🛠 Pilote le NeoPixel embarqué (broche D13)

Objectives

Control the status NeoPixel soldered onto the Feather nRF52840 using the Adafruit_NeoPixel library: color, brightness, and a non-blocking "heartbeat" animation. The NeoPixel is powered at 3.3 V, and its data line is connected to the pin exposed by the BSP via PIN_NEOPIXEL; general documentation often refers to it as "D13".

Hardware

• 1× Adafruit Feather nRF52840 Express + micro-USB cable
• Adafruit NeoPixel library (Library Manager)

Full Code

// nrf52840-neopixel-d13.ino
#include <Adafruit_NeoPixel.h>

#define NEO_PIN PIN_NEOPIXEL  // broche NeoPixel embarquee (alias courant D13)
Adafruit_NeoPixel neo(1, NEO_PIN, NEO_GRB + NEO_KHZ800);

uint32_t t0 = 0;

void setup {
  neo.begin;
  neo.setBrightness(40);      // 40/255 : evite d'aveugler et menage la batterie
}

void loop {
  uint32_t t = millis % 1600;              // periode 1,6 s
  float phase = t / 1600.0f * 2.0f * PI;
  uint8_t pulse = (uint8_t)(60 + 195 * pow(sin(phase), 6)); // battement
  neo.setPixelColor(0, neo.Color(pulse, pulse / 6, 0));
  neo.show;
  if (millis - t0 > 20) t0 = millis;     // cadence ~50 fps sans delay
}

Expected Verification

The NeoPixel breathes in warm orange in a continuous loop, without harsh blinking. Barely touching the data pin (with a finger) causes no spurious resets with the code above, as no other WS2812 frame is emitted.

Common Errors

• Confusing the red LED and the NeoPixel: The simple red LED is NOT a NeoPixel; Adafruit pages contradict each other regarding its pin (3 vs 13), so prefer the NeoPixel as recommended by the documentation.
• neo.show inside an interrupt or during BLE: The WS2812 frame requires tight timings that the SoftDevice may disrupt; emit it from loop.
• Brightness at 255 on battery: A NeoPixel at full white draws several tens of mA.
• Inverted color order: NEO_GRB is the correct order for recent embedded NeoPixels; if red/green are inverted, try NEO_RGB.