This circuit was found in a Popular Electronics from the 90s. It is based on components still common today and an optical coupler for the triac. The sensor is a thermistor.
Using the CA3140 in the figure we have a comparator that goes low in the window voltage space. The...
This circuit is found in a 2011 technical publication from Texas Instruments. It is an amplifier for...
In this circuit, the LED lights up when the current is such that multiplied by the resistor value...