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The LM393 is a simple photo-resistor light sensor that has both analog and digital outputs. The digital output has a trim potentiometer that can be used to set a trigger light level.
In the following example we will use the analog output to measure light level. If you are interested in reading the digital output, please refer to the pulse sensor example sketch.
Wiring Things Up
Start by connecting the radio module.
| Sensor | Arduino | Comment |
|---|---|---|
| GND | GND | Black |
| VCC | VCC (3.3-5V) | Red |
| A0 (analog out) | Analog input 0 (A0) | Green |
Example
/mysensors/MySensors/examples/LightSensor/LightSensor.ino
Last updated by tekka007, 17 Nov 2025, "Update comments (#1574)"
Last updated by tekka007, 17 Nov 2025, "Update comments (#1574)"
/*
* The MySensors Arduino library handles the wireless radio link and protocol
* between your home built sensors/actuators and HA controller of choice.
* The sensors forms a self healing radio network with optional repeaters. Each
* repeater and gateway builds a routing tables in EEPROM which keeps track of the
* network topology allowing messages to be routed to nodes.
*
* Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
* Copyright (C) 2013-2019 Sensnology AB
* Full contributor list: https://github.com/mysensors/MySensors/graphs/contributors
*
* Documentation: http://www.mysensors.org
* Support Forum: http://forum.mysensors.org
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* version 2 as published by the Free Software Foundation.
*
*******************************
*
* REVISION HISTORY
* Version 1.0 - Henrik EKblad
*
* DESCRIPTION
* Example sketch showing how to measure light level using a LM393 photo-resistor
* http://www.mysensors.org/build/light
*/
// Enable debug prints to serial monitor
#define MY_DEBUG
// Enable and select radio type attached
#define MY_RADIO_RF24
//#define MY_RADIO_NRF5_ESB
//#define MY_RADIO_RFM69
//#define MY_RADIO_RFM95
#include <MySensors.h>
#define CHILD_ID_LIGHT 0
#define LIGHT_SENSOR_ANALOG_PIN 0
uint32_t SLEEP_TIME = 30000; // Sleep time between reads (in milliseconds)
MyMessage msg(CHILD_ID_LIGHT, V_LIGHT_LEVEL);
int lastLightLevel;
void presentation()
{
// Send the sketch version information to the gateway and Controller
sendSketchInfo("Light Sensor", "1.0");
// Register all sensors to gateway (they will be created as child devices)
present(CHILD_ID_LIGHT, S_LIGHT_LEVEL);
}
void loop()
{
int16_t lightLevel = (1023-analogRead(LIGHT_SENSOR_ANALOG_PIN))/10.23;
Serial.println(lightLevel);
if (lightLevel != lastLightLevel) {
send(msg.set(lightLevel));
lastLightLevel = lightLevel;
}
sleep(SLEEP_TIME);
}