WS2812 done right

The rainbow pixels are the Bitsy's flashiest subsystem and its most instructive: eight full-colour LEDs, one GPIO. Each WS2812 pixel contains its own driver chip; data enters the first pixel at 800 kHz on a single wire, the pixel keeps its first 24 bits — eight each of green, red, blue — and regenerates the rest downstream. The chain is a shift register you can see. One pin, because the pixels do the work.

The generator will not give you a bare strip, and the two extra components are the lesson. A roughly 330 ohm DATA RESISTOR sits between GP16 and the first pixel's DIN: the line carries fast edges into a stub of wire, and the resistor damps ringing and shields the first pixel's input from spikes when supplies come up in the wrong order. And a 100 uF BULK CAPACITOR sits across the strip's power: every pixel switches its LEDs at once, and the capacitor answers the surge locally so the rail does not sag. Your spec names both — data_resistor and decoupling are required fields, and forgetting them earns "U2: ws2812_strip8 requires data_resistor" and "U2: ws2812_strip8 requires decoupling" — and the schematic shows chip, resistor, capacitor: 3 components, 6 traces.

Now the budget, because eight pixels can OUT-EAT the board. Full white, full brightness is roughly $8 \times 60 = 480\,\text{mA}$ — against a 3.3 V rail whose guidance is about 300 mA for everything, radio included. The hardware is not broken; the CONTRACT is that firmware keeps brightness inside the budget, and the bulk capacitor smooths the peaks that remain. This is the third time power has bounded a design in this track — the transistor's load, the servo's stall, the pixels' white — and it will not be the last: current budgets, not pin counts, are what actually limit small boards.