Blink the RGB LED

Why the usual blink sketch does nothing

Copy an ESP32 blink example onto this board and nothing happens. The example does digitalWrite(LED_BUILTIN, HIGH), and on this board GPIO 48 is not wired to a plain LED. It is wired to a WS2812: a tiny controller with an RGB LED attached, which listens for a message.

Holding a pin high is not a message. So the sketch runs perfectly and the LED stays dark, and people conclude the board is faulty on their first evening.

One wire, twenty-four bits

The WS2812 takes three bytes — one per colour — clocked in on a single pin with timing measured in hundreds of nanoseconds. Green goes first.

That green-first order is the whole reason the third parameter of addLeds is GRB. Set it to RGB and the LED still takes the first byte it receives as green, so red and green swap — while white, which is all three at full, keeps looking exactly right. The mistake passes the test people run to check for it.

Brightness is not a fourth byte. setBrightness scales the three values before they are sent, so 40 out of 255 is not a dimmer switch — it is just smaller numbers going down the same wire.

Install FastLED

Sketch ▸ Include Library ▸ Manage Libraries, search FastLED, and install the one by Daniel Garcia.

It is the library that knows the timing, and on an ESP32 it drives the pin from the RMT peripheral rather than from your loop — which is why the colours stay steady when the rest of your sketch gets busy.

Adafruit_NeoPixel does the same job with different spelling. Either is fine; the samples here use FastLED.

What you should see

Upload, and the LED runs red, off, green, off, blue, off, forever. If it does, the whole chain works: the IDE, the package, the port, the upload and the board.

Two things worth doing before you move on:

• Change BRIGHTNESS to 255 and upload again. It is unpleasantly bright, and the point is that you now know what the top of the range feels like.
• Change GRB to RGB and upload again, so you have seen the swap once, deliberately. The next time somebody's "faulty" LED shows the wrong colour you will know where to look in ten seconds.

/*  Lonely Binary ESP32-S3 N16R8 — the on-board RGB LED
    Tools ▸ Board ESP32S3 Dev Module · USB CDC On Boot Enabled
    Library: FastLED by Daniel Garcia                        */

#include <FastLED.h>

#define LED_PIN     48        // printed on the board as RGB@IO48
#define NUM_LEDS    1
#define BRIGHTNESS  40        // 0–255; 255 is uncomfortable to look at

CRGB leds[NUM_LEDS];

void setup() {
  FastLED.addLeds<WS2812, LED_PIN, GRB>(leds, NUM_LEDS);
  FastLED.setBrightness(BRIGHTNESS);
  FastLED.clear();
  FastLED.show();
}

void flash(CRGB colour) {
  leds[0] = colour;
  FastLED.show();
  delay(1000);
  leds[0] = CRGB::Black;
  FastLED.show();
  delay(400);
}

void loop() {
  flash(CRGB::Red);
  flash(CRGB::Green);
  flash(CRGB::Blue);
}