Embarking on an indoor air quality (IAQ) monitoring project to keep carbon dioxide (CO2) levels in check in your classroom is commendable. Properly equipping yourself with the right materials is the first step to ensure your project's success. This blog will guide you through the essential materials required for an effective IAQ monitoring project in your classroom.
1. CO2 Sensors: The Heart of Your Project
The most critical component of your project is the CO2 sensor. This sensor is responsible for accurately measuring the CO2 levels in your classroom. These sensors come in various types, including non-dispersive infrared (NDIR) sensors and metal-oxide semiconductor (MOS) sensors. NDIR sensors are commonly used for IAQ monitoring, offering high precision and reliability. Ensure that the sensor you select is compatible with your monitoring system and provides accurate readings. The only available CO2 sensor at my disposition is the MQ-135 Gas Sensor, which is a MOS sensor.
The MQ135 air quality sensor specifications and features are listed below.
- It has a wide detection scope.
- High sensitivity and faster response.
- Long life and stability.
- The operating voltage: +5V.
- Measures and detects NH3, alcohol, NOx, Benzene, CO2, smoke etc.
- Range of analog output voltage: 0V-5V.
- Range of digital output voltage: 0V-5V (TTL logic).
- Duration of preheating: 20 seconds.
- Used as an analog or digital sensor.
- The potentiometer is used to vary the sensitivity of the digital pin.
- Heating Voltage: 5V±0.1.
- Load resistance is adjustable.
- Heater resistance: 33ohms±5%.
- Heating consumption:<800mW.
- Operating temperature: -10°C to -45°C.
- Storage temperature: -20°C to -70°C.
- Related humidity: <95%Rh.
- Oxygen concentration: 21% (affects the sensitivity).
- Sensing resistance: 30kiloohms to 200kiloohms.
- Concentration slope rate: ≤0.65.
- Preheat time: over 24 hrs.
- Simple drive circuit.
2. Microcontroller - Seeed Studio XIAO SAMD21
The Seeed Studio XIAO SAMD21 is the smallest member of the Seeeduino family. It carries the powerful ATSAMD21G18A-MU which is a low-power microcontrollers. On the other hand, this little board has good performance in processing but needs less power. As a matter of fact, it is designed in a tiny size and can be used for wearable devices and small projects.
Seeed Studio XIAO SAMD21 has 14 PINs, which can be used for 11 digital interfaces, 11 mock interfaces, 10 PWM interfaces (d1-d10), 1 DAC output pin D0, 1 SWD pad interface, 1 I2C interface, 1 SPI interface, 1 UART interface, Serial communication indicator (T/R), Blink light (L) through pin multiplexing. The colors of LEDs(Power,L,RX,TX) are green, yellow, blue and blue. Moreover, Seeed Studio XIAO SAMD21 has a Type-C interface which can supply power and download code. There are two reset button, you can short connect them to reset the board.
4. Temperature and Humidity Sensor - Grove Temperature&Humidity Sensor (DHT20)
A temperature and humidity sensor, often referred to as a hygrometer or a combined temperature and humidity sensor, is a device designed to measure and monitor both temperature and relative humidity in the surrounding environment. These sensors are commonly used in various applications, including weather monitoring, climate control systems, industrial processes, and even consumer products. In my case, I utilized the Grove - Temperature&Humidity Sensor(DHT20) that was sent to be altogether with SeeedStudio Xiao SAMD21 MCU.
Here's a brief explanation of each component:
Temperature Sensor: This part of the sensor measures the temperature of the environment and provides a numerical value in degrees Celsius (°C) or Fahrenheit (°F). Common types of temperature sensors used in these devices include thermistors, resistance temperature detectors (RTDs), or integrated circuits that can accurately measure temperature.
Humidity Sensor: The humidity sensor measures the relative humidity (RH) in the air, which is a measure of the amount of moisture or water vapor in the air as a percentage. Common types of humidity sensors include capacitive humidity sensors, resistive humidity sensors, and more advanced devices using integrated circuits.
4. Power Supply
A stable power supply is crucial to keep your monitoring system running. Depending on your project's requirements, you may use rechargeable batteries, a power adapter, or a combination of both to ensure uninterrupted operation. In my case, I used a 5V power supply which utilizes the USB Type-C cable.
5. Display and Notification Unit
While not strictly necessary, a display unit can provide real-time CO2 level information in the classroom. This could be a simple LED display or a more advanced graphical user interface on a screen.In my case, I used a RGB LED and 20x4 I2C LCD display for visuals. For notification, I utilized a buzzer.
6. Assorted Jumper Wires
Jumper wires are electrical wires used in electronics and electrical projects to establish connections between various components on a breadboard, PCB (Printed Circuit Board), or other electronic prototyping platforms. They are an essential tool for building, testing, and debugging electronic circuits.
7. Software Applications.
We need a software application for us to be able to program our hardware materials. In my case, I used Arduino IDE 1.8.19 since the SeeedStudio Xiao SAMD21.