so ive been messing around with an arduino mega for the past few weeks trying to get it to handle my antenna switching automatically based on what band i QSY to. the idea is it reads the band data output from my IC-7300 (the BCD lines on the ACC port) and then fires relays to switch between my dipole, vertical, and a 6m beam i just put up.

got the relay board wired up and the arduino is reading the band data fine, but im running into this weird issue where the relays are chattering when i first key up. like theres a brief moment where two relays are both partially energized before one fully drops out. not sure if its a timing issue in my sketch or maybe the relay board itself is pulling too much current and browning out the arduino 5v line. using one of those cheap 8 channel relay modules from amazon so that could definitely be the problem.

also been thinking about adding a raspberry pi to the mix to handle logging and maybe do some CAT control stuff through fldigi but not sure if thats overcomplicating things. curious if anyone else has gone down this road and what you ended up doing.

yeah the cheap relay modules will absolutely do that, especially if youre running them directly off the arduino 5v pin. those boards can pull like 70-80mA per relay when they energize and if you have multiple firing at once the voltage sag is enough to cause all kinds of weirdness. what i ended up doing was running the relay coils off a separate 5v supply — just a little wall wart with a common ground to the arduino — and it fixed basically all my chatter issues immediately. also worth putting a small delay in your code between dropping one relay and raising the next, even like 50ms makes a difference.

on the pi question, i do exactly what youre describing and it works great. pi runs flrig as a daemon and the arduino just handles the physical switching side. they talk over serial USB and its been rock solid for about a year now. just make sure your serial baud rates match and you add some handshaking logic or the pi will occasionally send commands before the arduino is fully booted.

the BCD thing from the 7300 is the way to go, ive been doing something similar but honestly i ended up ditching the band data lines and just parsing the CAT commands directly on the pi instead. the arduino still handles the relay timing but it gets its band info from the pi over serial. felt more flexible to me since i can override it from software without crawling under the desk to rewire anything.

one thing i would add — put flyback diodes across your relay coils if that board doesnt already have them. the cheap ones usually do but ive seen a few that dont and the voltage spikes will eventually fry your arduino outputs. learned that one the hard way on a different project, nothing to do with ham radio but same principle applies.