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View Full Version : Strange WS2812 NeoPixel backfeed current. FYIO



t3andy
10-20-2013, 02:55 PM
In one of our designs, we used 13 NeoPixels. With none of the NeoPixels "on", the current draw
was about 10 mA. To eliminate this current consumption, from our battery operated Teensy 3 design,
we had to use a 2N3904 NPN driver transistor on the ground return leg. You could have also used a 2N3906 PNP transistor
on the +5 VDC supply. In both cases the 10 ma. current did not disappear due to a "backfeeding return" through
the NeoPixel driver pin from the Teensy 3. We also installed a series diode, with the cathode pointing to the NeoPixel, and with both the diode and the transistor driver fixed the 10 mA. backfeeding problem.

Hope this helps anyone using WS2812 NeoPixels in a battery operated design.:cool:

On another design note ... Sparkfun has a sealed 1 meter IP65 waterproof WS2812 NeoPixel strip.
Add a Teensy 3 and some special interface "drivers" and you could have the coolest and best bicycle
night-time lighting and warning indicators. Since the Teensy 3 can now be put to sleep
at around 250 uA then the only design issues would be the 60 mA "off current" of the NeoPixels
and the heavy duty power pack to drive them.

https://www.sparkfun.com/products/12027

Letitflow
12-12-2014, 03:54 PM
Hello t3andy,

I am using a Neopixel24 Ring in my Arduino Project and have the same problem you described above. With the 24 pixels "off" there is still a ~15mA current draw.

I am relatively new to microelectronics and do have a few questions regarding the transistor and the diode.

Would this diode be a diode i could use? (max current draw of the Neopixel Ring is 50mA) http://www.produktinfo.conrad.com/datenblaetter/125000-149999/140641-da-01-ml-DIODE_LL4148_SOD_80C_MINIMELF_de_en.pdf

The ring is connected to from PWR->3,3v , G-> GND and IN --> Digital Pin 6 of the Arduino.
How would i connect the diode? Between the Data in and Digitalpin of the Arduino with the cathode pointing to the data in ?
How would i connect the transistor if i buy the 2N3904 NPN?

I would really appreciate any help. Thanks in advance!

Best Regards,
Letitflow

nlecaude
12-12-2014, 08:02 PM
It's normal for neopixels to draw current even when they don't emit light, the chip inside is still listening for data and needs power....

t3andy
12-13-2014, 12:29 AM
@Letitflow
Check this link out and look at the rev 2 schematic at the very bottom of the page.
http://forum.pjrc.com/threads/24319-NeoPixel-Teensy-3-Green-AC-Mains-Clock-Project-The-greenest-AC-Mains-Clock-in-USA!?highlight=neopixel+clock
We used a 1n4001 (D1) diode with the 2n3904 transistor to reduce the current draw for battery operation.

Letitflow
12-14-2014, 02:42 PM
@Letitflow
Check this link out and look at the rev 2 schematic at the very bottom of the page.
http://forum.pjrc.com/threads/24319-NeoPixel-Teensy-3-Green-AC-Mains-Clock-Project-The-greenest-AC-Mains-Clock-in-USA!?highlight=neopixel+clock
We used a 1n4001 (D1) diode with the 2n3904 transistor to reduce the current draw for battery operation.

Thank you very much, very helpful schematic!