so ive been messing around with this idea for a while now and finally started actually building it out. basically i have 4 antennas - a vertical, a 40m dipole, a 2m yagi, and a random wire thing i threw up last year - and im tired of going out to the shack and manually flipping the coax switches every time i want to change bands or configurations. its getting old especially in the winter.

my plan is to use an arduino mega i had sitting in a box (originally bought it for some other project that never happened lol) and wire it up to a bunch of relay modules to control the antenna switching. the idea is i can either hit a button on a little panel i build, or eventually tie it into my logging software somehow so it switches automatically based on what band im on in the radio.

ive got the relay modules, got the arduino, got a 12v power supply im going to tap off. my concern is RF getting back into the arduino through the relay coils or the control lines and messing everything up. read some stuff about using optoisolators but honestly im not totally sure where that fits in the circuit. also wondering if i need to shield anything or if thats overkill for HF power levels - im running maybe 100 watts on a good day.

anyone actually built something like this? curious how you handled the isolation side of things and whether the arduino survived long term haha

yeah i did basically exactly this about two years ago, used a Nano instead of a Mega but same idea. the RF isolation thing is a real concern, i fried two relay modules before i figured out what was going on. what i ended up doing was running the control lines through ferrite beads - just a couple wraps through a small toroid - and that cleaned things up a lot. also made sure the ground between the relay board and the arduino was solid, floating grounds were causing me weird issues where relays would chatter for no reason.

the optoisolator idea is good if youre going to run longer cable runs between the arduino and the relay board, but if theyre sitting right next to each other on the same little pcb or in the same enclosure, the ferrite approach is probably fine. i also put a 0.1uF cap across each relay coil just for the transient spikes, standard stuff.

mine has been running for like 18 months now with zero issues, handles 100w no problem. the relay contacts themselves matter more than the control side - make sure youre using relays rated well above what youre actually switching. i use DPDT relays rated at 30A for the RF path even though im never coming close to that, the derating at RF frequencies is real and people underestimate it.

i looked at doing something similar but ended up going with a Raspberry Pi instead because i wanted a web interface i could hit from my phone or tablet in the house. runs a little flask server, dead simple. the downside is boot time obviously - arduino wins there if you need it up instantly when you flip the shack power on. for my use case i dont care, the pi is on all the time anyway running other stuff.

one thing ill say is dont underestimate how annoying the software side gets once you start wanting it to talk to your logging program. ive been trying to get mine to read the band data from N1MM and its kind of a rabbit hole depending on what radio you have. some rigs spit out band data over serial nice and clean, others you gotta poll them which adds latency. just something to think about before you go too far down that road