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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Micro FM Transmitter (CB20404E)
If the reader is skilled, he can mount this spy micro-transmitter with SMD components and obtain an...
Emitter Follower Detector (CB12236E)
This circuit is suggested by an English publication from 1980. It is an RF detector that uses a...
Light Relay (CB17553E)
This configuration appears in other points of the site both in articles and project suggestions. The...