ESP32 - Light Sensor Triggers Relay

This tutorial instructs you how to use ESP32, light sensor and relay to do a project that:

We can extend this tutorial to automatically turn on a led strip or light bulb when it is dark.

Hardware Used In This Tutorial

1×ESP-WROOM-32 Dev Module
1×Micro USB Cable
1×Light Sensor
1×10 kΩ resistor
1×Relay
1×Warning Light Bright Waterproof
1×12V Power Adapter
1×Breadboard
n×Jumper Wires
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Introduction to Relay and Light Sensor

We have specific tutorials about relay and light sensor. Each tutorial contains detailed information and step-by-step instructions about hardware pinout, working principle, wiring connection to ESP32, ESP32 code... Learn more about them at the following links:

Wiring Diagram

wiring diagram between esp32 light sensor relay light bulb

This image is created using Fritzing. Click to enlarge image

ESP32 Code

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-light-sensor-triggers-relay */ #define LIGHT_SENSOR_PIN 4 // ESP32 pin GIOP4 (ADC10) connected to light sensor #define RELAY_PIN 27 // ESP32 pin GIOP27 connected to Relay #define ANALOG_THRESHOLD 500 void setup() { pinMode(RELAY_PIN, OUTPUT); // set ESP32 pin to output mode } void loop() { int analogValue = analogRead(LIGHT_SENSOR_PIN); // read the value on analog pin if (analogValue < ANALOG_THRESHOLD) digitalWrite(RELAY_PIN, HIGH); // turn on Relay else digitalWrite(RELAY_PIN, LOW); // turn off Relay }

Quick Instructions

  • If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
  • Do the wiring as above image.
  • Connect the ESP32 board to your PC via a micro USB cable
  • Open Arduino IDE on your PC.
  • Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
  • Copy the above code and paste it to Arduino IDE.
  • Compile and upload code to ESP32 board by clicking Upload button on Arduino IDE
  • Arduino IDE Upload Code
  • Radiates light to sensor
  • See the change of relay's state

Line-by-line Code Explanation

The above ESP32 code contains line-by-line explanation. Please read the comments in the code!

Video Tutorial

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