Four-Lead RGB LED: Common Terminal and ESP32 Color Test

Before you start

Board and software

Classic ESP32-WROOM-32/32E DevKit with the specified unused GPIOs exposed; Arduino IDE 2.x and Arduino-ESP32 3.x. Other families require their own pin map. Serial Monitor: 115200 baud. No extra library.

Supported hardware

A documented bare four-lead common-cathode RGB LED whose channels tolerate the resistor-limited 3.3 V test. Confirm actual R/G/B/common leads before wiring. The illustration cannot establish common-terminal type or package size.

Prerequisites and parts

IDE setup, Blink, RGB LED and three known 470 ohm / 0.25 W resistors; breadboard, wires and part documentation.

Expected result

Red, green and blue channels are requested in turn for one second, with an all-off pause. Blue/green brightness at 3.3 V is not guaranteed; it depends on actual forward voltage.

Verification limits

Documentation and automated content/browser checks only in this update. No ESP32 compilation or physical hardware testing. The approved image depicts a component family; it does not authenticate a model, rating or terminal order.

Overview

02Technical Specifications

Arduino library: Arduino-ESP32 3.x; no additional library

03Pinout

• Common cathode Verified by the real part datasheet; no physical lead order assumed. ESP32 GND Verified by the real part datasheet; no physical lead order assumed.
• Red anode One resistor for this channel. GPIO25 through 470 ohms One resistor for this channel.
• Green anode One resistor for this channel. GPIO26 through 470 ohms One resistor for this channel.
• Blue anode One resistor for this channel. GPIO27 through 470 ohms One resistor for this channel.

04Wiring Diagram

Verified common cathode → GND; R/G/B anodes → separate 470 ohm resistors → GPIO25/26/27.

Open wiring diagram at full size (new tab)

1. 1

   Power off and identify common-terminal type and all four leads.

2. 2

   Wire one resistor in each color path; connect common cathode to GND.

3. 3

   Upload, then compare Serial channel labels with the actual emitted colors.

Wiring and matching Arduino code

One color at a time

Verified common cathode → GND; R/G/B anodes → separate 470 ohm resistors → GPIO25/26/27.

#include <Arduino.h>
constexpr uint8_t RED_PIN = 25, GREEN_PIN = 26, BLUE_PIN = 27;
const uint8_t pins[] = {RED_PIN, GREEN_PIN, BLUE_PIN};
const char* names[] = {"RED", "GREEN", "BLUE"};
void allOff() { for (uint8_t pin : pins) digitalWrite(pin, LOW); }
void setup() {
  Serial.begin(115200);
  for (uint8_t pin : pins) { pinMode(pin, OUTPUT); digitalWrite(pin, LOW); }
}
void loop() {
  for (uint8_t i = 0; i < 3; ++i) {
    allOff();
    digitalWrite(pins[i], HIGH);
    Serial.println(names[i]);
    delay(1000);
    allOff();
    delay(300);
  }
}

Common-cathode only. Begin with one active color to identify leads; this is not calibrated color mixing or a brightness measurement.

How it works

Technical references

• Espressif GPIO API — Pin modes and digital output on Arduino-ESP32.
• Kingbright RGB LED datasheet — Example electrical characteristics and package circuit; not identification of the generic illustration.