Pin mapping on the backside

There exists different versions of the digital expander:

Versions up to 1.2

The first version of the Digital8 Expander has a single line pinstrip with 38 pins.
Pins 1-16 are the jack signals and a GND for each signal.
Pins 17-32 are the break signals and their GND pins. When no plug is inserted in the jack, that signal is breached out to this break-pins.
Pins 33-38 are the SPI interface pins, that you connect to the master module.

This version was mainly created for use when only one expander was supported.

If you want to cascade/chain multiple modules in series with this version, you have to create your own special cables for sharing the 5V, SS and SCK pins from one expander to the next down the cascading line.

Pin Function
33 GND
34 +5V
35 MOSI in
36 MOSI cascade out
37 SS
38 SCK

Version 1.3

This version has more pins in the bottom SPI interface.
The extra added pins are doubles for 5V, SS and SCK. This makes it easy to cascade multiple expanders.

You can use any of the GND-pins as GND-pins for the SPI interface.

Pin Function
33 +5V
34 +5V
35 SS
36 SS
37 SCK
38 SCK
39 MOSI in
40 MOSI cascade out