We found this circuit in the May 1989 Radio Electronics magazine. The circuit can have its values changed to operate at other frequencies and the power supply must be symmetrical.
In the figure we show a timer, this simple one with only one of the four gates of integrated...
This circuit is a sensor for photodiodes that can be used in optical couplers, encoders and other...
This crystal tester was found on a 90s Ham Radio. Transistors are commonly used. The circuit is for...