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 circuit shows how to control an astable configuration using the 555 IC. The control signal is...
This continuity tester for low resistances was found in an English magazine from 1978. The circuit...
This 1995 circuit uses an audio amplifier that is no longer common today. However, other...