Relays up to 100 mA can be driven by the 555 with the recommended circuit. The circuit is from an article in the September 1992 Radio Electronics magazine.
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...