ESP8266-AirSensor

Using a ESP8266 to collect and analyze data about the air (temperature, humidity, etc.)

This project is about building an IoT device that collects information about the air. The sensor data should then be sent to Thingspeak or an MQTT broker. Data on temperature, humidity and air quality in your room can be viewed online and on an LCD display. In addition, I would like to integrate a small web server that provides the sensor data via a REST API. In the future I might want set up a notification system that will send you a notification when there is bad air in your room.

Finished soldered board	LCD Display

DHT11-Thingspeak

This sketch sends temperature and humidity data from the DHT11 sensor to Thingspeak.

Hardware Requirements

• NodeMCU ESP8266 Board
• 4.7k Ohm Resistor
• DHT11 Sensor

Wiring

Circuit Diagram	Breadboard Wiring

DHT11 Pins	ESP8266 Pins
GND	G
VCC	3V
Signal	RX (GPIO3)

DHT11-MQ135-Thingspeak

This sketch sends data from DHT11 and MQ135 to Thingspeak.

Hardware Requirements

• NodeMCU ESP8266 Board
• 4.7k Ohm Resistor
• DHT11 Sensor
• MQ135 Sensor

Software Libraries

MQ135 by GeorgK: https://github.com/GeorgK/MQ135

Wiring

Circuit Diagram	Breadboard Wiring

DHT11 Pins	ESP8266 Pins	MQ135 Pins
GND	G	GND
VCC	3V
Signal	RX (GPIO3)
	A0	A0
	VU (5V)	VCC

Setup

1. At first, the sensor has to be calibrated. For this, connect the sensor to the circuit and leave it powered on for 24 hours to burn in.
2. Then put it into outside air for one hour at preferably at 20°C and 35% relative humidity. After that the calibration value should have settled. Now we have to read out the calibration value: rzero = gasSensor.getRZero();
3. After that we replace the predefined RZero constant with our determined value in the file MQ135.h from the MQ135 sensor library: #define RZERO 890 (Note: Every sensor has a own specific RZero!)

DHT11-MQ135-Thingspeak-Web

This sketch is a refactored version of the previous sketch DHT11-MQ135-Thingspeak. Additionally a webserver was included which provides the sensor data in JSON format.

JSON Output

URL	Example result
http://<IP-Address>/	{"temperature":23.60, "humidity":31.00, "ppm":443.96, "rzero":979.75}
http://<IP-Address>/dht11	{"temperature":23.60, "humidity":31.00}
http://<IP-Address>/mq135	{"ppm":443.96, "rzero":979.75}

DHT11-MQ135-Thingspeak-Web-Display

In order to add a display to this setup, we extend the previous installation DHT11-MQ135-Thingspeak-Web. The source code can be found in DHT11-MQ135-Thingspeak-Web-Display.ino using address 0x27 for the display. Then you get information such as air humidity, temperature and airpm (particles per million) on your screen.

Hardware Requirements

• NodeMCU ESP8266 Board
• 4.7k Ohm Resistor
• DHT11 Sensor
• MQ135 Sensor
• 16x2 LCD Display
• I2C LCD Interface Adapter

Wiring

We do the same wiring like above plus some additional connections between the LCD-Display and the ESP8266 board.

Display Pins	ESP8266 Pins
SCL	D1
SDA	D2
VCC	VU
GND	G