NanoPi NEO Adapter - V3
NanoPi is a neat little form factor ARM board with ethernet - or WiFi. See NanoPi NEO, NEO Air, and NEO 2 at www.friendlyarm.com. They can be purchased in the US from andahammer.com. I strongly recommend following their advice and get the heatsink as well.
I built this adapter to bring out my I2C connector as well as to allow DIN mounting without a lot of mechanical fuss; this fits standard 72mm DIN carriers. The NEOs have an odd form factor if one is using the heatsink and a display/buttons. This adapter essentially "flips" the normal NEO orientation so that the heatsink is facing up. The other adapter socket is not flipped so that a stack of boards can be used with a display and/or buttons at the top.
A PCB of the adapter can be ordered from OSHPark. (As of 2018 ~$56US for 3 boards)
The schematic is available here.
The I2C connector is documented at Standard Connector for I2C.
There are two locations for serial connectors, both right angle. One is JST 2.5mm spacing and the other is 0.1".
The I2C connector ~RESET is tied to GPIOG8 (NEO physical pin 16) and ~INTERRUPT is GPIOA6 (NEO physical pin 12).
Important Note about the NEO Socket
Due to the ethernet connector it is necessary to use extra tall sockets for the NEO. They aren't readily available in the sizes needed so I purchased the NanoHAT Proto board that comes disassembled and used those sockets. For the 4 serial pins I justed used a stacking socket extended high enough.
These photos are of a completed unit (not all I2C connectors are populated) that also has a compatible NanoHAT OLED module.