so ive been messing around with this idea for a while now and finally started actually building it out. the basic idea is i want the arduino to read the band data output from my IC-7300 and then drive a relay board to switch between my HF antennas automatically without me having to reach over and flip the coax switch manually every time i change bands.

the 7300 puts out band voltage on the ACC connector, different voltage levels for different bands, so thats what im feeding into the analog pins. got a basic sketch going that reads the voltage and maps it to bands okay but im running into trouble with the relay switching — sometimes it bounces between two states when the voltage is in between bands during a QSY and that causes a brief open circuit on the antenna port which im not thrilled about.

thinking i need to add some hysteresis or a debounce delay in the code but not sure what a safe delay would be before the relay actually commits to a new position. also not sure if a brief open during transmit would actually hurt anything or if the rig just sees a high SWR for a split second and the ALC handles it. anyone dealt with this kind of thing before?

yeah i did almost exactly this with a Yaesu FT-991 a couple years back, used the band data from the linear amp jack. the bouncing thing is real and annoying. what i ended up doing was adding a 200ms delay after the voltage reading stabilizes before committing the relay state — basically just compare the current reading to the last reading and only switch if they match for like 5 consecutive polls. works pretty well in practice.

as for the open circuit during transmit, i wouldnt worry too much about a few milliseconds but i wouldnt deliberately design around it being okay either. the 7300 has decent SWR fold-back but its not really meant to handle that repeatedly. i added a small piece of logic that checks a PTT sense line before allowing any switching — that way it just holds the current antenna if youre transmitting and does the switch when you let up. adds a tiny bit of lag but honestly never notice it in normal operation.

the raspberry pi crowd will tell you to do all this in python on a pi zero but honestly for just reading voltages and driving relays the arduino is way simpler and boots instantly which matters if you lose power mid-contest or whatever.

dont stress too much about the open circuit thing, the finals in the 7300 will fold back way before anything bad happens. ive accidentally keyed into a disconnected antenna a few times and its been fine. that said the PTT lockout idea the other guy mentioned is still the cleaner way to do it.

also you might want to look at using a schmitt trigger or just doing it in software with a deadband around the threshold values so if the voltage is like exactly between two expected levels it just stays put. i had a similar noise issue on my analog reads and putting a small cap on the input pin helped a lot too, like 100nF to ground right at the pin.