My friend Joe Allen made a rather sizeable relay computer which features a pot you can turn to change the speed in real time: https://hackaday.com/2017/09/18/s

My friend Joe Allen made a rather sizeable relay computer which features a pot you can turn to change the speed in real time: https://hackaday.com/2017/09/18/single-board-relay-computer/ https://hackaday.com/2017/09/18/single-board-relay-computer/ I especially like that it has some relay outputs so you can short basically any electrical item, possibly even an AC mains cable :) and it has numerous inputs and LED display of the internal program counter. I even spent a few hours making a simple drum machine in it once!