so ive been messing around with an arduino mega for the past few weeks trying to get it to handle antenna switching and also trigger PTT on my IC-7300 when i key up on one of my other radios through a digi mode interface. the problem im running into is the timing is just slightly off, like maybe 20-30ms delay before PTT actually fires and on FT8 that window is tight enough that im dropping the first part of my transmission.

ive got a relay board connected to pin 7 and im using a simple digitalWrite with a small capacitor on the relay coil to reduce the back EMF but i dont know if thats actually helping or making things worse honestly. the code is pretty basic, just watching for a voltage change on an analog pin and then triggering the relay. thought about switching to hardware interrupts instead of polling but havent gone down that rabbit hole yet.

anyone done something similar? also thinking about swapping in a raspberry pi 4 so i could run js8call and handle all the switching logic in python but not sure if thats overkill for what im trying to do

yeah the polling loop is almost certainly your problem. if your loop has any delays in it at all, even a delay(1) somewhere, that adds up fast. switch to hardware interrupts on one of the dedicated interrupt pins, 2 or 3 on the mega, and you'll get your response time down to microseconds instead of whenever the loop decides to check. i did something similar for a remote antenna tuner controller and the difference was night and day.

the cap on the relay coil is fine by the way, thats standard flyback protection, wont cause timing issues. you probably also want a snubber diode across the coil if you havent already, 1N4007 works fine. as for the pi vs arduino question — i run both actually, arduino handles all the real-time stuff like PTT and switching, pi handles the higher level stuff like running wsjt-x and logging. they talk over USB serial. that way you get the best of both, the arduino doesnt care if linux hiccups for half a second

i tried doing everything on a pi 3 once and the latency was killing me too, linux just isnt real time unless you run a RT kernel patch and thats its own whole headache. ended up keeping the pi for the interface and shoved an arduino nano in between for anything timing critical. works pretty well now most of the time. also fwiw the 7300 has CI-V so depending on what youre trying to do you might be able to just send commands directly and not need hardware PTT at all, might be worth looking into