so ive been thinking about this for a while now and i finally started messing around with an arduino uno to control my 6-position antenna switch. the idea is pretty simple i think — use the arduino to read band data from my radio (FT-991A puts out band voltage on the ACC port) and then automatically switch to the right antenna based on whatever band im on

i got the basic relay board working on the bench, just toggling relays on and off with a simple sketch, but im kinda stuck on reading the band voltage reliably. the voltage levels arent always clean and i keep getting false triggers when i transmit. thinking i might need some filtering or maybe an optoisolator in there to keep the RF out of the arduino but honestly not sure where to start with that

anyone done something like this or have a circuit that worked for them? ive seen some stuff online but half of it is for older radios and the pinouts dont match. also wondering if i should just scrap the arduino idea and use a raspberry pi instead since i already have a pi4 sitting here doing nothing — though that feels like overkill for just switching relays

yeah the opto isolator is definitely the right call, RF getting into the arduino will drive you crazy and its hard to debug because it shows up as random weird behavior not obvious errors. i used a PC817 on a similar build for my IC-7300 and it cleaned everything up right away. the 7300 outputs proper logic levels so maybe slightly different situation but the principle is the same

for the band voltage filtering i'd put a small cap across the input too, like 100nF to ground right at the arduino pin, helps a lot with transient spikes during TX. and make sure your ground is solid between the radio chassis and the arduino ground — i had a floating ground issue once that made no sense until i traced it back to that

the pi is overkill for pure relay switching, the arduino is totally fine for this. the pi makes more sense if you want to add logging or a web interface or something but for just reading band data and flipping relays the uno is perfect and simpler to keep running 24/7 without worrying about SD card corruption or whatever

dont overlook the band data from the CAT port if you havent already, way cleaner than trying to read analog voltages. i poll mine over serial every 500ms or so and just parse the frequency out of the FA; response, then my sketch maps frequency ranges to antenna positions. no analog noise to deal with at all

took me an afternoon to get the serial parsing working right but once it did it was rock solid. only gotcha is you gotta make sure the baud rate matches what the radio is set to, i think the 991 defaults to 38400 but double check that