so ive been messing around with this idea for a while and finally started actually building it. basically i want to use an arduino mega to handle all my antenna switching automatically based on what band the radio is on. i have an IC-7300 and it outputs band data on the ACC port so thats the easy part, already figured out how to read that.

the problem im running into is the relay board. im using one of those cheap 8-channel 5v relay boards from amazon and the coils are pulling enough current that the arduino starts browning out when more than like 3-4 relays trigger at the same time. i think i need to add a separate power supply for the relay coil side but not 100% sure if thats the right fix or if i should be looking at optocoupler isolation or something. the relay board does have opto isolation built in supposedly but honestly not sure i trust the labeling on these things.

also thinking about adding a small 16x2 LCD to show which antenna is selected and maybe the band, nothing fancy. has anyone done something similar? would love to see how other people handled the power supply side especially. dont want to blow up the arduino or worse the radio lol

yeah the cheap relay boards are notorious for that. what you want to do is power the relay coil VCC from a separate 5v supply, not the arduino's onboard regulator. most of those boards have a jumper to separate the relay power from the logic side - look for a little two-pin header near the power input, sometimes its labeled JD-VCC or something like that. you pull that jumper and run your own 5v to the relay coil rail. your arduino logic side stays clean and you stop getting brownouts.

i did almost the exact same project with a 7300 about two years ago. used a nano at first and it was a mess, switched to a mega and its been solid. the band data decoding is pretty straightforward once you get the voltage levels right on the ACC connector - just make sure youre not feeding 5v logic directly into it, use a voltage divider or a level shifter.

the LCD is easy, just do i2c if you can find one of the little adapter boards, saves a ton of pins and its like two bucks extra. whole thing works great, been running it unattended for months without a hiccup.

i did something kinda similar but went with a raspberry pi zero instead of arduino because i wanted to log which antenna was being used and when, and doing that on an arduino is kind of a pain without adding extra storage. the pi made it easy to just write to a file and i can pull up a little web page on my phone to see whats going on. overkill maybe but i had one sitting in a drawer doing nothing.

one thing i'd say is dont underestimate the grounding. had all kinds of weird relay chatter when i first set mine up and it turned out to be a ground loop between the pi and the radio. once i sorted that out it was fine. RF does weird stuff to microcontrollers if you give it half a chance.