so ive been messing around with this for a few weeks now and i think im about 70% of the way there but hitting a wall. basically i have an old Yaesu G-450A rotator and i want to drive it from a raspberry pi 4 instead of the controller box, or at least have the pi read the position and log it automatically during contests.

the position pot in the rotator puts out 0-5v depending on where the antenna is pointing and i thought i could just read that with the pi's GPIO but of course the pi doesnt have an ADC so i ended up grabbing an MCP3008 off amazon and wiring that in. got the SPI talking to it okay and im reading values but theyre really noisy, like bouncing around by 20-30 counts even when the rotator isnt moving. not sure if its a grounding issue or if i need some filtering on the input. tried adding a 0.1uf cap to ground on the input pin and it helped a little but still not great.

the actual motor drive side i havent touched yet, was thinking about using a relay board to trigger the CW and CCW lines but i keep reading about people using H-bridge motor controllers instead. the motor in the G-450A is just a basic AC motor though so i dont think a typical H-bridge is gonna work for that? or am i wrong about that

anyway if anyone has done something similar or has ideas about the ADC noise problem id love to hear it. also open to just using an arduino for the analog side since it has a built in ADC and then talk to the pi over serial, maybe that would be cleaner

the noise on the MCP3008 is pretty typical if you're running it off the pi's 3.3v rail — that rail is surprisingly dirty, especially if you have wifi active on the pi. a lot of people dont realize how much switching noise the onboard wifi throws around. try powering the MCP3008 from a separate regulated supply or at least put a 10uf electrolytic in parallel with that 0.1uf right at the chip's VDD pin. also make sure your AGND and DGND are tied together close to the chip, not somewhere else in the circuit.

on the AC motor question, you're right that a standard H-bridge won't work. those G-series Yaesu rotators use a split-phase AC motor and the controller just switches the phase relationship to reverse direction. a relay board is actually the right approach there, you want DPDT relays to swap the motor leads. just make sure you debounce the switching logic in software and put a small delay between direction changes or you'll get some nasty current spikes. i did something similar with a G-800 and a pi zero a couple years back, worked fine once i sorted the noise issue. i ended up going with the arduino for the ADC side like you mentioned — just cleaner overall and the uno's 10-bit ADC is more than enough resolution for pointing an antenna.

yeah the arduino as a front end for analog stuff and then serial to pi is a pretty common pattern for exactly this reason. i do it for my weather station setup. the pi is great for the network side and logging but the analog IO situation is kind of a pain. one thing though — if youre reading a pot thats tied to a mechanical rotator you might also want to look at whether the pot itself is worn. on older rotators those pots get scratchy and no amount of filtering will fix that, the wiper just has dead spots. might be worth checking if the noise happens at certain positions more than others