Homeyduino multi sensor: Co2-LDR-DHT11 [English version]

Homeyduino multi sensor: Co2-LDR-DHT11 [English version]

This time we’ve build a new Multi sensor, a combination between a CO2-, light-, temperature- and humidity sensor that works with Homey and Homey Bridge.

First a short explanation about the importance of good humidity and the dangers of high CO2 levels on your health.

The importance of good humidity

Good humidity has a direct influence on how you feel. For example, too low humidity will cause:

  • Dry skin and throat, burning eyes, chapped lips
  • Headache, fatigue and problems with concentration
  • Shrinking or tearing of wooden furniture and floors

While too high humidity can cause:

  • Increase in bacteria and fungi in yourhome
  • Swelling or rotting of wooden furniture, window frames and floors
  • Overheating within the human body
  • Higher costs of heating: heating moist air costs more energy than heating dry air.

All-in-one Co2 sensor on Amazon.com

DIY Co2 Multi sensor on Amazon or Aliexpress

Amazon you will find the MH-Z19B sensor for around $ 25, combine that with an LDR and a DHT11 sensor , a Wemos D1 for a few dollars and for an amount of $ 40 you have a multi sensor that not only measures , but can also communicate and trigger things in your Smart Home. To make this work, we use Homeyduino , the handy link between Arduino and Homey .

If you prefer to buy on Aliexpress, you can use these links:

Measuring with Homey Insights

In this way you can monitor the course of the humidity and CO2 concentration via Homey Insights, and you can use your DIY sensors as a trigger for your flows. For example, by automatically controlling your mechanical ventilation .

Reading your Co2 - LDR - DHT11 multisensor via Homey Insights


Also necessary, but only to be configured once, a computer or laptop with the following programs installed:

How to connect sensors with Arduino board

Follow the diagram and image below to connect the sensor to the Wemos D1 Mini.

SensorNodeMCU pin
Connection diagramMulti sensor Co2 - LDR - DHT11 on the Wemos D1 Mini, coupled with Homeyduino

CO2 sensor code

Below you will find the code, just like the other Homeyduino projects , uploading is done via Arduino IDE terminal , if you are not familiar with this, read here for an extensive manual . Make sure you have selected the correct board in settings in Arduino IDE and that you upload the code at 9600 baud. The sketch also contains some code to read the measurements via UART. However, we are not using this method in this situation, we only read the sensor via PWM.

// Code for Homeyduino made by Smart Home Blog https://huisvanvandaag.nl. 
// Take a look at my site for more Homeyduino en other Smart Home projects.

#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <Homey.h>
#include <SimpleDHT.h>
#include <SoftwareSerial.h>
#include <MHZ.h>

#define PIN_DHT D4 // DHT11 
SimpleDHT11 dht11; // DHT11

#define CO2_IN D2 // D2 19 // Co2 
#define MH_Z19_RX D6  // Co2
#define MH_Z19_TX D5  // Co2 
MHZ co2(MH_Z19_RX, MH_Z19_TX, CO2_IN, MHZ19B); // Co2

unsigned long previousMillis = 0; // DHT11
const unsigned long interval = 10000; //Interval in milliseconds // DHT11

int LDRsensor = A0; // LDR

void wifi() {
  if (WiFi.status() != WL_CONNECTED) {
    WiFi.begin("<SSID>", "<PASSWORD>"); // Enter WiFi netwerk and password 
    uint8_t timeout = 30;
    while (WiFi.status() != WL_CONNECTED) {
      if (timeout<1) break;
    if (WiFi.status() == WL_CONNECTED) {
      //Print IP address
      Serial.print("Connected to WiFi! (");

void setup() { // DHT11
  Homey.begin("LDR-DHT11-Co2 Multi-sensor");
  Homey.addCapability("measure_humidity"); // DHT11
  Homey.addCapability("measure_temperature");// DHT11
  Homey.addCapability("measure_co2"); // Co2 
  pinMode(CO2_IN, INPUT); // Co2
  Homey.addCapability("measure_luminance"); // LDR

 void  co2loop() { // void voor Co2
  wifi(); // Beide
  Homey.loop(); // Beide
  int ppm_pwm = co2.readCO2PWM();
  Serial.print("PPMpwm: ");
  Homey.setCapabilityValue("measure_co2", (int) ppm_pwm); 


void dhtloop() { // void voor DHT11
  wifi(); // Beide
  Homey.loop(); // Beide
   unsigned long currentMillis = millis(); // DHT11
  if(currentMillis - previousMillis > interval) { // DHT11
    previousMillis = currentMillis; // DHT11
    updateSensor(); // DHT11

void updateSensor() { // DHT11
  byte temperature = 0; // DHT11
  byte humidity = 0; // DHT11
  int err = SimpleDHTErrSuccess; // DHT11
  if ((err = dht11.read(PIN_DHT, &temperature, &humidity, NULL)) != SimpleDHTErrSuccess) { // DHT11
    Serial.print("Read DHT11 failed, err="); Serial.println(err); // DHT11
    return; // DHT11

  Serial.print((int)temperature); Serial.print(" *C, "); // DHT11
  Serial.print((int)humidity); Serial.println(" H"); // DHT11

  Homey.setCapabilityValue("measure_temperature", (int) temperature); // DHT11
  Homey.setCapabilityValue("measure_humidity", (int) humidity); // DHT11

void ldrloop() {
  Serial.print("LDR waarde: ");
  Serial.print(analogRead( LDRsensor));
  Homey.setCapabilityValue("measure_luminance", analogRead( LDRsensor));
  delay(1000); // wacht 1 minuut 60000 ms
void loop(){ // Beide
dhtloop();    //makes two separate voids, one per original code
co2loop();      //akes two separate voids, one per original code
ldrloop();      //akes two separate voids, one per original code


Now that you have successfully uploaded the code, we will test it to make sure it works. youdo this by opening the Serial Monitor in Arduino IDE, click on Tools and then Serial Monitor or use the keyboard shortcut CTRL+SHIFT+M.

You can read the Multi sensor CO2, ldr, temperature and humidity via the serial monitor.


Using these sensors and code you can build a well-functioning Multi sensor for a fraction of the normal costs, while having the possibilities to connect it to your Smart Home. Normally you would probably pay several hundred dollars for a similar sensor, while it only comes with a fraction of the options.

Link with mechanical ventilation

It is especially nice when you use this sensor in combination with mechanical ventilation, such as the system below from Itho Daalderop. This can also be linked to Homey via the Spider app .

When the CO2 concentration indoors gets too high, it can automatically start your mechanical ventilation via a ‘flow’. In this way you always have a healthy climate indoors.

Homeyduino Co2 flow in Homey
Homey Co2 flow that automatically starts when the Co2 concentration is too high
Spider thermostat and Gateway from Itho Daalderop, with which you can easily connect the mechanical ventilation with Homey

Spider thermostat and Gateway from Itho Daalderop , with which you can easily connect the mechanical ventilation with Homey

Mechanical ventilation from Itho Daalderop, easy to link with Homey for a healthier indoor climate.

More projects coming soon! Sign up here so you don’t have to miss anything!

Mike | Huisvanvandaag

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