Weird issues controlling a 12V WS2811 LED string with the neopixel node

General
1

Hi all-

I'm developing a museum exhibit using Node-RED, and I'm using the node-red-node-pi-neopixel to control it. Simplified version of the issue: I'm treating the strip as an LED VU meter to display 0-100% of an arbitrary "power level" across 10 LEDs. I have this working very well using a 5V WS2811 string connected directly to the Pi for both 5V power and data from Pin 12 (GPIO18).

When I attempt to connect my 12V WS2811 string that will be used in production (using a tested 12V DC power supply), it behaves very erratically. I made a short video illustrating the behavior. I'm sending the same RGB value for each of the pixels (using the x,y,r,g,b payload format), and you can see from the video that there's a lot of flickering and incorrect colors showing up.

Additional info:

  • I have tested the string with an SP107E connected to the same 12V power supply and everything behaves swimmingly. So I know it's not the strip.
  • My code works properly with a different 5V LED strip, so I don't believe it's the code. For purposes of QA, I did try simply injecting different string payloads into the neopixel node that replicated what I was injecting with code, same behavior.
  • Here is my wiring diagram
  • I've tried both GRB and RGB settings, to no avail
  • I did follow the instructions in this oft-referenced tutorial, including editing /boot/config.txt as specified
  • I did try a different pin for data just to rule that out

Can nny LED wizards out there point me in the right direction?

2

As far as I can tell the data line on these is 5V but the gpio pins are only 3.3V, so I would suggest a level converter to boost your signal to 5V

3

I was starting to come to that conclusion myself. Unfortunately, I can’t seem to find a wiring diagram that shows how to do this with a 12 V strip, only 5 V strips. I do have a bunch of 3.3 V to 5 V converters, but I’m just not sure how to wire it all up. Would you happen to know of a diagram I can reference?

4

Well it depends on converter, but if its something like this -

You provide a common ground, then on LV side 3.3 from the pi and on HV side 5V also the pi.

Then connect gpio pin to LV1 and leds to HV1.

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5

That was exactly what I needed, thank you. It works like a charm now!

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6

In order to help future folks like me, here's a diagram of what worked for me.

This is a 12V WS28xx strip (ignore that the diagram says "+5V" on the strip, this is the only Fritzing part I could find) and external 12V power supply, driven by a Raspberry Pi via the neopixel node in Node-RED. A 3.3V to 5V directional converter was used to get the 3.3V data signal from the Pi to 5V which the strip would understand.

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image1618Ă—1034 251 KB

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7

I use a 74HCT type IC for level converting from 3.3V to 5V, f.i. 74HCT241. Cheap and standard footprint.

1 Like
8

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