Here is a straight forward ,yet effective digital temperature controller that can be used with temperature control systems.
The circuit uses IC LM 35 (IC3) to sense the temperature.The output of LM 35 is given to the IC ADC 0804 (IC4) which converts the analog output of the LM 35 to digital output.The ADC 0804 is a 8 bit ADC .Eight LED’s are connected to the output of ADC to show the output logic.If needed the LED’s can be avoided and the output can be connected to any suitable external circuit like temperature controller etc.A 5V fixed voltage regulator based on 7805 (IC1) powers the circuit.Another variable voltage regulator based on LM317(IC2) is used to provide the reference voltage to the ADC 0804.
Circuit diagram with Parts list.
•POT R10 can be used to adjust the scale factor of the ADC.The reference voltage at pin 7 of ADC0804 should be 2.5 V for full scale.
•Assemble the circuit on a good quality PCB or common board.
•If 1A bridge is not available make one with four 1N 4007 diodes.