Found in Radio Electronics from the 90s, this circuit uses a thermistor or NTC. The resistance of the thermistor at room temperature can be between 10 and 50k and R3 can have values of the same order.

Found in Radio Electronics from the 90s, this circuit uses a thermistor or NTC. The resistance of the thermistor at room temperature can be between 10 and 50k and R3 can have values of the same order.