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).
