🛠 Bandeau NeoPixel piloté par le périphérique RMT

Objectives

Move from a single pixel to an addressable strip by understanding the hardware layer: on the ESP32-S3, the Adafruit NeoPixel library generates WS2812 frames (800 kHz) using the RMT (Remote Control) peripheral, a DMA-driven pulse generator. You will write a "sweep" animation on 8 pixels, size the power supply (a pure white WS2812 draws up to 60 mA), and avoid frame corruption caused by Wi-Fi interrupts.

Hardware

• 1 ESP32-S3 board (GPIO48 free of any onboard pixel, or external strip)
• 1 8-pixel WS2812B strip (5 V)
• 1 330 to 470 ohm resistor for the DATA line
• Dedicated 5 V power supply or USB port capable of providing 500 mA
• Wires: DATA -> GPIO48 via resistor, VCC -> 5 V, GND -> common GND

Complete Code

// Bandeau 8x WS2812 sur GPIO48, trames generees par le peripherique RMT
#include <Adafruit_NeoPixel.h>
#define PIN      48
#define N        8

Adafruit_NeoPixel strip(N, PIN, NEO_GRB + NEO_KHZ800);

uint32_t couleur(uint8_t r, uint8_t g, uint8_t b) {
  return strip.Color(r, g, b);
}

void setup {
  strip.begin;
  strip.setBrightness(60);
  strip.show;                      // eteint tout au demarrage
}

void loop {
  static uint8_t pos = 0;
  static int8_t  dir = 1;
  strip.clear;
  strip.setPixelColor(pos, couleur(255, 80, 0));          // tete
  if (pos > 0)        strip.setPixelColor(pos - 1, couleur(90, 30, 0));
  if (pos < N - 1)    strip.setPixelColor(pos + 1, couleur(90, 30, 0));
  strip.show;
  if (pos == 0) dir = 1; else if (pos == N - 1) dir = -1;
  pos += dir;
  delay(60);
}

Expected Verification

An orange dot sweeps back and forth across the strip with a fading trail. The 8 pixels respond uniformly, without any erratic green pixels. By opening the serial monitor, you can display ESP.getFreeHeap to verify that the internal RAM (512 KB) remains comfortable: the library allocates a copy of the pixel buffer and configures an RMT channel.

Common Errors

• Insufficient power: powering 8 pixels at full white via only the board's 3.3 V pin causes voltage drops and triggers resets; use the strip's 5 V supply and a common ground.
• Forgetting the series resistor on DATA: it often "works," but frames are sensitive to noise on long ribbon cables; the 330-470 ohm resistor is cheap insurance.
• Swapping DATA and the strip's output signal: the input connector is marked with a DATA IN arrow, not DATA OUT.
• Corruption with active Wi-Fi: radio interrupts can shift RMT pulses; the library uses DMA, but in case of flickering, lower the brightness and avoid allocations inside loops.
• Wrong color order: NEO_GRB is the standard wiring for WS2812B; an SK6812 RGBW strip requires NEO_GRB + NEO_KHZ800 with W channel handling.