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I am working on a small project where I am using a SparkFun Lumini LED Ring. The power supply for the ring is external, connected via its own cable and power adapter. I have connected the ring to the Raspberry Pi using three wires: DI, CI, and GND.

Duo to previous question My LED ring is not working when I connect the GND. I am using a logic level shifter to increase the logic level of my raspi 4 to 5V.

The issue is that the LED-Ring is still not working. I measured the voltage of the LED-Ring and it's 5,3V. The Voltage of Raspi is 3.3V.

The link of the datasheet of the Leds: https://cdn.sparkfun.com/assets/d/c/a/4/2/APA_102-2020-256-6.pdf

the logic level converter that i am using: https://www.amazon.de/Converter-Pegelwandler-BiDirektional-Raspberry-Mikrocontroller/dp/B07DKT9JXT/ref=sr_1_10?keywords=level%2Bshifter%2B3.3v%2B5v&sr=8-10&th=1

the schematic of Leds: https://cdn.sparkfun.com/assets/0/4/2/e/a/LuMini_3Inch.pdf

i connected the shifter as following:

5V of LED - HV shifter - 3,3V of Raspi

GND of LED - GND shifter - GND of Raspi

CI of LED - HV1 shifter - GPIO 18 of Raspi

DI of LED - HV2 shifter - GPIO 21 of Raspi

enter image description here enter image description here it is the same connection but with a LED-Ring

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  • \$\begingroup\$ xcido - Hi, So just to be clear: The wiring diagram must be wrong, because you say that now (after your last question) you have added a level shifter somewhere - but the wiring diagram doesn't show one. || Providing inaccurate information here won't be well-received and may result in fewer answers, or the question may be closed as "needs (accurate) details" etc. So, please, provide accurate information. || I recommend you add a photo of your actual hardware so we can see the wiring. || You're only showing (some) h/w details. But could the problem be with the s/w you're running? TY \$\endgroup\$
    – SamGibson
    Jan 2 at 16:31
  • \$\begingroup\$ Also, do you have access to an oscilloscope, to be able to view the signals from the RPi to the LEDs? If so, please add the scope traces and your analysis of them. \$\endgroup\$
    – SamGibson
    Jan 2 at 16:34
  • \$\begingroup\$ The Amazon page you linked discusses how that level translator will not work with addressable LEDs. Seems like you've confirmed that. A simple 3.3v->5v buffer IC or even just an extra LED pixel right next to the source would be more appropriate. \$\endgroup\$ Jan 2 at 16:37
  • \$\begingroup\$ Oh thank you for you information. I did not notice that the shifter is not compatible with the LED Rings. I will try another one later. \$\endgroup\$
    – xcido
    Jan 2 at 16:45

1 Answer 1

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The level shifter you are using is very slow for this application. You can try this one:

Edit: People are having a problem with this for wires more than a couple of centimetres.

8 Channel Logic Level Bi-directional Converter Module TXS0108E TXB0108

The other solution would be to use 74AHCT125, which Adafruit recommends.

Another solution is to use WS2812 and use them the way that the first pixel is powered with a slightly lower voltage(Image source):

Neopixel

Instead of an ESP module, connect it to Raspberry Pi. Bear in mind this one might not operate properly in all temperatures.

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  • \$\begingroup\$ Why would it work with a 3.3V RPI if it does not work with a 3.3V ESP? They are both still 3.3V. Also why do you suggest the TXB0108 level shifter, as most questions about TSB0108 here are about not getting them working. \$\endgroup\$
    – Justme
    Jan 4 at 23:23
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    \$\begingroup\$ What do you mean by 3.3V? That is only for the first pixel, and it's 4.3v. The next one is 5V. I used TSB0108 with Raspberry Pi before, and it worked fine. I didn't know if people were having a problem with it. I'll have a look. If that's the case, I'll remove that. \$\endgroup\$
    – Saadat
    Jan 5 at 7:59

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