so ive been thinking about this for a while and finally started messing around with it last weekend. basically i have a 4-port antenna switch out in the shack and im tired of walking over to flip it manually every time i change bands. figured an arduino could handle reading the band data output from my radio and switching the relays automatically.

the radio puts out BCD band data on a DB9 connector, ive already confirmed the voltage levels are TTL compatible so that parts straightforward. my plan is to use a Mega since i have one sitting around, read the BCD lines, decode the band, and fire the appropriate relay through a ULN2803 driver board i pulled off an old project. the relays are 12v so thats fine, just need to level shift the 5v logic side if im driving anything directly.

what im not sure about is whether anyone has done something similar and run into weird timing issues with the band data. my radio apparently has a brief glitch on the BCD lines during band changes and i dont want the arduino catching it mid-transition and switching to the wrong antenna for half a second. thinking i need to debounce in software but honestly havent thought it through completely yet. anyone dealt with this or have a sketch i could look at as a starting point?

yeah ive done almost exactly this with an IC-7300 and a homebrew 6-port switch. the glitch thing you're worried about is real, my first version would occasionally flicker the wrong relay during a band change and i could actually hear a pop in the audio. what ended up working for me was just a simple timer debounce in the main loop — basically i read the BCD state, wait like 50 milliseconds, read it again, and only act if both readings match. works perfectly now and the delay is so short you dont even notice it operationally.

one thing i'd add is put some protection diodes across your relay coils if the ULN2803 board doesnt already have them. the flyback voltage can do weird things to the arduino over time, might not kill it immediately but ive seen people have flaky behavior traced back to that. also worth putting a small cap on the 5v rail near the arduino if youre switching a lot of relays — the current spikes are real.

i went down this rabbit hole last year and ended up switching to a Raspberry Pi instead of arduino just because i wanted to add a web interface so i could control it remotely too. ended up way more complicated than i planned lol but it does work. if you just need local automation the arduino approach is totally fine and probably more reliable honestly since theres no linux to hang on you.

one thing to think about — do you want manual override? i added a physical rotary switch that can bypass the whole arduino thing in case something goes sideways during a contest or whatever. saved me a few times when i was updating firmware at a bad moment