Arduino Air Quality Monitoring System

Situatie

Build your own Arduino-based Air Quality Monitor using sensors like the MQ-135, MQ-7, and DHT11/DHT22. This guide explains how the sensors work, how to wire them, and includes a fully commented Arduino code example.

Components Needed

Component	Qty	Description
Arduino Uno / Nano / Mega	1	Main microcontroller
MQ-135 Gas Sensor	1	Detects VOCs, NH₃, CO₂, smoke, pollution
DHT11 or DHT22	1	Temperature & Humidity
MQ-7 (optional)	1	Carbon Monoxide sensor
0.96″ OLED (optional)	1	Displays readings
Breadboard & Jumper Wires	–	Wiring
USB Cable	1	Power + programming

How the Sensors Work

MQ-135 (Air Quality Sensor)

Detects harmful gases such as CO₂, NH₃, NOx, benzene, and VOCs. The analog output value increases when the air becomes more polluted. Requires a short preheat time for accuracy.

MQ-7 (Carbon Monoxide)

Detects CO gas. Optional component for advanced monitoring.

DHT11 / DHT22

Reads temperature and humidity. These values help interpret gas sensor readings more accurately.

MQ-135 Wiring

MQ135 → Arduino
VCC   → 5V
GND   → GND
A0    → A0

DHT11 / DHT22

DHT Sensor → Arduino
VCC        → 5V
GND        → GND
DATA       → D2

OLED (I2C)

OLED → Arduino
VCC  → 5V
GND  → GND
SDA  → A4
SCL  → A5

Arduino Code (Copy & Paste)

#include <DHT.h>


#define DHTPIN 2

#define DHTTYPE DHT22   // change to DHT11 if needed

DHT dht(DHTPIN, DHTTYPE);
int mq135Pin = A0;
void setup() {

  Serial.begin(9600);

  dht.begin();

}
void loop() {
  // --- Read MQ135 Sensor ---

  int mqValue = analogRead(mq135Pin);

  float airQuality = map(mqValue, 0, 1023, 0, 500);

  // 0 = clean air, 500 = very polluted
  // --- Read Temperature & Humidity ---

  float humidity = dht.readHumidity();

  float temperature = dht.readTemperature();
  // --- Output Data ---

  Serial.println("----------- AIR QUALITY MONITOR -----------");

  Serial.print("MQ135 Raw Value: ");

  Serial.println(mqValue);
  Serial.print("Air Quality Index (approx): ");

  Serial.print(airQuality);

  Serial.println(" / 500");
  Serial.print("Temperature: ");

  Serial.print(temperature);

  Serial.println(" *C");
  Serial.print("Humidity: ");

  Serial.print(humidity);

  Serial.println(" %");
  Serial.println("-------------------------------------------\\n");

delay(1000); }

Understanding the Readings

MQ135 Reading	Air Quality	Description
0–80	Excellent	Very clean air
80–150	Good	Normal indoor air
150–250	Moderate	Needs ventilation
250–350	Poor	Polluted environment
350–500+	Hazardous	High VOCs or smoke detected

Troubleshooting

Sensor always reads high: MQ-135 needs 1–5 minutes warm-up time.
No DHT readings: Check DATA pin and DHT type in code.
Unstable values: Add a 100nF decoupling capacitor to MQ sensor.
OLED not showing: Wrong I2C address — run an I2C scanner.

Solutie

Tip solutie

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