so ive been sitting on this idea for a while now and finally started messing around with it last weekend. basically i want to use an arduino mega to replace the control box on my old CDE Ham-IV rotator. the stock controller works fine but its analog and i want to be able to drive it from my PC for satellite work, maybe tie it into gpredict eventually.

i found a few projects online that use an H-bridge to drive the rotator motor and read the azimuth pot with one of the analog pins, which seems straightforward enough. my concern is the pot in the Ham-IV puts out something like 0-500 ohms across the full rotation and im not sure how to scale that properly to get accurate readings — do i need a voltage divider or can i just wire it straight into the analog input? i know the arduino ADC wants 0-5v so im guessing i need to condition the signal somehow.

also thinking about adding a Raspberry Pi 4 to run a web interface so i can control everything from my phone when im out in the garage. has anyone stacked a pi and arduino together for something like this? seems like the pi handles the high level stuff and the arduino does the real-time motor control, which makes sense to me but maybe im overcomplicating it.

yeah done almost exactly this with a T2X rotator a couple years back. the pot thing — you definitely need a voltage divider, dont wire it straight in. what i did was put a 1k resistor in series with the pot and then tap the wiper through another resistor to ground to form a proper divider that keeps everything under 5v. you'll want to map() the ADC readings in your sketch to get degrees out, takes a bit of calibration but once its done its solid.

the pi + arduino combo works great for this kind of thing. i run hamlib on the pi side and have a small flask app that exposes an endpoint, arduino just listens on serial for azimuth commands and sends back position. latency is completely fine for satellite tracking, gpredict talks to hamlib and the whole chain works. only gotcha is make sure your serial baud rate is high enough and you flush the buffer properly or you get stale position readings which will drive you nuts trying to debug.

the Pi and Arduino combo is probably more than you need honestly but it does make the web interface part way easier so i get why you'd go that route. one thing i'd throw out there — if the Ham-IV motor is the original one those things can pull a fair bit of current when starting up so make sure whatever H-bridge you're using is rated for it. i fried a L298N module the first time i tried something similar, those little blue modules off amazon are not as robust as the datasheet implies. went to a Pololu high-current driver after that and no more problems.