Making/Wiring Mono-Pixels

This is a tutorial on how to make a pixel string manually with regular, single-color LEDs instead of 3-color RGB LEDs. It's a rather labor-intensive project but once finished, the result is quite rewarding and along the way, you'll acquire worthwhile knowledge on how pixels work. You'll also acquire much-improved soldering skills!

To get started, let's understand how the pixel driver board works and how to wire it. At 5/16" wide and 1/2" tall, the driver board is quite tiny and consequently can be a bit testy to work with. This is the same driver board that's in most RGB bullet pixels and uses a single WS2811 chip. The top and bottom sides of the board are shown below along with the assignment of connections. This tutorial will use the 5vdc version of the driver board; pixels that use 12vdc use a variant of the same board but the differences are only to accommodate the larger voltage -- the same concepts presented here apply to the 12vdc version. The WS2811 chip has internal circuitry to serve as a constant-current driver that delivers 18.5ma of current to the three outputs; each chip requires three different channels to control its three outputs.

• The four holes along the top of the board are for the four pins of a common-anode RGB led; the LED is soldered directly into these holes.
• Because the led is a common-anode type, switching is done by taking the output control pins to ground, thereby completing the circuit and allowing each respective led to light up.
• Except for the data in and data out connections, the top and bottom side of the driver board share the same connections.
• The bottom side is clearly marked with an arrow to show the direction of data flow into the chip on the center pad.
• Data is passed through the chip via the data out pad on the top side of the board.
• On a normal RGB pixel, three wires connect to the bottom side as "incoming power and data" and another three wires are connected to the top side of the board as "outgoing power and data" so that the wires can continue to the next pixel. These wires are often colored to help identify the wires but they may all be one color. In such cases, you must study the pixel carefully to try to read which wire is for which connection because the power and ground must be correct and the data must flow according to the arrow on the first pixel of a string; any other order won't work and may damage one or more pixels in the string.

• To create a mono-pixel string that has only one color (white in this example) yet use all 3 channels of each WS2811 chip, one solders a white LED in place of the red, and then carries the green and blue outputs to two more blank "carrier boards" where the 2nd and 3rd leds will be mounted. Further, the power, ground and data lines must also be brought forward to that the LED in the carrier boards can light as well as feed the next WS2811 chip in the string.
• A five-conductor cable is required; suggested types are colored ribbon cable or cat5 cable to help keep the connections consistent.