The first microcontroller project I started was to add more channels to transmitters for radio-controlled airplanes. The idea was to encode (multiplex) multiple functions into a single channel, then decode the functions into real channels again in the airplane.
The project evolved to also add regular channels, support 16 channels, generate sound or an analog voltage, bootloader, encode PWM to PPM, decode PPM to PWM, custom splicing and advanced mixing of channels and so on. After seven revisions of the hardware, I’ve finally managed to send the board for automated assembling. The finished boards have now arrived. And they work!
Although I still need to do some manual work with each board, this makes the assembly much faster and I can start to sell more of the boards. The firmware is quite advanced so the device deserves a wider audience!