MQ135 is a Gas sensor. It works on analogue and digital pins with Arduino boards. It gives analogue value in PPM of Air Quality. When we use a digital pin, it gives on signal at a particular value of analogue. This can be adjusted via potentiometer. So, you can also detect a particular gas without using any microcontroller. Just seeing a green LED, you can know it.
Nowadays, we see different gasses being emitted in atmospheres from home appliances like air conditioner and industrial chimneys. Monitoring of these gasses is very important as a safety point of view.
Here, for this project I will use Wemos D1 Board which is a ESP8266 based IoT board.
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What is MQ135 Gas Sensor?
The MQ-135 gas sensor module consists of a steel exoskeleton under which a sensing element is housed. This sensing element is subjected to the current through connecting leads. So, this current is known as the heating current through it, the gases coming close to the sensing element get ionized and are absorbed by the sensing element. This changes the resistance of the sensing element which alters the value of the current going out of it. This resistance value shows in analogue reading.
It works on the 5V pin of Arduino or ESP8266 boards. It is suitable for detecting NH3, NOx, alcohol, Benzene, smoke, CO2, etc.
Connect ESP8266 with 1602 LCD via I2C
This display works with 5V power and via the I2C interface. To know in detail, how to connect LCD display via I2C, Follow this post.
So, now connect display according to the diagram below.
So, here I have connected 5V of ESP8266 with VCC of MQ135. I will not use Digital Pin.
Firstly, in the void setup area, I have initialized display with static texts like PPM, Air quality.
Next, in the void loop area, we are displaying sensor value in every 2 seconds which is being read on line no 21.
Arduino Sketch for MQ135 Gas Sensor
MQ135 with 1602 LCD using I2C
LiquidCrystal_I2C lcd(0x27,16,2); // set the LCD address to 0x27 for a 16 chars and 2 line display
int sensorValue = analogRead(A0);
Finally, here you can see Air quality is showing in PPM on the LCD display.
Watch Video Tutorial
If you do not have LCD display, you can also do this using ST7789 SPI TFT LCD Display. Follow this post.