Serial RS232 Connection
Since Raspberry Pi outputs work at 3V, but the Paul Ventilation panel uses 12V, a level shifter is required. To keep things simple, I ordered a pre-assembled MAX3232 chip via internet and glued it on my PCB.
To use the serial interface of the RaspberryPi you have to add yourself to the dialout group (and, if the web interface will need access later, the www-data too)
How to utilize minicom and the wiringPi library to talk RS232, I show in hacking RS232.