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 was obtained in a 1976 magazine. We can use the 555 and another BC548 to generate square...
This circuit was obtained from a 1980's QST magazine. The circuit can generate 1 to 15 MHz signals...
The coils of this simple mid-wave radius are wound 28 or 26 on a 12 to 30 cm long ferrite rod and the...