Wiring Harnesses

For the sake of troubleshooting and maintenance, I did not want to hard-wire everything together. If a Fadecandy board or something else needs to be replaced, there’s a degree of modularity and hierarchy to the design.

Keeping with the “three groups” motif…three Fadecandy boards, three sets of power terminals…three identical wiring harnesses were built, each distributing power and data to 8 NeoPixel strips. Each block consists of:

  • 1X USB cable
  • 1X Fadecandy board
  • 1X 2-row, 16-pin IDC header and plug
  • 1X 16-conductor ribbon cable
  • 8X JST female receptacle
  • 8X 22 gauge wires for 5V
  • 8X 22 gauge wires for GND
  • 4X 18 gauge wires for 5V
  • 4X 18 gauge wires for GND
  • 1X 12 gauge wire for 5V
  • 1X 12 gauge wire for GND
  • 2X Power distribution bus bars (1 ea. for 5V and GND)
  • Lots of heat-shrink tubing in various sizes (do not use electrical tape)
A 16-pin (8x2) header is soldered to each Fadecandy board.
A mating IDC header is assembled using 16-conductor ribbon cable, sufficiently long to bridge the anticipated distance between the Fadecandy board and strips. Use an IDC crimper or a vise for this. Do not use pliers.

Goal is to get pin 1 of the cable (usually marked with a dark stripe) connected to pin 0 on the Fadecandy board.

IDC cables can be a topological nightmare; accounting for the doubled-back strain relief always gets me.

Examine the header for a pin 1 mark (if any), align this end with pin 1 on the cable and the “0” pin on the Fadecandy board. You may need to try a dummy build and test with a multimeter.
Take one of the JST female receptacles and plug it into one of your assembled strips, tracing back the 5V, data and GND wires. Or if you still have the receptacle from your Arduino testing, use that for reference.

For each receptacle, add an extension to the 5V wire, 22 gauge or heavier. Make sure they’re all oriented the right way, with the key in the same position.
Use a robust inline splice for the connection: twist the wires around each other, solder and cover with heat-shrink.

Take the first two conductors of the ribbon cable and peel away a few inches. The first conductor — pin 1 — gets connected to the data line for strip 0. Slide the heat-shrink tube over the wire before making the inline splice.

The second conductor — pin 2 — then goes to that strip’s GND wire…but, like was previously done for the 5V wires, this wire also needs a 22 ga. extension. It’s a three-way inline splice.

Repeat these steps, peeling pairs of wires off the ribbon cable and connecting to each receptacle’s data & GND wires.

The eight 5V and GND wires all need to meet up with 12 gauge wire to the power supply…that’s 9 wires total, but the power distribution bus bars only accommodate 7 wires each (and don’t take well to doubling-up). So pairs of 5V and GND wires were joined with 18 gauge pigtails (which can handle two strips worth of current) using three-way splices.

Conceptually, it’s similar to this:
Here’s one of the wiring harnesses nearly complete. The 18 gauge power pigtails haven’t yet been added.
The project requires three of these harnesses. It’s really quite laborious. This is why Burning Man folks have soldering parties.

If you have a label-maker, it’s extremely helpful to add strip number “flags” to each JST cable! They need to connect to strips in a specific physical order.
Being a stickler for details, I made these laser cut holders, but you DON’T need to go to such lengths! Fastening everything to a board would work just fine.

Each one holds a Fadecandy board, two power distribution bars (5V and GND) and the wiring harness for 8 NeoPixel strips.
Using a multimeter’s continuity beep feature, do a “sanity check” on each section. There should be no connection between 5V and GND. Also test the data and ground pins on the Fadecandy boards: there should be no shorts between any of the data wires, but the ground wires should all connect.

With no strips attached and with the power supply switched off, each unit was wired in one at a time. Power up, confirm power supply is happy, power down and repeat with the next.
This guide was first published on Aug 11, 2014. It was last updated on Aug 11, 2014. This page (Wiring Harnesses) was last updated on Jul 15, 2019.