Making/Wiring Mono-Pixels

Understanding

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.

• At the led carrier board, all five incoming connections come in on one side and go out the other.
• For consistency, black was used as ground, green as the data line and red the +V line. (While the colors you use really don't matter, it's a good idea to adhere to normal, suggested colors for DC current, if possible, or at least be consistent with your choices.)
• In this example, the blue wire was connected to the "green" channel output of the WS2811 driver board; the white wire was connected to the "blue" channel output.
• At carrier board #1, the LED is soldered across the +V and "green" channel (blue wire, shown with purple lines in the picture).
• All 5 lines would continue on to the 2nd carrier board
• At carrier board #2, the LED is soldered across the +V and "blue" channel (white wire, shown with orange lines in the picture).

• This becomes one completed, 3-led, 3-channel section of the mono-pixel string.
• Notice that only three wires are connected to the WS2811 driver board (far right in the picture); these are the feed wires bringing power and data into the first chip of the mono-pixel string.
• Notice that from the WS2811 driver board to the led carriers, the 5-line wire is used per the instructions above.
• Building the string to the desired length is then as simple as connecting these 3-channel sections together. The order of the boards is DRIVER-carrier-carrier-DRIVER-carrier-carrier-DRIVER-carrier-carrier- etc. Connecting a driver board onto the 2nd carrier board of a section is easy: solder ground, data and power to keep those three lines going to all boards in the string.

• In this example, the strings comprised four WS2811 driver boards and eight led carriers for a total of 12 boards, 12 lights. The total length of the string was 32" and was intended to be inserted into a candy cane. But it was desirable to daisy chain several candy canes together so that they could be sequenced and animated. Therefore, it was necessary to carry the data line through to the next candy cane so that connections could be made at the base of the candy cane.
• The very LAST carrier board of the string included a single wire for the data line that was brought down the candy cane to the base so that a connector could be fashioned to connect to the next candy cane. A thin cat5 wire was used to make the connection.
• The result was a candy cane that required only 12 channels to control (one channel for each led). It's certainly possible to use normal RGB pixels instead, but to produce white, it requires that all 3 channels of each pixel be on, and that's also three times the number of channels required for each candy cane. The mono-pixel string is more efficient in its use of channels.

Construction Tips

Preparing for assembly is an important part of this project.