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 band changes from my IC-7300. the idea is pretty simple — radio sends CI-V commands out the USB, the arduino reads that, figures out what band im on, and fires the right relay to switch between my yagi and my vertical. on paper it makes total sense but im running into weirdness with the serial timing.

basically what happens is the arduino will catch maybe 3 out of 5 band change commands correctly and then just miss the others entirely. ive tried adjusting the baud rate, tried adding delays, tried using a software serial on different pins thinking maybe the hardware serial was conflicting with something but nothing has really fixed it consistently. im using a level shifter between the radio and the arduino because the CI-V runs at 5v logic and i didnt want to risk the mega's pins.

also considered just ditching the arduino and moving to a raspberry pi zero W so i could run a proper python script with threading and not worry about blocking loops — but that feels like overkill for just switching 4 relays. has anyone actually built something like this that works reliably or am i missing something obvious with the serial handling

yeah i did almost exactly this with my 7300 and an arduino uno a while back. the serial timing issue you're describing sounds like a buffer problem to me — the CI-V output from icom radios can sometimes send incomplete frames if the radio is still mid-transaction when you poll it. what helped me was not trying to parse on the fly but just dumping everything into a ring buffer and then processing it after a short settling delay, like 50ms or so after the last byte comes in. took a bit of fiddling but it got reliable pretty fast after that.

also double check your baud rate actually matches what the 7300 is set to in the menu, i spent like two days chasing a ghost problem that turned out to be the radio was set to 9600 and i had the arduino at 19200. felt pretty dumb about that one.

honestly the pi zero W isnt that overkill for this, i know it sounds like it but once you have python doing the serial stuff it's actually way easier to debug and the threading thing you mentioned is real — blocking loops on the arduino are annoying when you're dealing with timing sensitive serial protocols. i run a pi zero in my shack handling CAT control, a small web interface for remote logging, and a couple gpio lines for PTT and band data all at once and it doesnt even break a sweat. the only downside is boot time if you lose power but you can hack around that pretty easily.