The sensor of this circuit found in Popular Electronics can be formed by a piece of fabric between two bare wire screens. When wet, the fabric will pass the current between the screens, triggering the alarm.
This sinusoidal oscillator was found in Radio Electronics in 1989. It uses a 741, but other...
This is the circuit of a commercial flash from the 60’s. The circuit was published by the march...
This circuit is suggested by Motorola in its 1990 Linear Databook. The integrated circuit is no...