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.
The supply can be between 4 and 10 V in this circuit and R4 is necessary when the supply is less...
This is an integrated recommended for portable amplifiers, recorders, and battery powered radios. It...
Found in American documentation, this circuit generates linear sawtooth signals using a constant...