Hi - I'm a fairly experienced hobbyist and programmer,

Hi - I’m a fairly experienced hobbyist and programmer, playing with Neopixels for the first time. I have a very basic setup – an own-design board with 20x SMD WS2812Bs in a single string, driven by a vanilla Uno (which otherwise works fine).

Electrically, I’ve checked that all the LEDs have power at the right pins, that there is continuity between the Arduino data pin and the first DIN, and also from each DOUT to the next DIN. I have a 470uF cap across the 5V supply. Running off USB power: Mac → Uno → LEDs.

Communication Device:

Product ID: 0x0043
Vendor ID: 0x2341
Version: 0.01
Serial Number: 756383030373514112F0
Speed: Up to 12 Mb/sec
Manufacturer: Arduino (http://www.arduino.cc)
Location ID: 0x14200000 / 30
Current Available (mA): 500
Current Required (mA): 100
Extra Operating Current (mA): 0

But, I get nothing, rien, nichts, لا شيئ :wink:

The code is about as pared back as I can make it, borrowed from one of the examples. (NEOPIXEL and WS2812B are synonyms, right ?).


Arduino IDE 1.8.5
macOS 10.13.4

pragma message “FastLED version 3.001.007”

No other compilation errors/warnings

Any ideas for troubleshooting/debugging ?


Two thoughts…where did you buy the “Neopixels”? And have you tried running the Adafruit Strandtest sketch? If you download their library it should be included.

@ob_dev : You never did set the brightness in your setup. Try putting this line in your setup after your line 11:

FastLED.setBrightness(50); // this can be set from 1 to 255

I would change lines 3 and 4 to:

#define DATA_PIN 4
#define NUM_LEDS 20

Also, I would also change line 19 to:


So that the pixels stay on for awhile before it changes to black.

You might want to put a 470 ohm resister between the data out of the Uno and the first NeoPixel data in. I use the two resistor fix (see: First LED frequently burning out on NeoPixels - adafruit industries ) which is similar to this.

Finally, you might want to try the following sketch of mine that I use to test new RGB LED strips and Matrices that I purchase:

It should run on your Uno without any problems since I have run it on a Nano. You just have to change the lines 7 and 9 to your values:

#define DATA_PIN 4
#define NUM_LEDS 20

Did you include capacitors on your board? Each pixel should have a capacitor between +ve and ground…

Thank you all. I must presume it’s a h/w problem: I used a 470R resistor on the end of the DATA_PIN wire and poked around every DIN pad, resetting the Uno each time, but to no avail.

I’ll make up another board tomorrow and attempt not to zap it or overcook it. It’s an own-design PCB with 20x individual LEDs surface mounted on it.

I have a single 470uF across the power rails. This is a test for another project and I did include the 100nF-per-LED on that board.

Just to tie this one up. I did a further rev of the board with all the recommended resistors and caps and it works perfectly. Another datapoint for this technique, if indeed it were needed. Thanks.