Thanks for your answer. I decided to design my own board based on an OrangePi and obviously your expertise and all you already developed! (I hate Raspberry since the day the SD card crashed and lost all data recorded on it; SD card are definitely not designed for permanent R/W operations).
I prefered to go to I2C (because I’m also curious about this serial bus, I’m from the generation of RX/TX/RTS/CTS … on RS232 :-).
Just another question: could you give me a starting point to understand how to develop the android app. I saw all the source on github but what are you using to design / compile / debug / test such apps ?