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.
This circuit was found the Optoelectronics Sourcebook by Texas Instruments. Any phototransistor...
This traditional photodiode amplifier configuration uses an operational one that is no longer...
Figure bellow shows how one of the two separated counters found inside the 4518 is used as a...