so ive been messing around with an arduino mega for the past few months trying to build something that'll automatically switch between my antennas based on what band im on. right now i have a 40m dipole, a vertical for 15/10, and a G5RV up about 35 feet. every time i qsy i have to walk out to the shack, flip the coax switch manually, and then retune the LDG tuner. its not terrible but i got lazy and figured this would be a fun project.

basic idea is to read the band data from the radio (IC-7300 puts out band voltage on the accessory connector) and then use that to trigger a couple relay modules to switch the coax and also send a retune command to the LDG via its serial interface. ive got the relay part mostly working, tested it on the bench with a 12v supply and the relays click over fine. the problem im running into is the band voltage from the icom isnt quite what i expected — the documentation says like 0-8v depending on band but my multimeter is reading some weird intermediate values and i cant figure out if thats normal or if my analog read on the arduino is just noisy.

also debated switching the whole thing to a raspberry pi zero just so i could have a little web interface to monitor whats happening but honestly the arduino feels more solid for just switching relays, dont really need linux for that. curious if anyone else has gone down this road and has advice on the band voltage thing especially

yeah the band voltage on the icoms can be a little weird, especially if you're reading it on a long wire run or without any filtering. what i did on a similar project was just put a small RC filter on the analog input — like a 10k resistor and a 0.1uf cap to ground — and that cleaned up most of the noise. also worth double checking if there's a pull-down on the accessory jack because sometimes the voltage floats between bands for a second while the rig is switching and you get these garbage readings that confuse the arduino into thinking youre on the wrong band. i added a small debounce in the sketch, just a 200ms delay before acting on a new band value, and that fixed it for me.

the relay module approach is totally fine btw, ive been running something similar for about two years with no issues. i did eventually add a pi zero W to the setup but only because i wanted to log contacts automatically, not because the arduino couldnt handle the switching. for just automating the antenna change the arduino is plenty and honestly more reliable in my experience since theres no OS to hang or update itself at the wrong moment.

dont overthink the pi vs arduino thing, both work. i used a pi for mine because i already had one sitting on the desk but in hindsight the arduino would have been simpler for just relay control. one thing tho — make sure your relay module is optoisolated from the arduino, some of the cheap blue relay boards from amazon will backfeed voltage through the coil flyback and do weird things to the microcontroller. found that out the hard way, fried a nano before i figured out what was going on