This circuit detects smoke by changing the light falling on the sensor. The circuit was found in the Electronics Experimenter's Handbook of 1991. Optical devices must be used.
This small amplifier with a low impedance microphone that can be used for hearing aid was found in a...
Found in Popular Electronics, this circuit is intended for testing servos used in model making. The...
This timer circuit was found in a 1980s American documentation. Transistors and SCR support modern...