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 which band i select on the radio. right now i have a manual coax switch and honestly its fine but i keep forgetting to switch over and then wonder why my SWR is spiking. figured this would be a fun project and also maybe learn something.

the basic idea is to read CAT commands coming off the 7300 via USB, parse out the frequency, and then fire the appropriate relay to connect the right antenna. i have a 4-relay module from amazon thats been sitting in a drawer forever so figured id use that. my question is mostly around the CAT side of things — has anyone done this with an IC-7300 specifically? i found some icom CI-V stuff online but the documentation is kind of all over the place and im not sure if im supposed to be sniffing the serial traffic or if there's a cleaner way to just query the rig directly.

also wondering if i should just bite the bullet and use a raspberry pi instead since it has more horsepower and i could probably find a python library that already handles CI-V. arduino feels more appropriate for the relay control stuff though. maybe both? i dunno, open to suggestions

yeah i did almost exactly this about two years ago, though i was using a 7600 at the time. the CI-V stuff is actually not that bad once you get your head around the address scheme. basically your radio has a default CI-V address (0x94 for the 7300 i think, worth double checking) and you just send it commands over serial and it responds. you dont need to sniff anything, you can actively poll it for the operating frequency.

i ended up going the raspberry pi route for exactly the reason you mentioned — there's a library called pyserial that handles the serial side and then i just wrote maybe 80 lines of python to parse the frequency response and map it to a band. from there i used the GPIO pins to drive a ULN2003 transistor array that switched the relays. worked great. the pi is kind of overkill for just this but it also means you can add a little web interface later if you want, which i did, so now i can see antenna status from my phone which is kind of cool.

the relay module you have should work fine either way. just watch the flyback diodes — the cheap amazon modules sometimes have them, sometimes dont. worth adding them yourself if youre not sure or you'll eventually fry something.

both is a totally valid approach honestly. i use a pi to do the logic and parsing and then it talks to an arduino nano over I2C to handle the actual relay timing and switching. feels cleaner to me, keeps the timing-critical stuff on the microcontroller and the heavy lifting on the pi. bit of extra complexity but once its wired up you forget about it.

one thing i'd watch out for with the 7300 and CI-V is that if you have the USB audio going at the same time for digital modes, sometimes the serial communication gets weird. might just be my setup but its something to be aware of if you plan to run FT8 or whatever while the automation is running.