let us make a thermostat in the room, this circuit energizes the relay when the temperature rises above a specified level. The second series of energy in the relay when the temperature falls below a preset level. Both series are virtually identical. The only difference between them is the polarity of the transistor. Thermistor value is not critical. What matters is the voltage on pin 5 & 6. Thermisto
r any value should work satisfactorily. But you may need to change the value of R1 – to achieve the desired adjustment range.
Do not use “on-board” relay to switch mains voltage. Board layout does not offer sufficient isolation between the relay contacts and low-voltage components. If you want to switch mains voltage – mount relays rated appropriate in a safe place – Away From The Board.