Measuring CO2 Concentration in Air using Arduino and MQ-135 Sensor

This project creates an air quality monitoring system using an Arduino Nano as the central processing unit. The core sensing element is the MQ-135 sensor module, which is designed to detect gases such as carbon dioxide in the surrounding air. Inside the MQ-135, a small heating element warms up a chemical sensor layer. When gas molecules interact with this heated layer, the electrical resistance of the sensor changes. This variation produces an analog voltage output that corresponds to the concentration of the gas in the ppm range. The Arduino Nano reads this analog signal through one of its built-in analog-to-digital converter pins, utilizing a 22KΩ resistor as part of the voltage configuration circuit. Once the Arduino processes the incoming analog data, it formats the readings and sends them to a 0.96-inch SPI OLED display module powered by the SSD1306 controller. The display visually presents the real-time CO2 concentration data to the user using graphics and text managed by the Adafruit GFX, SSD1306, and SPI libraries, while the MQ135 library helps translate the raw sensor values into readable air quality metrics.