Do the sketches on the 2 boards interact with each other at all?
Yes… A little bit… One holds an autopilot that can fly via GPS (Second Board).
(Please do not tell me to go and buy an APM like Arducoter, Flyduino, etc. I want the challenge of building it myself).
The other (First Board) runs a Remote Control Receiver (Yes, instead of buying, I made my own, Arduino in my hands, with a pro joystick, Arduino on the plane and a couple of UHF HC-12 shields between us. Flies over 1km with no problem, no noticeable lag, the responsiveness is impressing).
(Please do not tell me to go and buy a decent pro remote kit for RCs. I enjoyed that much building it myself). (There’s a photo attached to the post.)
This RC project has already been flown dozens of times. It proved itself worthy.
Now I would like to implement my own RTL (“Return To Launch” mode).
The RTL software and sensors live on the Second Board, had to do that, cuz libraries for GPS, Magnetometer, IMU and Barometer, when joint together, plus my own code, have a huge footprint!
The idea is to maintain both boards on the plane. The RC board only turn servo control to the RTL board when a button is pressed on the remote or when radio contact is lost… Hence the idea of using a digital output pin from the RC board to the RTL one. When 5v comes from the RC board in a certain pin of the RTL one, it is a signal that RC board gave up servo control, and the RTL board needs to take over control of servos, until it receives 0v from the RC board again, then it will be time to give up servo control back to the RC Arduino.
Another idea that I considered, consists in “channeling” the servo commands from the RC board to the servos via RTL board. Injecting PWM signal (three servos) to the RTL’s PWM inputs and have them bypassed by software to the servos(connected to the RTL board PWM outputs). When receiving the 5v, the RTL board would ignore its inputs from the RC board and drive the servos by itself.