so ive been messing around with an old antenna rotator for a few months now and the controller died on me, the original unit was some no-name thing that came with a used yagi i picked up and honestly the controller was already held together with prayers and electrical tape when i got it. anyway instead of buying a replacement i figured this would be a good excuse to finally do something with the pile of arduino uno and mega boards i have sitting in a drawer from various impulse buys on aliexpress.

the basic idea is to use a stepper motor driver board — i have a drv8825 kicking around — and just drive the azimuth motor directly, reading position back from a pot on the rotator shaft. been looking at hamlib and apparently you can interface custom rotators through rotctld which would be great for getting it working with wsjtx for satellite stuff eventually. i have a raspberry pi 4 that could sit in the shack and handle the higher level stuff while the arduino handles the actual motor control loop.

has anyone actually done something like this end to end? im not worried about the electronics side too much but the hamlib integration is where im getting fuzzy. any gotchas with the serial communication between the pi and the arduino that i should know about going in?

yeah did almost exactly this a couple years back with a create design rotator that the original controller let out the magic smoke on. the hamlib piece is actually not too bad once you wrap your head around it — i used the gs-232 emulation approach, basically just made the arduino respond to the same serial commands that a yaesu rotator controller would, and hamlib already knows how to talk to those. so you're not writing a custom hamlib driver which would be a huge pain.

the pot reading is where i spent most of my debugging time honestly. you really want to average a bunch of analogread samples because the values bounce around more than you'd expect, especially if your motor is running at the same time. i added a small cap on the wiper line and that helped but the software averaging was still necessary. also watch out for the wrap-around logic if your rotator can go past 360, mine could and that caused some weird behavior early on before i accounted for it properly.

the pi to arduino serial thing is pretty much just plug and play, just make sure you set the same baud rate on both ends and dont let anything else grab the serial port before hamlib does. i have mine set up as a systemd service that starts on boot and its been rock solid for like 18 months now pointing at LEO sats.

the gs-232 emulation tip above is the way to go, saves you a ton of headaches. one thing i'd add is think about whether you want to add any limit switches to your hardware setup if the rotator doesnt already have them. i skipped that step and had a bad day when a bug in my code sent the thing spinning past its mechanical stop. nothing catastrophic but it was not a fun afternoon. cheap microswitches wired to interrupt pins on the arduino are good insurance.