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.
The circuit shown is from the 1994 Linear Applications Handbook from National Semiconductor. Other...
Found in a 90s Radio Electronics, this circuit is intended to trigger a relay when the current in...
We found this circuit in a 1980 publication. It can be applied to Triacs of the TIC series and the...