so i finally got fed up manually switching between my dipole and the vertical every time conditions change and decided to just build something. started with a basic arduino uno driving a couple relays through a ULN2803 darlington array, nothing fancy, just wanted to be able to flip antennas from the shack PC without walking out to the back of the house.

ended up going way deeper than i planned. now ive got a raspberry pi 4 running a little flask web server that talks to the arduino over USB serial, and i can pull up a browser on any device in the house and switch antennas, check SWR from a little AD8307-based power/SWR detector i wired in, and log which antenna i was using when. the SWR reading part took forever to get right because the RF was getting into everything and i was seeing garbage readings constantly until i put ferrite chokes on basically every wire going into the arduino.

the whole thing cost me maybe 35-40 dollars in parts not counting stuff i already had laying around. anyway just curious if others have done similar stuff and what pitfalls i should watch out for going forward, especially around the RF interference side of things because i feel like im fighting that constantly

yeah the RF getting into the arduino is the classic gotcha with these projects. i spent probably two weekends debugging what i thought was a software problem and it turned out the arduino was just resetting randomly every time i keyed up. ended up putting the whole thing in a grounded metal enclosure and that helped a lot, plus like you said ferrites on everything. also make sure your relay coil suppression diodes are actually installed correctly, i had one backwards once and it was causing all kinds of weird behavior when the relay switched.

the flask web server approach is smart, i did something similar for my rotor controller. one thing that bit me was the serial connection between the pi and arduino dropping out occasionally, so i added a watchdog ping every few seconds and if the arduino doesnt respond the pi tries to reinitialize the connection. saved me a lot of frustration.

35 bucks for an antenna switcher that does SWR monitoring is pretty wild honestly. i priced out a commercial one that does about half of what youre describing and it was like 200 dollars. the RF immunity thing is real, ive heard people running their arduino and pi stuff inside old computer PSU cases because theyre already shielded and have a nice grounded chassis. might be worth trying if you keep having issues