Freezing sensor (CB21288E)

This circuit was found in a Popular Electronics from the 90's. The components are common. The potentiometer adjusts the circuit's trigger point.

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Microphone Amplifier (CB12896E)
This counterphase circuit is from a 1973 publication, and can work with mains voltages or 12 V....
Digital Switch (CB17220E)
This circuit can be used to directly control direct current loads or higher alternating current loads...
AD converter for data acquisition (CB12781E)
The acquisition of data, from a transducer, so that these data can be converted to digital form...