so ive been messing around with this for a few weeks now and im not sure if im making it more complicated than it needs to be. basically i have a 4-port antenna switch (the cheap MFJ one) and i wanted to automate it based on what band the radio is on. the FT-991A puts out band data on the ACC port so i figured i could read that with an arduino and drive some relays to switch antennas automatically.

the band data is straightforward enough, its just a few lines that go high or low in different combinations for each band. i got the decoding working fine on the arduino side. the problem is the relay side. im using a generic 8-channel relay board from amazon and i keep getting weird behavior where one relay will sometimes trigger when a different one should. im guessing its a power issue but i honestly dont know. the arduino is powered from USB and the relay board has its own 5v line from a wall wart.

anyone done something like this? feels like im close but also like i could be missing something obvious. also considered just scrapping the arduino and using a raspberry pi with a relay HAT but that seems overkill for what is basically just switching 4 relays.

yeah the relay board thing is almost certainly a ground issue. if your arduino and the relay board power supply dont share a common ground you get all kinds of phantom triggering. also those cheap 8-channel boards are notorious for needing the JD-VCC and VCC jumper dealt with properly — if its jumpered together youre powering the relay coils from the arduino 5v which can brown it out and cause exactly what youre describing. separate the jumper and power JD-VCC from your wall wart, leave VCC connected to arduino for the logic side. fixed that exact problem on a rotor controller i built last year.

and yeah pi is overkill for 4 relays, stick with the arduino. unless you want to add logging or a web interface or something, then maybe, but even then an ESP32 would make more sense than a full pi.

i did something similar with an IC-7300 and a homebrew switch, band data decoding on a nano works great once you get it sorted. one thing i'd add — put some flyback diodes across your relay coils if the board doesnt already have them. the cheap ones sometimes do, sometimes dont. without them youre sending voltage spikes back into the arduino every time a relay opens and eventually that kills the IO pins. learned that the hard way on a project a while back, fried two nanos before i figured out what was happening.