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 is from a 1954 transistors publication. The transistors are the CK722 among the first...
This sophisticated circuit of the coin-toss game was found in an American 1980s documentation. The circuit...
This windshield wiper interval was found in an old documentation. The SCR can be the C106 and the...