Triggered Oscillator (CB21252E)

This trip switch circuit was found in a Popular Electronics from the 90's. The frequency basically depends on C1 and R1.

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Simple Relay Shield (CB21223E)
This circuit was found in old American documentation. Transistor is general purpose and relay is...
Simple Alarm (CB25944E)
This simple alarm with latching uses a relay as the main element. The circuit is from a Radio...
Telephone Pickup (CB12308E)
This circuit is from an Italian publication called Fare Elettronica from 1987. What we have is an...