> On startup, it'll run the carriage into that switch so it knows exactly where it is. With my setup missing that switch, how does it know where the carriage is? Basically by doing the same thing: it'll run the carriage into the end stop for a good while. If the carriage reaches its limit, it'll slip back and stay there. This gives quite some wear-and-tear on the mechanics and isn't the most elegant solution by a long shot, but for a device that isn't used much and with me not having enough GPIOs left to hook up switches, it had to do.

As I understand it, this is basically the same solution the Apple II disk drives used to return the head to track zero. Owners of the Disk ][ will remember the loud repetitive clicking sound it made at startup. That's the sound of the drive controller moving trying to move the head outward 40 times and hitting the end stop most of the time.