Set any minimum and maximum temperature with the help of LCD display, by pressing switches S2 and S3. The maximum temperature will start from minimum temperature +10 degrees. If the temperature being measured is more than the preset maximum temperature, relay RL1 de-energises and the heating element is switched off. Similarly, when the measured temperature goes below the preset minimum temperature, relay RL1 is energised and the heating element is turned on.
To check the circuit for proper functioning, verify 5V power supply at TP1 with respect to TP0. TP2 is ‘low’when temperature goes below minimum temperature and remains in that state until the maximum temperature is reached.
The author is a B.Tech (electronics engineering) from Dr A.I.T., Bengaluru