so ive been messing around with an arduino mega for the past few weeks trying to get it to control my 6-position antenna switch automatically based on what band the radio is on. the radio is an IC-7300 so it puts out band data on the ACC port which is great, at least in theory.

i got the band voltage decode working mostly fine, like i can read the voltages and map them to bands no problem, but where im running into trouble is the relay switching. im using a 12v relay board i grabbed off amazon and the thing is introducing all kinds of noise on receive. like S2-S3 worth of noise on 40m especially. i tried adding some bypass caps on the relay coil but didnt really help much. im wondering if maybe the relay board itself is just garbage or if theres something else going on.

also thinking about adding a raspberry pi in there somewhere to log which antenna was active at what time for the contest logs but that feels like overengineering it at this point. anyone else gone down this rabbit hole

the relay board noise thing is super common with those cheap amazon boards, the flyback diodes on them are often either missing or installed wrong which causes voltage spikes when the coil de-energizes and that'll get into everything. first thing id do is put a 1N4007 across each relay coil yourself, cathode to the positive side. also make sure your grounds are all tied together properly, a floating ground between the arduino and the relay board will do weird things.

the other thing worth checking is whether your arduino power supply is clean. a lot of guys just use a wall wart and those switch mode supplies can be nasty. i run mine off a small 7805 linear reg off the main shack supply and that made a huge difference for me. the IC-7300 band data is 0-8v depending on band so you should be able to read that directly into analog pins but double check youre not exceeding 5v on any pin or youll have a bad day.

yeah i did almost exactly this setup about two years ago, went through like three different relay boards before i just built my own with proper optoisolation between the arduino side and the relay side. made a huge difference. the pi for logging is actually not that crazy if you have it there anyway, i have mine running a little flask server that my logging software can hit over the local network to pull antenna info. but honestly if your just starting out get the switching working clean first, adding the pi before you have the basics solid just gives you more stuff to debug at once.