4

The CJMCU 8*8 LED board is a grid of 64 W2812 (addressable) LEDs. The board is configured as if it was one long LED strand (just a single DIN, 5v and GND). For some flipping hair pulling reason, my code works fine on 2812 LED strands, but I get nothing on the board. Just random flickering when I jostle the 5V wire. Any ideas? Am I completely missing something here? Pretty sure the board is fine, just can't seem to take any input...

(Here's a link to the board: http://www.aliexpress.com/store/product/CJMCU-64Bit-WS2812-5050-RGB-LED-Development-Board-Built-in-RGB-Driver-White-SKU-11481/933826_32249197598.html)

1

I just received 2 of these from 2 different suppliers on EBAY. None work using the pins called [GND +5V DIN]. As it turns out the DIN is actually NOT DIN. The other connector area [GND +5V DOUT] is the DIN. Ugh!

These boards are marked CJMCU-8*8 on the back side and on the front they say "WS2812B-64 RGB LEDS". Which is another issue. They are using the 6 pin WS2812, not the 4 pin WS2812B.

So if this is what your board looks like then perhaps try the pin marked DOUT for your DIN. Or try to psych out the traces to make sure first.

  • Had the same issue, turned out that DOUT swapped with DIN. Thanks for a hint. – dawidku Jan 15 '17 at 21:42
  • Thanks for the awesome tip about DOUT. I hooked up that one instead and now the matrix works fine. Geez. – VicLovin Feb 13 '17 at 3:39
1

Unbelievably, as I've just discovered, this has been a known issue with these boards for at least a year and a half, yet they are still shipping them. The silk screening process of labeling the board is the problem. Just poor quality control. The front (LED) side of these low quality CMJCU-8*8 boards are incorrectly marked "SM2812B RGB LEDS". (The actual LEDs are 6 pin SM2812's, not 4 pin SM2812B's), but the real problem is with the back side of the board. The manufacturer printed the boards upside down, so that the input and output labels are reversed (DIN is really DOUT and vise versa).

I just purchased one of these defectively printed boards on line and received it a few days ago. Took me awhile to figure out why I couldn't get it to work, but I finally did. When hooked up backwards, the CMJCU-8*8 will do nothing at all (no LEDs will come on), because of the built in reverse polarity protection, but if you run your thumb hard (it's just +5V) over the other pins (the ones that include the erroneously marked DOUT) while the board is powered up, one or more of the SM2812 LEDs will magically come on. This is because your thumb makes an intermittent connection between the real DIN and the +5v rail, providing a forward bias to a few random LEDs. Once lit, these LED's will actually stay on until you cut power to the board, so if you keep ding it, you can get quite a few of the SM2812s to come on.

CMJCU-64 Printing Error

  • My CMJCU-8*8 board is labelled correctly, so try they DIN pin first. – user1491819 Mar 16 '18 at 9:49
  • Hi, I wouldn't have any of the leds come on if this were still the case with my board, right ? I can only get the first two rows (or columns) to light up. They're not lighting up in a way that I would expect if the rest of the LEDS was broken (random colors, random brightnesses, no apparent logic) – oneindelijk Oct 12 at 21:38
  • I just tried it, only one LED will come on, bright blue, somewhere on the third row... – oneindelijk Oct 12 at 21:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.