so ive been messing around with this idea for a while now and finally starting to put it together. basically i have a 4-port antenna switch and i got tired of manually swapping between my 40m dipole, the vertical, and my 2m/70cm colinear every time i change bands. figured an arduino could handle the relay switching if i feed it band data from the radio.

my rig puts out band voltage on the accessory port, different DC voltages for different bands, which is pretty common. the plan is to have the arduino read that voltage through a voltage divider into an analog pin and then trigger the appropriate relay. got a 4-relay module from amazon that seems to work fine in testing with just a battery and some jumper wires.

where im running into trouble is the code side. im decent with hardware but my programming is... lets just say rusty. ive got it reading the voltage and printing to serial monitor but the logic for mapping voltage ranges to relay outputs is kind of a mess right now. also not sure if i need any debouncing or delay logic when switching bands so i dont hot-switch the antenna while transmitting.

anyone done something similar? happy to share what i have so far if someone wants to look at the code. also wondering if a pi would have been a smarter choice since it can run python which id be more comfortable with but the arduino felt simpler for just reading a pin and flipping relays.

yeah ive done almost exactly this, used a nano for mine. the voltage mapping isnt too bad once you just do a big if/else if block with some tolerance on each side of the expected voltage — like if the voltage reading is between 180 and 220 (in raw ADC counts) treat it as 40m, that kind of thing. works fine in practice even if its not elegant.

the hot-switching thing is a real concern though. what i did was add a small delay after detecting a band change before actually firing the relay, like 200ms or so, and also read the PTT line from the radio so the arduino knows not to switch if youre transmitting. you can usually grab PTT from the same accessory connector. took me an afternoon of fiddling but its been solid for like 8 months now. never fried anything.

arduino is totally the right call for this over a pi honestly. the pi boot time alone would annoy you every time you powered up the shack. for something that just needs to read a voltage and flip a relay an arduino is perfect, simpler is better.

dont overlook putting some flyback diodes across your relay coils if that module doesnt already have them built in, most of the cheap amazon ones do but worth checking. inductive kick from the relays can mess with the arduino inputs over time, had that happen on a different project and it took me forever to figure out why things were acting weird intermittently.