so ive been messing around with this for a few weeks now and i think im close but not quite there. basically i have an old Yaesu G-450A rotator and the controller still works fine but i got tired of manually turning it every time i want to hit a new bearing for satellite passes. figured i could throw an arduino in there and have it handle the positioning automatically based on output from gpredict or whatever.

what i did so far is tapped into the azimuth potentiometer on the controller, running that voltage into an analog pin on a mega 2560 and converting it to degrees. that part actually works pretty well, i can read the current heading within a few degrees which is good enough. the problem is the motor drive side. i was trying to use a relay module to switch the left/right motor lines but im getting these really ugly voltage spikes when the relay clicks and i think its causing the arduino to reset sometimes. put a snubber across the relay contacts and it helped a little but not fully.

anyone dealt with this before? wondering if i should just ditch the relays and go with an optocoupler or maybe a solid state relay setup instead. also not sure if i should be doing the serial comms to gpredict over USB or if i should wire up a proper RS-232 level shifter, the rotctld interface kind of expects real serial ports i think.

yeah the relay spike thing is a classic headache with inductive loads. what youre seeing is back-EMF from the rotator motor kicking back through the relay contacts into your logic. a flyback diode across the coil of the relay itself helps more than a snubber in a lot of cases — make sure youre suppressing on the coil side not just the contact side. i went through something similar with a prop pitch motor setup years ago.

for the SSR route it can work but honestly i just ended up using a small motor driver board, one of those L298N modules, way cleaner switching and you can do soft start which is nice for the rotator bearings. as for the rotctld stuff, i run it over USB with a virtual COM port and it works fine, never bothered with a level shifter. just set the baud rate to match in gpredict and it usually finds it. the hamlib rotator model for the arduino side, there are a few sketches floating around on github that already implement the protocol so you dont have to write it from scratch.

i did something like this with a raspberry pi instead of arduino, mostly because i wanted to run gpredict right on the pi itself and cut out the laptop from the equation. used a pi 4 and one of those cheap ADS1115 ADC boards over I2C to read the pot voltage since the pi doesnt have native analog inputs, which is annoying. the motor switching i handled with a small relay hat designed for the pi so the logic levels all matched up without me having to think too hard about it.

honestly the hardest part wasnt the hardware at all, it was getting the timing right so the rotator would actually stop at the right bearing and not overshoot. had to add some deadband logic, like if youre within plus or minus 3 degrees just stop trying to correct or it hunts back and forth forever. took a few satellite passes of watching it oscillate before i figured that out.