We find this circuit in an old documentation, but it can be made using modern transistors. The circuit trips, producing a continuous sound when the sensor is wet. The 1 mOhm resistor is actually 1 Mohm.
Found in a 90s Popular Electronics, this circuit is based on a common CMOS component. The circuit...
Taken from an Electronics Now from the 90s, this circuit generates signals whose frequency depends on...
This power supply uses a single-winding transformer. We found it in July 1984 Radio Electronics magazine....