Build a pushbutton bank without microcontroller
Very common on old equipment, today they seem to have disappeared completely. I am talking about those pushbutton banks of which only one button could be activated at a time, like cassette player’s piano keys or channel selectors on radios. Thanks to a mechanical system pressing one button would release all the others that were pressed (normally only one). Today such tasks are handled by microcontrollers, but this project shows how to do it without. Four relays are switched by four pushbuttons, but only one relay can be on at any time. Add more channels to taste.