This circuit serves as an audio output for AM or even FM radios and was found in a Radio Electronics magazine from March 1990. Note the supply voltages.
We found this configuration in an American technical documentation of 1977. The circuit can...
This simple circuit can drive a reed-relay when light falls onto the photo-transistor. The...
In the figure we have the way to obtain an adjustable constant current source of 2 mA. The...