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 1980s documentation, this circuit detects when the voltage drops below 11 V. Other...
This is a commercial circuit from a Japanese publication from 1972. The circuit uses a FET that...
In this circuit we show how to modulate the pulses produced by a 555 in frequency. The circuit can be...