Either solder the LED matrix into place on the backpack, or add some machine pin headers so that you can swap out the matrix as you like.

It's a good idea to pre-assemble all the electronics loosely before gluing everything into place.

Now is a good time to adjust the address settings on each matrix. I found the 0x73 works a treat!

Grab your hook-up wire and create a harness that chains the eyes together and then connects to the Arduino...

Or you can solder the wires directly to the backpack.

Insert each matrix into the eye hole...

And secure with just a touch of hot-glue on the corners.

Double check the wiring.

And pull the ends through the holes in the base of the head.

When you're ready, connect the pins of the eye harness into the Arduino as follows:

• VCC --> VIN
  
• GND --> GND
  
• SDA --> A4
  
• SCL --> A5
  

If you plug VCC into the Arduino 5v line... power to the radio will sag below it's minimum requirement. Alternatively, you could plug VCC directly into your battery source as long as it won't exceed 9 volts.