Control an RGB light from the Blynk app

In this lesson the Blynk app becomes a remote for a colour light. Three sliders mix red, green and blue on the RGB LED module, and a switch starts a rainbow effect that the ESP32 runs by itself. The colour you choose is saved in the Blynk cloud, so the light comes back in the same colour after a power cut.

What you'll learn

• How to handle several app controls at once
• How PWM mixes colours on an RGB LED
• How to run an animation with a timer while staying connected
• How the cloud remembers values with Blynk.syncVirtual()

What you need

• ESP32 board, expansion board and USB cable (ESP32 IoT Starter Kit)
• RGB LED module (45-in-1 Sensor Kit)
• 3 resistors, 220 Ω (ESP32 IoT Starter Kit)
• Breadboard and jumper wires (ESP32 IoT Starter Kit)
• A free Blynk account and the Blynk IoT app on a phone
• A 2.4 GHz Wi-Fi network

Wiring

Sensor modules from different makers can label and order their pins differently. Always follow the labels printed on your module.

Set up Blynk

In the Blynk console, create a new template called RGB light (hardware ESP32, connection type Wi-Fi) and add these datastreams. Lesson 1 shows each step in detail.

Save the template, create a new device from it and copy its three BLYNK_… lines. In the phone app, open the device, tap the wrench icon and add three Sliders (V0, V1, V2) and a Button in switch mode (V3). Link each widget to its datastream.

The sketch

This sketch uses analogWrite(), which needs ESP32 board package version 3.0 or newer (Tools → Board → Boards Manager).

Replace the three BLYNK_… lines at the top with the ones from your device's Device info page, and add your Wi-Fi name and password (2.4 GHz only). The BLYNK_… lines must stay above #include <BlynkSimpleEsp32.h>.

#define BLYNK_TEMPLATE_ID "YOUR_TEMPLATE_ID"
#define BLYNK_TEMPLATE_NAME "RGB light"
#define BLYNK_AUTH_TOKEN "YOUR_AUTH_TOKEN"
#define BLYNK_PRINT Serial          // show connection messages in the Serial Monitor

#include <WiFi.h>
#include <WiFiClient.h>
#include <BlynkSimpleEsp32.h>

char ssid[] = "YOUR_WIFI_NAME";
char pass[] = "YOUR_WIFI_PASSWORD";

const int RED_PIN = 27;
const int GREEN_PIN = 26;
const int BLUE_PIN = 25;

BlynkTimer timer;
int red = 255, green = 80, blue = 0;
bool rainbow = false;
int hue = 0;

void show(int r, int g, int b) {
  analogWrite(RED_PIN, r);
  analogWrite(GREEN_PIN, g);
  analogWrite(BLUE_PIN, b);
}

BLYNK_WRITE(V0) { red = param.asInt();   if (!rainbow) show(red, green, blue); }
BLYNK_WRITE(V1) { green = param.asInt(); if (!rainbow) show(red, green, blue); }
BLYNK_WRITE(V2) { blue = param.asInt();  if (!rainbow) show(red, green, blue); }
BLYNK_WRITE(V3) {
  rainbow = param.asInt();
  if (!rainbow) show(red, green, blue);   // back to your own colour
}

BLYNK_CONNECTED() {
  Blynk.syncVirtual(V0, V1, V2, V3);     // restore the last colour and mode
}

// One small step around the colour wheel (hue 0 ... 359)
void rainbowStep() {
  if (!rainbow) return;
  hue = (hue + 1) % 360;
  int part = hue / 60;
  int rise = (hue % 60) * 255 / 60;     // 0 ... 255 within each sixth
  int fall = 255 - rise;
  switch (part) {
    case 0: show(255, rise, 0); break;  // red to yellow
    case 1: show(fall, 255, 0); break;  // yellow to green
    case 2: show(0, 255, rise); break;  // green to cyan
    case 3: show(0, fall, 255); break;  // cyan to blue
    case 4: show(rise, 0, 255); break;  // blue to magenta
    default: show(255, 0, fall);        // magenta to red
  }
}

void setup() {
  Serial.begin(115200);
  show(red, green, blue);
  Blynk.begin(BLYNK_AUTH_TOKEN, ssid, pass);
  timer.setInterval(30L, rainbowStep);   // about 11 seconds per rainbow
}

void loop() {
  Blynk.run();
  timer.run();
}

How it works

Each slider has its own virtual pin and its own BLYNK_WRITE() function, which saves the new value and updates the LED. PWM switches each colour on and off very fast; analogWrite(pin, 128) keeps it on about half the time, and your eye mixes the three colours into one. The rainbow runs on the ESP32 itself: every 30 ms the timer moves one degree around a colour wheel, fading one colour up or down at a time. Because it runs from a timer, Blynk.run() keeps running between steps, and the switch still responds instantly.

Try this next

• Add a Slider on V4 for the rainbow speed and change the timer interval with timer.changeInterval().
• Replace the three sliders with Blynk's zeRGBa colour picker widget.
• Turn the light on automatically at sunset with the photoresistor module from lesson 1.

Troubleshooting

• The device shows "Offline" in the app: check the Serial Monitor at 115200 baud. "Invalid auth token" means the BLYNK_AUTH_TOKEN line is wrong; if it never connects, check the Wi-Fi name and password, and that your network is 2.4 GHz.
• A colour doesn't light: check that resistor and wire; the module's pin order may differ from the table.
• Red and blue are swapped: swap the pin numbers in the sketch.
• Compile error about analogWrite: update the ESP32 board package to version 3.0 or newer.