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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Digital PLL (CB5290E)
We find this circuit in a 1976 NASA handbook. The circuit can be designed based on current logical...
Manual Siren (CB13035E)
In the circuit shown in the figure when we press S1, capacitor C1 charges slowly, and with that it...
4 W Amplifier (CB6281E)
This circuit is from a 1968 Motorola power circuit manual. The circuit uses transistors of the...