One of the biggest hassles with addressable LED strip installations is that you usually end up running data and power separately. Sure, in theory, a Neopixel type installation just needs three conductors – one for data, one for ground, and one for +5V or +12V. In practice this doesn’t work on large installations for two reasons:
- If the first pixel is too far away from the controller, the quality of the data signal degrades quickly. After a few feet, you are likely to see glitches.
- You need fairly chunky cables to avoid voltage drop in the power cable. Most LED strips, in fact, have so much voltage drop in the strip themselves that you can only run about 300 pixels before you have to re-inject power.
Last year, I created a big (40′) LED antenna so I could find my way home at Burning Man. I solved the first problem by using differential signaling (RS-422), and the second problem by injecting power every 300 pixels. It looked and worked great:
The trouble was all the cables. I had CAT-5 cables (I used the flat kind) going to each strip with the data, then I used heavy 14awg speaker wire to inject power. As you can see here, the amount of cable (and its complexity) were not insignificant:
I wasn’t really happy with this solution and finally thought, dammit, I’m gonna just run power AND signal over one frigging ethernet cable, I don’t care if you say it’s impossible.
Well, I’m here to report that it’s not impossible. CAT-6 comes with four twisted pairs. I’m using one of the pairs for RS-422 differential signaling. Then I use three of the remaining wires for GND and three for +12V.
I chose CAT-6 because it is available in 23awg, which seems to be the thickest copper you can get in ethernet cabling. At that gauge, there is still some voltage drop. Over about 75 feet, which is the longest you wanna go, you will see a voltage drop from about 12 volts to under 10 volts. That is still within the range that can power a WS2815 strip with 300 pixels happily. I actually plan to plug this into Mean Well power supplies which allow you to juice up the volts to about 13.8 at the origin.
Now, as you can see from the picture of the antenna, my obsession is not having a lot of messy cables or circuitboards up near the base of the LED strips. So I designed this cute little circuit board:
It’s slim enough that you can just heat shrink it and it will basically disappear in between your LED strip and your CAT-6 cable. It has three functions:
- Collect the power from 6 wires and send it to the LED strip
- Decode the differential signal using a MAX485 chip (this is powered using a basic 12V to 5V voltage regulator)
- Three capacitors on the right handle power surges from the LED strip so you can make epileptic flashing white strobes to your heart’s content (not tested).
Here’s a schematic:
These things cost me about $5 each plus shipping to get made in China (including the PCB board, assembly, and all the parts).
In the end I’m psyched that every LED strip in my project will have one simple CAT-6 of exactly the right length going back to my project box!