Hello everyone:

I am not an electronics major, I only have basic knowledge. I need to design a simple on/off circuit controlled by temperature. The amplifier must be built with discrete devices, and the voltage gain must be big enough to activate a 12V relay. I can use a thermistor, temperature sensor (LM35) or RTD. Additionally, one must be able to set the on and off temperature using two potentiometers.

I would really appreciate any help.

Thank you

 

Not fancy, but works. Thermistor simulated with 30k pot.R2 sets heat setting, R1 not needed, R3 resets RY as therm. cools to new set point. A bit tempermental but simpler than making comparators with discreet parts.