so ive been messing around with this idea for a while now and finally started putting something together. basically i have 4 antennas — 40m dipole, a vertical for 20/15/10, a loop for 80m, and a random wire i use sometimes for weird stuff — and im tired of manually swapping the coax connections every time i want to change bands. been doing it for like 3 years and honestly its getting old fast.

so i started wiring up an arduino uno with a 4-relay board i grabbed off amazon (the blue ones, you know the kind) and the idea is to tie it into my rig's band data output. my FT-991A puts out band data on the ACC port so in theory the arduino reads that, figures out what band im on, and switches the right relay to connect the correct antenna. sounds simple enough right

the part im stuck on is the logic for reading the band data. its a voltage-coded output i think, different voltages for different bands, and im not sure if i should be using the analog inputs or if theres some cleaner way to handle it. also not sure if i need any buffering between the rig and the arduino, dont want to fry the ACC port on a $900 radio

anyone done something like this? happy to share my code once i get it working, still pretty rough right now

yeah ive done basically exactly this with an IC-7300, the band data voltage thing is straightforward once you look it up in the manual. on yaesu rigs i believe the ACC jack outputs different DC voltages for each band — like 0v for no band selected, then it steps up from there. youll want to use the analog inputs on the arduino and just set threshold values in your code to determine which band youre on. something like if voltage is between 0.8v and 1.2v thats 160m, etc etc.

the buffering question is a good one. i put a simple voltage divider on mine just to be safe, the arduino analog pins are 5v tolerant but the band data output on some rigs can be a little higher than that depending on conditions. a 10k/10k divider brings it down to half and you just adjust your threshold values accordingly. hasnt given me any grief in about 2 years of running it.

one thing i will say — debounce your relay switching in software. when you're tuning around and crossing band edges the thing will chatter like crazy without it. i added like a 500ms delay before actually switching so it only commits once you've been on the new band for half a second. made a huge difference.

might be worth looking at whether a raspberry pi would serve you better here depending on how fancy you want to get with the automation. i built an antenna switcher controller on a pi zero and since it runs linux i can expose a little web interface and switch antennas from my phone or from the logging software via a network call. arduino is totally fine for what youre describing but once you start wanting more integration it can get messy. just something to think about, not saying your approach is wrong at all.