Up until my current job, my entire career involved physical things. Either doing electronic design, or writing firmware that controlled something or both. The c

Up until my current job, my entire career involved physical things. Either doing electronic design, or writing firmware that controlled something or both. The current day job's not that interesting, so let's talk about the side gig instead. My most interesting product converts position signals from old machine tools (e.g., large planers and mills built in the 70's, 80's and before) into signals that modern motor drives can read. It makes it much easier to retrofit old machinery with modern controls. It was built at the request of a single customer and I did it mainly for fun, but over time it's opened my eyes to the market for tools to retrofit and modernize old equipment. They're still actively buying these from me, but I know there has to be a larger market. Product #2 is still being developed: a generic "leveling module." Basically it's a motor controller designed to keep the load level in one axis. For the last 15 years or so I've also been making modules take a pulse input at one end, and send an accumulated count out the other end over an RS232 serial interface. I don't sell a lot of them, but the surprising thing is that demand hasn't dropped off over all this time. Could probably sell more, but it's really not interesting enough to put a lot of marketing effort into. The fun part is all the customizations I'm asked to do.