The important thing now: how do i set up the backplane bus?

I decided to use DIN 41612 type C connectors with 32 pins (VG32, columns a and c). I could get them from work and already worked with them (same connectors on the FMAS). I placed the 5V and 9V on 1ac and 3ac with GND on 2ac and 4ac. The symmetric voltages were placed at 13ac (+12V) and 15ac (-12V) with GND at 14ac and 16ac. This is to spread out GND for less localized load. I also used two pins for each voltage since every pin could take 1A, so i got 2A for everything.

The rest of the bus pinout grew with the mainboard. As processor I used an Arduino MEGA board which I had on hand. I put it piggiback on the pcb and got every pin on an additional pin header. This way I could easily connect the 3.2″ TFT display with touchscreen. For ease of programming I put a USB connector onto the frontpanel as well as a reset button.

After most of the pins of the Arduino MEGA were used, i pretty much put the rest on the Bus. 5a and 5c are the I2C lines for general communication. 6a and 6c are used for RS232 communication (Rx Tx) as well as 7a and 7c (Rx1 Tx1). You know, just in case. Next are 4 analog inputs for the Arduino MEGA followed by 6 digital pins.

All pins on the bus were equipped with 4k7 Ohm pullup resistors.

ac
15V5V
2GNDGND
39V9V
4GNDGND
5SDASCL
6TX1RX1
7TX2RX2
8A0A1
9A2A3
10D8D9
11D10D11
12D12D13
13+12V+12V
14GNDGND
15-12V-12V
16GNDGND

And here are layout and finished pcb:

And here is the finished module