This counter was found in the November 19983 issue of Radio Electronics magazine. The power supply can be between 3 and 12 V typically. The counting speed depends on C1.
This flip-flop controlled by an LDR-type photocell was found in Radio Electroinics magazine from...
This very simple detector uses a hall sensor with a pendulum with a magnet, causing an LED to...
Here is a very useful circuit that can be expanded, including the use of more integrated circuits...