Neopixels lighting up 3 at a time???


I have a strip of 150 WS2811 Neopixel LEDs I am running with an Uno and I am using them in a St. Patrick’s day display. I’ve found that if I light up the leds one at a time in order that they turn on 3 at a time. Does anyone know what’s happening here? I am using the Adafruit std. Neopixel library. I copied the sketch to this post. I tried varying the number of leds, the strip type (NEO_GRB also), and the frequency (NEO_KHZ800 also).

#include <Adafruit_NeoPixel.h>
#define PIN 9
uint16_t i;
Adafruit_NeoPixel strip = Adafruit_NeoPixel(150, PIN, NEO_RGB + NEO_KHZ400);

void setup()
  pinMode(9, OUTPUT);

void loop()
for (i = 0; i < strip.numPixels(); i++)
    strip.setPixelColor(i, 0, 255, 0);;    
    Serial.print("i = ");

Is this a 12V strip? If so, the leds are not individually adressable You can only change the colour for groups of 3 leds. If you absolutely need individual control, you need to chose a 5V strip, most of which use ws2812 chips built in to the leds, rather than the ws2811 chips which are separate to the leds.

Yes it is a 12V WS2811 strip, where do you get the info about the 3-at-a-time control limitation? When I first got them there was a control chip at the start of the strip that ran an automatic program. I cut it off and connected to the Uno instead. Actually looking at them I see there is only 1 WS2811 chip for every 3 LEDs so I am very inclined to believe you.

I can't remember, sorry. But it's "common knowledge" among led strip users. You can probably find diagrams on Google which show that each chip drives 3 leds in series.

It is in the data sheet for the WS2811 as an example of a typical circuit.