so ive been messing around with an arduino uno for the past few weeks trying to get it to automatically switch between my two antennas based on band in use. the rig is an IC-7300 so i can pull the CI-V data off the USB port and theoretically know what band im on at any given time. my plan is to have the arduino parse the CI-V frequency data and then trigger a relay to flip between my 40m dipole and the trap vertical for 20/15/10.

got the serial comms working mostly fine, the arduino is receiving the frequency data but im having a weird issue where it seems to miss packets every now and then, like itll switch correctly 8 times out of 10 but then just... not respond. no idea if its a timing issue with how fast CI-V polls or something in my parsing code. im using a simple SoftwareSerial setup which maybe isnt ideal.

also the relay im using is just a generic 5v relay module from amazon, wondering if i should be more careful about what relay i use given the currents involved. the coax switch itself is a MFJ-1700C being driven by the relay so its not like im switching RF directly, just the control voltage for the solenoids.

anyone done anything similar? would love to see some code if youve got it

yeah ive done almost exactly this with a 7300, took me a while to get the CI-V parsing reliable. your instinct about SoftwareSerial is probably right — i switched to using a Mega so i had a hardware serial port free for the CI-V side and things got a lot more stable. the timing on SoftwareSerial gets flakey if anything else is happening in your loop, even just millis() calls for debouncing relays can cause it to drop bytes.

also worth checking if you have the CI-V address set right and that transceive mode is on in the 7300 menu, because without transceive it wont broadcast frequency changes automatically and youll have to poll it which is more complicated. with transceive on the radio just shouts out its frequency whenever you turn the VFO and you just listen.

the amazon relay boards are usually fine for switching solenoid control voltages, current is low enough that you wont cook anything. i did put a flyback diode across my relay coil just in case but honestly the MFJ switch solenoids are pretty forgiving.

have you thought about doing this with a raspberry pi instead? not knocking the arduino approach at all but with a pi you can run python and there are already libraries that handle CI-V pretty cleanly, somebody wrote one specifically for icom rigs. then you can add a little relay hat on top and its pretty self contained. also easier to debug since you can just SSH in and print stuff to the terminal while its running rather than dealing with the serial monitor.

just a thought, i went down the arduino road first too and eventually migrated to a pi zero W for most of my shack automation stuff. the arduino is still sitting in a box somewhere