I made in 1996 a precision thermostat for controlling an electric heater.

This application uses three integrated circuits: temperature sensor LM335, voltage reference TL431 and operational amplifier LM108, all of them are high precision circuits.

Specification:
- precision thermostat
- 230 VAC command
- adjustable trigger temperature from 20 to 80 °C
- 1.5 °C hysteresis

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Links:
[1] - LM335 datasheet
[2] - TL431 datasheet
[3] - LM108 datasheet