This blog assumes that you already have the required materials discussed in Blog #2: Gathering the Essentials: Materials for Your Classroom Indoor Air Quality Monitoring Project. Below are the steps for testing the individual components together with the SAMD21 Microcontroller and Arduino IDE.

I. Grove - Temperature & Humidity Sensor (DHT20)

• Prepare your Grove Temperature and Humidity DHT20 Sensor.
• Connect your Grove Temperature and Humidity DHT20 Sensor to the SAMD21 Microcontroller pins. We have four pins that need to be connected; 5V, GND, SDA, and SCL.
• Connect your Seeeduino XIAO SAMD21 Microcontroller to your PC or Laptop via a USB Type-C Cable.
• Download the Seeed DHT library from Github.
• Refer to "How to install library to install library" for Arduino.
• Open the “DHTtester” example via the path: File --> Examples --> Grove_Humidity_Temperature_Sensor-master --> DHTtester. Through this demo, we can read the temperature and relative humidity information of the environment.
• Upload the demo. If you do not know how to upload the code, please check how to upload the code.
• Open the Serial Monitor of Arduino IDE by clicking Tool-> Serial Monitor. Or tap the CTRL+SHIFT+M keyboard keys at the same time. if everything goes well, you will get the temperature and humidity readings.

II. RGB LED

• Prepare your RGB LED Sensor.
• Connect your RGB LED to the SAMD21 Microcontroller pins. We have four pins that need to be connected; GND, R, G, and B. In my case, the R, G, and B pins are digital pins which are connected to 10, 9, and 8 digital pins of SAMD21 MCU.
• Connect your Seeeduino XIAO SAMD21 Microcontroller to your PC or Laptop via a USB Type-C Cable.
• Download the Seeed DHT library from Github.
• Refer to "How to install library to install library" for Arduino.
• Open the “ Flash” example via the path: File --> Examples --> RGB --> Flash. Through this demo, we can make our RGB flash like a regular LED flasher circuit.
• Upload the demo. If you do not know how to upload the code, please check how to upload the code.

III. Buzzer

• Prepare your Buzzer Sensor.
• Connect your Buzzer to the SAMD21 Microcontroller pins. We have three pins that need to be connected; GND, 5V, and OUT. In my case, the OUT pin is a digital pin which is connected to digital pin 3 of SAMD21 MCU.
• Connect your Seeeduino XIAO SAMD21 Microcontroller to your PC or Laptop via a USB Type-C Cable.
• Open the “ Blink” example via the path: File --> Examples --> Basics--> Blink. Through this demo, we can make our Buzzer on and off like every second.
• Upload the demo. If you do not know how to upload the code, please check how to upload the code.

IV. MQ135 Gas Sensor

• Prepare your MQ135 Gas Sensor.
• Connect your MQ135 Gas Sensor to the SAMD21 Microcontroller pins. We have three pins that need to be connected; GND, 5V, and OUT. In my case, the OUT pin is an analog pin which is connected to analog pin A1 of SAMD21 MCU.
• Connect your Seeeduino XIAO SAMD21 Microcontroller to your PC or Laptop via a USB Type-C Cable.
• Download the MQ135 library from Github.
• Refer to "How to install library to install library" for Arduino.
• Open the “MQ135” example via the path: File --> Examples --> MQ135 --> MQ135. Through this demo, we can read the carbon dioxide information of the environment.
• Upload the demo. If you do not know how to upload the code, please check how to upload the code.
• Open the Serial Monitor of Arduino IDE by clicking Tool-> Serial Monitor. Or tap the CTRL+SHIFT+M keyboard keys at the same time. If everything goes well, you will get the carbon dioxide readings.