Those instructions are for the rev 1.0 portable unit, the current prototype I already assembled and tested.

Preparation

PCB order

Order the PCBs from your favorite fabhouse. Everything you need is in SchemBrdDesigns.zip

I personally used dirtyPCBs; you'll find the zip file I sent in the "gerbers" folder.

3D printing

3D-print the three components of the case: the main body, the bottom lid and the D-pad. I used 25% infill, no raft nor supports.

Components order

Order the different components. It should be pretty straightforward.

The CC1101 modules I used came from here: RF1101 eBay. You can use any other module, just make sure they follow the same pin logic.

The SSD1306 OLED display has to be the I2C version.

PCB assembly

Solder the components to the PCB, as per the schematics.

My advice would be to start with the microcontroller side: it's the hardest side to do... Don't forget to solder the radio module header before the display!

Complete assembly

Insert the D-pad in the main body, check the fit: it should be pretty lose and allow the pad to move up and down easily.

Slide the main PCB in the case. Finish by connecting the radio module and snapping the lid on the case. Everything should be held tightly, pressing the D-pad shouldn't move the PCB.

Programming & testing

Re-open the case, plug in a AVR programmer (Arduino as ISP, TinyISP, ...) and flash a bog-standard Arduino Uno bootloader (more info about this process can be found here).

Disconnect the programmer. Connect a micro-USB cable from the Waffle to the computer. It should list itself as a CH340 device. Drivers for Windows can be found here if they don't install themselves on first go.

Use the Arduino IDE to upload the sketch (contained in the "POC Code" zip folder) to the Waffle.

Obviously, you need to build at least two Waffles to test them out. As an alternate solution, you can always use a simple Arduino board (with the same sketch as the Waffle) connected to a CC1101 module (refer to the schematics for more details) as a transmitter.

Messages can be simply sent through a serial monitor (like PuTTY). Baud rate is 9600.