In a September 1992 Radio Electronics article, we found this basic 555 circuit used to generate fixed times. Capacitor C1 and resistor R1 determine the time. The circuit drives an LED.
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...