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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@DrAzzy
+Kalus - have you studied the datasheet (or what passes for one) for the WS2812? http://www.adafruit.com/datasheets/WS2812.pdf
Note particularly the app notes at the end, where we see the critical bypass capacitor (and resistor - though you may not need this), cryptically marked "104", ie, 0.1uf. The point here is to ensure that a high enough voltage remains on VCC to keep the control circuitry alive when it turns on the LEDs, and VDD momentarily drops in response to the sudden increase in current (due to the inductance of the wires). So they put a bypass cap between VCC and ground to filter this effect out, and charge it through a resistor for good measure.
On the WS2812B, they did away with the separate pins for VCC and VDD, and simply put the capacitor between the VCC and Gnd. This makes me think that one could probably get away with omitting the resistor between VDD and VCC on the WS2812 as well.
Maybe in your case the LEDs, running at a lower voltage than intended (I think - there's no spec in the datasheet for VCC/VDD, other than the absolute maximum), are thus drawing less current - enough that the momentary voltage drop isn't resetting it - and that's why it's working at 3.3 - although it's not going to glow as brightly. Do the blues look okay running at 3.3v? That should be the first color to suffer at low voltage. Also, as +Gordon said, you can only run like 2 WS2812's off of the Espruino's +3.3v supply (they're rated at 60ma each full brightness).
That bypass cap IS a real pain if you're hand-wiring up naked WS2812's (which I'm doing as well...)