so ive been messing around with an arduino mega for the past few weeks trying to build an automated antenna switcher for my shack. the idea is pretty simple — i have a 40m dipole, a 20m wire vertical, and a fan dipole for 10/15m, and i want the rig to just... pick the right antenna based on whatever band i dial in on the IC-7300. i figured i could read the CI-V bus output from the radio and have the arduino interpret the band data and trigger the appropriate relay.

turns out CI-V isnt quite as plug and play as i thought, at least not with a 5v arduino. had to build a little level shifter circuit because the logic levels dont play nice. got that sorted eventually but now the relay switching is introducing some weird RF into the audio chain and im not sure if its the relay itself or just crappy wiring on my part. using a SainSmart 8-channel relay board which maybe wasnt the best choice in hindsight.

anyway the question is has anyone gone down this road and actually ended up with something reliable? or am i better off just buying one of those commercial band decoders. feels like ive learned a lot but im not sure the end result is going to be cleaner than just flipping a coax switch by hand honestly.

yeah the relay board RF issue is almost certainly your wiring. those cheap sainsmart boards have no suppression on the coil side at all, you need a flyback diode across each relay coil or you get nasty transients every time the coil switches. i know everyone says just slap a 1N4007 across it and call it done but on a radio bench that noise can get everywhere depending on how your grounds are laid out.

the CI-V level shifting thing is real, glad you got that figured out. i did something similar with a 7600 a few years back and ended up using an optocoupler instead of a resistor divider, way cleaner isolation especially if your ground loops are sketchy which they usually are in a shack with multiple pieces of gear.

as for whether its worth it — i think it depends on how much you want to learn vs how much you just want a working switcher. if you want the latter just get a microHAM or a band decoder from Array Solutions and be done with it. if you enjoy the tinkering then yeah keep going, once you get it dialed in its satisfying as heck and you can customize it in ways the commercial boxes dont let you.

i built almost exactly this with a Pi Pico actually, not an arduino, but same idea. the pico is nice because you get two cores and can dedicate one to just watching the CI-V traffic without it interfering with the relay switching logic. not sure if that matters much at the speeds were talking about but it felt cleaner to me.

one thing i'd say is dont underestimate the grounding. spent probably two weekends chasing RF in my audio and it turned out the relay board ground wasnt tied to the chassis ground. once i sorted that out most of the noise went away. also put the relay board in a small metal enclosure, that helped too.