED inside the opto-coupler is energised. At the same time LED1 provides a visual indication. The opto-coupler can be suitably interfaced to any electronic device for switching purpose. Circuit comprising diode D2, resistors R5 and R6 and capacitor C1 forms a low-voltage, low-current power supply unit. This simple arrangement obviates the requirement for a bulky and expensive step-down transformer.

Magnetic proximity sensors

2010-04-09T06:36:00.000-07:00

Magnetic proximity sensors

Here is an interesting circuit for a magnetic proximity switch which can be used in various applications.
The magnetic proximity switch circuit, in principle, consists of a reed switch at its heart. When a magnet is brought in the vicinity of the sensor (reed switch), it operates and controls the rest of the switching circuit. In place of the reed switch, one may, as well, use a general-purpose electromagnetic reed relay (by making use of the reed switch contacts) as the sensor, if required. These tiny reed relays are easily available as they are widely used in telecom products. The reed switch or relay to be used with this circuit should be the normally open type.
When a magnet is brought/placed in the vicinity of the sensor element for a moment, the contacts of the reed switch close to trigger timer IC1 wired in monostable mode. As a consequence its output at pin 3 goes high for a short duration and supplies clock to the clock input (pin 3) of IC2 (CD4013 dual D-type flip-flop). LED D2 is used as a response indicator.
This CMOS IC2 consists of two independent flip-flops though here only one is used. Note that the flip-flop is wired in toggle mode with data input (pin 5) connected to the Q (pin 2) output. On receipt of clock pulse, the Q output changes from low to high state and due to this the relay driver transistor T1 gets forward-biased. As a result the relay RL1 is energised.

Super simple stepper motor controller

2010-04-02T09:59:00.000-07:00

Super simple stepper motor controller

The circuit shown above can be used to control a unipolar stepper motor which has FOUR coils (I've swiped it off an old fax machine). The above circuit can be for a motor current of up to about 500mA per winding with suitable heat sinks for the SL100. For higher currents power transistors like 2N3055 can be used as darlington pair along with SL100. The diodes are used to protect the transistor from transients.

Activating sequence:

Inputs Coils Energised

D0 D1

0 0 A,B

0 1 B,C

1 0 C,D

1 1 D,A

To reverse the motor just reverse the above sequence viz. 11,10,01,00.

Alternately a 2bit UP/DOWN counter can also be used to control the direction , and a 555 multivibrator can be used to control the speed

Discrete component motor direction controller

2010-04-02T09:40:00.000-07:00

Discrete component motor direction controller

This circuit can control a small DC motor, like the one in a tape recorder. When both the points A & B are "HIGH" Q1 and Q2 are in saturation. Hence the bases of Q3 to Q6 are grounded. Hence Q3,Q5 are OFF and Q4,Q6 are ON . The voltages at both the motor terminals is the same and hence the motor is OFF. Similarly when both A and B are "LOW" the motor is OFF.
When A is HIGH and B is LOW, Q1 saturates ,Q2 is OFF. The bases of Q3 and Q4 are grounded and that of Q4 and Q5 are HIGH. Hence Q4 and Q5 conduct making the right terminal of the motor more positive than the left and the motor is ON. When A is LOW and B is HIGH ,the left terminal of the motor is more positive than the right and the motor rotates in the reverse direction. I could have used only the SL/SK100s ,but the ones I used had a very low hFE ~70 and they would enter the active region for 3V(2.9V was what I got from the computer for a HIGH),so I had to use the BC148s . You can ditch the BC148 if you have a SL/SK100 with a decent value of hFE ( like 150).The diodes protect the transistors from surge produced due to the sudden reversal of the motor.

Automatic Speed Controller for fans And Coolers

2010-03-29T07:37:00.000-07:00

Automatic Speed Controller for fans And Coolers

During summer nights, the temperature is initially quite high. As time passes, the temperature starts dropping. Also, after a person falls asleep, the metabolic rate of ones body decreases. Thus, initially the fan/cooler needs to be run at full speed. As time passes, one has to get up again and again to adjust the speed of the fan or the cooler.The device presented here makes the fan run at full speed for a predetermined time. The speed is decreased to medium after some time, and to slow later on. After a period of about eight hours, the fan/cooler is switched off.Fig. 1 shows the circuit diagram of the system. IC1 (555) is used as an astable multivibrator to generate clock pulses. The pulses are fed to decade dividers/counters formed by IC2 and IC3. These ICs act as divide-by-10 and divide-by-9 counters, respectively. The values of capacitor C1 and resistors R1 and R2 are so adjusted that the final output of IC3 goes high after about eight hours.The first two outputs of IC3 (Q0 and Q1) are connected (ORed) via diodes D1 and D2 to the base of transistor T1. Initially output Q0 is high and therefore relay RL1 is energised. It remains energised when Q1 becomes high. The method of connecting the gadget to the fan/cooler is given in Figs 3 and 4.

It can be seen that initially the fan shall get AC supply directly, and so it shall run at top speed. When output Q2 becomes high and Q1 becomes low, relay RL1 is turned off and relay RL2 is switched on. The fan gets AC through a resistance and its speed drops to medium. This continues until output Q4 is high. When Q4 goes low and Q5 goes high, relay RL2 is switched off and relay RL3 is activated. The fan now runs at low speed.Throughout the process, pin 11 of the IC is low, so T4 is cut off, thus keeping T5 in saturation and RL4 on. At the end of the cycle, when pin 11 (Q9) becomes high, T4 gets saturated and T5 is cut off. RL4 is switched off, thus switching off the fan/cooler.Using the circuit described above, the fan shall run at high speed for a comparatively lesser time when either of Q0 or Q1 output is high. At medium speed, it will run for a moderate time period when any of three outputs Q2 through Q4 is high, while at low speed, it will run for a much longer time period when any of the four outputs Q5 through Q8 is high.If one wishes, one can make the fan run at the three speeds for an equal amount of time by connecting three decimal decoded outputs of IC3 to each of the transistors T1 to T3. One can also get more than three speeds by using an additional relay, transistor, and associated components, and connecting one or more outputs of IC3 to it.
In the motors used in certain coolers there are separate windings for separate speeds. Such coolers do not use a rheostat type speed regulator. The method of connection of this device to such coolers is given in Fig. 4.
The resistors in Figs 2 and 3 are the tapped resistors, similar to those used in manually controlled fan-speed regulators. Alternatively, wire-wound resistors of suitable wattage and resistance can be used.

Telephone operated remote control using PIC16F84A microcontroller

2010-03-25T00:09:00.000-07:00

Telephone operated remote control using PIC16F84A microcontroller

This design controls up to 8 devices using a PIC microcontroller (PIC16F84A) connected to the phone line. The unique feature here is that unlike other telephone line based remote control, this device does not need the call to be answered at the remote end so the call will not be charged. This device depends on number of rings given on the telephone line to activate/deactivate devices.
Instructions for the telephone operated remote switch:

A) While constructing the main circuit, make sure you use 18pin sockets (base) for the PIC16F84A. Do not solder the IC directly to the board since you may have to remove it for programming. Before you use the PIC on the main circuit, you have to first program it.

B) To program the PIC16F84A microcontroller:

There are lots of programmers on the Internet available to program PIC microncontrollers.
C) Remove the PIC from the programmer socket and put it into the main circuit socket.

Set the DIP SWITCH as follows:

Switch3 Switch4 No. of initial rings to Switch ON(activate half of the board)
OFF OFF 5
ON OFF 4
OFF ON 3
ON ON 2

The number of initial rings to Switch OFF is one more than the number of rings to switch ON. For example, if you have set switch3 OFF & Switch4 ON then number of initial rings to activate half of the board to switch ON the relays is 3 and number of initial rings to activate half of the board to switch OFF the relays is 3+1 = 4.

Switch1 Swtich2 Delay before making the second set of rings
OFF OFF 20sec
ON OFF 15sec
OFF ON 10sec
ON ON 5sec

This is the maximum delay the board can take after it is half activated. It will reset after this delay.
D) Now connect the circuit to the phone line and switch on its power supply.
E) You can test the board now. For example set the DIP switch to Switch1 ON, Switch2 OFF (15 sec delay) & switch3 ON, switch4 OFF (4 rings to activate half for switching ON). If you want to switch ON relay 1 (connected to RB0 of main circuit) then you have to do the following:
1. Give 4 rings and put down the receiver
2. Wait 5 seconds (this 5 seconds wait is required to prevent the board from detecting continous rings)
3. then within 15 seconds give 1 ring (1 ring for relay1, 2 rings for relay2 and so on) and put down the receiver
4. then within 5 sec the relay1 will switch ON
To switch off relay1:
1. Give 5 rings and put down the receiver
2. Wait 5 seconds (this 5 seconds wait is required to prevent the board from detecting continous rings)
3. then within 15 seconds give 1 ring (1 ring for relay1, 2 rings for relay2 and so on) and put down the receiver
4. then within 5 sec the relay1 will switch OFF

Download :

Parts List, C source code complied using HT-Soft PIC C compiler

Alternating Flasher Circuit

2010-03-25T00:02:00.000-07:00

Alternating Flasher

This circuit uses three easily available 555 timer ICs. All three work as astable multivibrators. The first 555 has an on period and off period equal to 1 sec. This IC controls the on/ off periods of the other 2 555s which are used to flash two bulbs through the relay contacts. The flashing occurs at a rate of 4 flashes per second. The diodes are used to protect the 555 ICs from peaks. The relays should have an impedance greater than 50ohms i.e, they should not draw a current more than 200mA. The flashing sequence is as follows:
The bulb(s) connected to the first relay flashes for about 1 sec at a rate of 4 flashes per second. Then the bulb(s) connected to the second relay flashes for 1 sec at a rate of 4 flashes per second. Then the cycle repeats. The flashing rates can be varied by changing the capacitors C3 and C5. A higher value gives a lower flashing rate. Note that the values of C3 and C5 should be equal and should be less than that of C1. The value of C1 controls the change-over rate ( default 1sec). A higher value gives a lower change-over rate. If you use the normally open contacts of the relay, on bulb will be OFF while other is flashing,and vice versa. If normally closed contacts are used, one bulb will be ON while the other is flashing.

Dancing Lights Circuit

2010-03-24T23:56:00.000-07:00

Dancing Lights

Here is a simple circuit which can be used for decoration purposes or as an indicator. Flashing or dancing speed of LEDs can be adjusted and various dancing patterns of lights can be formed.
The circuit consists of two astable multivibrators. One multivibrator is formed by transistors T1 and T2 while the other astable multivibrator is formed by T3 and T4. Duty cycle of each multivibrator can be varied by changing RC time constant. This can be done through potentiometers VR1 and VR2 to produce different dancing pattern of LEDs. Total cost of this circuit is of the order of Rs 30 only. Potentiometers can be replaced by light dependent resistors so that dancing of LEDs will depend upon the surrounding light intensity. The colour LEDs may be arranged as shown in the Figure.

Flashy Christmas Lights

2010-03-24T23:49:00.000-07:00

Flashy Christmas Lights

This simple and inexpensive circuit built around a popular CMOS hex inverter IC CD4069UB offers four sequential switching outputs that may be used to control 200 LEDs (50 LEDs per channel), driven directly from mains supply. Input supply of 230V AC is rectified by the bridge rectifiers D1 to D4. After fullwave rectification, the average output voltage of about 6 volts is obtained across the filter comprising capacitor C1 and resistor R5. This supply energises IC CD4069UB.
All gates (N1-N6) of the inverter have been utilised here. Gates N1 to N4 have been used to control four high voltage transistors T1 to T4 (2N3440 or 2N3439) which in turn drive four channels of 50 LEDs each through current limiting resistors of 10-kilo-o Base drive of transistors can be adjusted with the help of 10-kilo-ohm pots provided in their paths. Remaining two gates (N5 and N6) form a low frequency oscillator. The frequency of this oscillator can be changed through pot VR1. When pot VR1 is adjusted To get the best results, a low leakage, good quality capacitor must be used for the timing capacitor C2

Optical toggle switch using a single Chip

2010-03-24T23:45:00.000-07:00

Optical toggle switch using a single Chip

Audio Light Modulator

2010-03-24T23:37:00.000-07:00

Audio Light Modulator

Audio light modulations add to the enjoyment of music during functions organised at home or outdoors. Presented here is one such simple circuit in which light is modulated using a small fraction of the audio output from the speaker terminals of the audio amplifier. The output from the speaker terminals of audio amplifier is connected to a transformer (output transformer used in transistor radios) through a non-polarised capacitor. The use of transformer is essential for isolating the audio source from the circuit in The sensitivity control potentiometer VR1 provided in the input to transistor T1 may be adjusted to ensure that conduction takes place only after the AF exceeds certain amplitude. This control has to be adjusted as per audio source level. The audio signal Proper earthing of the circuit is quite essential. The diode bridge provides pulsating DC output and acts as a guard circuit between the mains input and pulsating DC output. Extreme care is necessary to avoid any electric shock.

Christmas Star Circuit

2010-03-24T23:28:00.001-07:00

Christmas Star

This circuit can be used to construct an attractive Christmas Star. When we switch on this circuit, the brightness of lamp L1 gradually increases. When it reaches the maximum brightness level, the brightness starts decreasing gradually. And when it reaches the minimum brightness level, it again increases automatically. This cycle repeats. The increase and decrease of brightness of bulb L1 depends on the charging and discharging of capacitor C3. When the output of IC1 is high, capacitor C3 starts discharging and consequently the brightness of lamp L1 decreases. IC2 is an opto-isolator whereas IC1 is configured as an astable multivibrator. The frequency of IC1 can be changed by varying the value of resistor R2 or the value of capacitor C1. Remember that when you vary the frequency of IC1, you should also vary the values of resistors R3 and R4 correspondingly for better performance. The minimum brightness level of lamp L1 can be changed by adjusting potentiometer VR1. If the brightness of the lamp L1 does not reach a reasonable brightness level, or if the lamp seems to remain in maximum brightness level (watch for a minute), increase the in-circuit resistance of potmeter VR1. If in-circuit resistance of potmeter VR1 is too high, the lamp may flicker in its minimum brightness region, or the lamp may remain in off state for a long time. In such cases, decrease the resistance of potmeter VR1 till the brightness of lamp L1 smoothly increases and decreases. When supply voltage varies, you have to adjust potmeter VR1 as stated above, for proper performance of the circuit. A triac such as BT136 can be used in place of the SCR in this circuit. Caution: While adjusting potmeter VR1, care should be taken to avoid electrical shock.

Running Message Display

2010-03-24T23:17:00.000-07:00

Running Message Display

Light emitting diodes are advan- tageous due to their smaller size, low current consumption and catchy colours they emit. Here is a running message display circuit wherein the letters formed by LED arrangement light up progressively. Once all the letters of the message have been lit up, the circuit gets reset. The circuit is built around Johnson decade counter CD4017BC (IC2). One of the IC CD4017BEs features is its provision of ten fully decoded outputs, making the IC ideal for use in a whole range of sequencing operations. In the circuit only one of the outputs remains high and the other outputs switch to high state successively on the arrival of each clock pulse. The timer NE555 (IC1) is wired as a 1Hz astable multivibrator which clocks the IC2 for sequencing operations. On reset, output pin 3 goes high and drives transistor T7 to on state. The output of transistor T7 is connected to letter W of the LED word array (all LEDs of letter array are connected in parallel) and thus letter W is illuminated. On arrival of first clock pulse, pin 3 goes low and pin 2 goes high. Transistor T6 conducts and letter E lights up. The preceding letter W also remains lighted because of forward biasing of transistor T7 via diode D21. In a similar fashion, on the arrival of each successive pulse, the other letters of the display are also illuminated and finally the complete word becomes visible. On the following clock pulse, pin 6 goes to logic 1 and resets the circuit, and the sequence repeats itself. The frequency of sequencing operations is controlled with the help of potmeter VR1.
The display can be fixed on a veroboard of suitable size and connected to ground of a common supply (of 6V to 9V) while the anodes of LEDs are to be connected to emitters of transistors T1 through T7 as shown in the circuit. The above circuit is very versatile and can be wired with a large number of LEDs to make an LED fashion jewellery of any design. With two circuits connected in a similar fashion, multiplexing of LEDs can be done to give a moving display effect.

Automatic Room Lights

2010-03-24T22:52:00.000-07:00

Automatic Room Lights

An ordinary automatic room power control circuit has only one light sensor. So when a person enters the room it gets one pulse and the lights come on. When the person goes out it gets another pulse and the lights go off.But what happens when two persons enter the room, one after the other? It gets two pulses and the lights remain in off state. The circuit described here overcomes the above-mentioned problem. It has a small memory which enables it to automatically switch on and switch off the lights in a desired fashion. The circuit uses two LDRs which are placed one after another (separated by a distance of say half a metre) so that they may separately sense a person going into the room or coming out of the room. Outputs of the two LDR sensors, after processing, are used in conjunction with a bicolour LED in such a fashion that when a person gets into the room it emits green light and when a person goes out of the room it emits red light, and vice versa. These outputs are simultaneously applied to two counters. One of the counters will count as +1, +2, +3 etc when persons are getting into the room and the other will count as -1, -2, -3 etc when persons are getting out of the room. These counters make use of Johnson decade counter CD4017 ICs. The next stage comprises two logic ICs which can combine the outputs of the two counters and determine if there is any person still left in the room or not. Since in the circuit LDRs have been used, care should be taken to protect them from ambient light. If desired, one may use readily available IR sensor modules to replace the LDRs. The sensors are installed in such a way that when a person enters or leaves the room, he intercepts the light falling on them sequentially one after the other. When a person enters the room, first he would obstruct the light falling on LDR1, followed by that falling on LDR2. When a person leaves the room it will be the other way round. In the normal case light keeps falling on both the LDRs, and as such their resistance is low (about 5 kilo-ohms). As a result, pin 2 of both timers (IC1 and IC2), which have been configured as monostable flip-flops, are held near the supply voltage (+9V). When the light falling on the LDRs is obstructed, their resistance becomes very high and pin 2 voltages drop to near ground potential, thereby triggering the flip-flops. Capacitors across pin 2 and ground have been added to avoid false triggering due to electrical noise. When a person enters the room, LDR1 is triggered first and it results in triggering of monostable IC1. The short output pulse immediately charges up capacitor C5, forward biasing transistor pair T1-T2. But at this instant the collectors of transistors T1 and T2 are in high impedance state as IC2 pin 3 is at low potential and diode D4 is not conducting. But when the same person passes LDR2, IC2 monostable flip-flop is triggered. Its pin 3 goes high and this potential is coupled to transistor pair T1-T2 via diode D4. As a result transistor pair T1-T2 conducts because capacitor C5 retains the charge for some time as its discharge time is controlled by resistor R5 (and R7 to an extent). Thus green LED portion of bi-colour LED is lit momentarily. The same output is also coupled to IC3 for which it acts as a clock. With entry of each person IC3 output (high state) keeps advancing. At this stage transistor pair T3-T4 cannot conduct because output pin 3 of IC1 is no longer positive as its output pulse duration is quite short and hence transistor collectors are in high impedance state. When persons leave the room, LDR2 is triggered first followed by LDR1. Since the bottom half portion of circuit is identical to top half, this time with the departure of each person red portion of bi-colour LED is lit momentarily and output of IC4 advances in the same fashion as in case of IC3. The outputs of IC3 and those of IC4 (after inversion by inverter gates N1 through N4) are ANDed by AND gates (A1 through A4) are then wire ORed (using diodes D5 through D8). The net effect is that when persons are entering, the output of at least one of the AND gates is high, causing transistor T5 to conduct and energise relay RL1. The bulb connected to the supply via N/O contact of relay RL1 also lights up. When persons are leaving the room, and till all the persons who entered the room have left, the wired OR output continues to remain high, i.e. the bulb continues to remains on, until all persons who entered the room have left. The maximum number of persons that this circuit can handle is limited to four since on receipt of fifth clock pulse the counters are reset. The capacity of the circuit can be easily extended for up to nine persons by removing the connection of pin 1 from reset pin (15) and utilising Q1 to Q9 outputs of CD4017 counters. Additional inverters, AND gates and diodes will, however, be required.