so ive been messing around with an arduino uno for a few weeks now trying to get it to key my FT-891 via the PTT line and i think im overcomplicating this whole thing. basically the idea is i want to run some WSPR transmissions on a schedule without having to babysit the radio, and i also want it to pull the time from a GPS module i had sitting in a drawer so i dont need NTP or anything like that.

the PTT side seems fine, im using a small optocoupler to isolate the arduino from the radio ground which i read is important to avoid loops or whatever. but the timing is where im losing my mind. the GPS module i have is one of those cheap u-blox NEO-6M things and getting it to talk to the arduino serial while also not blocking everything else in the loop is kind of a pain. someone mentioned using the TinyGPS++ library but i cant figure out if that plays nice with the soft serial stuff or if i should just bite the bullet and use hardware serial and give up the USB debug output for now.

anyone done something like this or have a cleaner approach? i feel like there has to be a better way and im probably missing something obvious

yeah the softserial thing will bite you eventually especially if you care about timing accuracy for WSPR since that protocol is pretty unforgiving about being even a couple seconds off. what i ended up doing on a similar project was use a Mega instead of the Uno just so i had the extra hardware serial ports and didnt have to deal with any of that softserial interrupt conflict nonsense. TinyGPS++ works fine but yeah you need it on a real hardware serial port to be reliable.

the optocoupler for PTT is the right call, good on you for doing that from the start. i used a PC817 on mine and it works fine, just watch your current limiting resistor on the LED side. one thing i added later was a small relay after the opto just because i felt better about it for the radio side, probably not strictly necessary but whatever it let me sleep at night.

also if youre doing WSPR specifically you might want to look at the si5351 breakout boards, some people skip the radio entirely for low power WSPR beacons and just use one of those with a LPF. might be overkill for what you want but worth knowing about.

i did almost exactly this last year but with a raspberry pi zero instead and honestly it made the timing stuff way easier since you can just run gpsd and chrony and the system clock stays locked to GPS without you having to manage any of it in your own code. WSPR-X or wsjt-x just runs on a schedule and the timing is solid. the downside is obviously more complexity than an arduino and you gotta deal with linux but if youre comfortable with that it might be worth considering depending on how elaborate you want this to get.