ESP32 - Light Sensor Triggers Relay

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

Turns relay on if the analog value measured from light sensor's is below a threshold,
Turns relay off if the analog value measured from light sensor's is above a threshold,

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	×	(Optional) Solenoid Lock
1	×	(Optional) 12V Active Buzzer
1	×	(Optional) 12V Cooling Fan
1	×	(Optional) 12V Warning Light Bright Waterproof
1	×	12V Power Adapter
1	×	Breadboard
1	×	Jumper Wires
1	×	(Optional) DC Power Jack
1	×	(Optional) ESP32 Screw Terminal Adapter

Or you can buy the following sensor kit:

DIYables Sensor Kit 30 types, 69 units

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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

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 36 // ESP32 pin GPIO36 (ADC0) connected to light sensor #define RELAY_PIN 27 // ESP32 pin GPIO27 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

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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