ESP8266 - Light Sensor Relay

This tutorial instructs you how to use ESP8266 and light sensor to trigger relay. In detail:

By connecting a relay to a light bulb, LED strip, motor, or actuator, we can use an ESP8266 and a light sensor to regulate the light bulb, LED strip, motor, or actuator.

The light sensor is also known as photoresistor, light-dependent resistor, photocell, LDR. The ESP8266 uses a light sensor to measure the ambient light level. If the light is low, the ESP8266 activates the relay, and if it's high, the relay turns off.

Hardware Preparation

1×ESP8266 NodeMCU
1×Micro USB Cable
1×Light Sensor
1×10 kΩ resistor
1×Relay
1×Warning Light Bright Waterproof
1×12V Power Adapter
1×DC Power Jack
1×Breadboard
1×Jumper Wires
1×(Optional) 5V Power Adapter for ESP8266
1×(Optional) ESP8266 Screw Terminal Adapter

Or you can buy the following sensor kit:

1×DIYables Sensor Kit 30 types, 69 units
Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you. We appreciate your support.

Overview of Relay and Light Sensor

If you are not familiar with relay and light sensor (including pinout, functioning, programming ...), the following tutorials can help you:

Wiring Diagram

The wiring diagram between ESP8266 NodeMCU and Light Sensor Relay Light Bulb

This image is created using Fritzing. Click to enlarge image

See more in ESP8266's pinout and how to supply power to the ESP8266 and other components.

ESP8266 Code

/* * This ESP8266 NodeMCU code was developed by newbiely.com * * This ESP8266 NodeMCU code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp8266/esp8266-light-sensor-relay */ #define LIGHT_SENSOR_PIN A0 // The ESP8266 pin connected to light sensor #define RELAY_PIN D8 // The ESP8266 pin connected to Relay #define ANALOG_THRESHOLD 500 void setup() { pinMode(RELAY_PIN, OUTPUT); // Configure the ESP8266 pin to the output mode } void loop() { int analog_value = analogRead(LIGHT_SENSOR_PIN); // read the value on analog pin if (analog_value < ANALOG_THRESHOLD) digitalWrite(RELAY_PIN, HIGH); // turn on Relay else digitalWrite(RELAY_PIN, LOW); // turn off Relay }

Detailed Instructions

To get started with ESP8266 on Arduino IDE, follow these steps:

  • Check out the how to setup environment for ESP8266 on Arduino IDE tutorial if this is your first time using ESP8266.
  • Wire the components as shown in the diagram.
  • Connect the ESP8266 board to your computer using a USB cable.
  • Open Arduino IDE on your computer.
  • Choose the correct ESP8266 board, such as (e.g. NodeMCU 1.0 (ESP-12E Module)), and its respective COM port.
  • Connect an ESP8266 to your computer using a USB cable.
  • Launch the Arduino IDE, select the correct board and port.
  • Copy the code above and open it with the Arduino IDE.
  • Click the Upload button in the Arduino IDE to compile and upload the code to the ESP8266.
Arduino IDE Upload Code
  • Emit light source towards the sensor
  • Check out the relay's state

Code Explanation

Check out the line-by-line explanation contained in the comments of the source code!

Video Tutorial