Introduction
Monitoring air quality and detecting harmful gases is critical for health and safety in homes, industries, and public spaces. Gas sensors provide a simple way to measure the concentration of gases in the environment, which can be used to detect dangerous gases like carbon monoxide, and methane, or even to monitor indoor air quality. In this lesson, we will explore how to use gas sensors with Arduino, focusing on wiring, coding, and the basics of gas detection.
What is a Gas Sensor?
A gas sensor is an electronic device that detects the presence or concentration of gases in the air. These sensors typically detect gases such as carbon monoxide, methane, propane, and alcohol vapors. Based on the gas concentration, they change their electrical properties, such as resistance, allowing them to output a measurable signal that can be read by a microcontroller like Arduino.
Types of Gas Sensors
MQ Series Sensors
The MQ series of gas sensors are widely used due to their affordability and versatility. Each sensor in the MQ family is specialized for detecting certain types of gases. For instance:
- MQ-2: Detects flammable gases like methane, propane, hydrogen, and smoke.
- MQ-3: Specifically used for alcohol detection, often in breathalyzers.
- MQ-4: Suitable for detecting methane (CH₄) and natural gas.
- MQ-5: Detects LPG (Liquefied Petroleum Gas), methane, and hydrogen.
- MQ-6: Sensitive to LPG and is ideal for gas leak detection.
- MQ-7: Designed for detecting carbon monoxide (CO), crucial for monitoring indoor air quality.
- MQ-9: Detects both carbon monoxide (CO) and combustible gases.
The MQ sensors offer a cost-effective solution for projects involving gas monitoring, providing analog outputs that are easy to read with microcontrollers like Arduino.
CCS811 Sensor
The CCS811 is a more advanced air quality sensor that measures carbon dioxide (CO₂) levels and volatile organic compounds (VOCs) in the air. Unlike the MQ series, it uses a digital interface and provides more accurate readings, especially for indoor air quality monitoring.
How Gas Sensors Work
Basic Principle of Gas Detection
Gas sensors work by changing their electrical resistance in response to the concentration of specific gases in the environment. The MQ series sensors use a metal oxide semiconductor layer that reacts with the gas molecules, causing the sensor’s resistance to vary depending on the concentration of the gas. This resistance change is converted into an electrical signal that can be measured by the Arduino.
Internal Structure of MQ Sensors
MQ sensors have a heating element and a sensing layer. The heating element raises the temperature of the sensing layer to a high level, which allows it to react with gas molecules in the air. When gas molecules contact the sensing layer, they change their resistance. The microcontroller then measures this change and converts it into a readable value.
Connecting an MQ sensor to an Arduino
Wiring Diagram
Most MQ sensors have three main pins: VCC, GND, and A0 (analog output). Here’s how to wire it:
- VCC: Connect to the 5V pin on the Arduino.
- GND: Connect to one of the Arduino’s GND pins.
- A0 (analog output): Connect to one of the Arduino’s analog input pins (e.g., A0).
Arduino Code
Here is an example of how to read gas concentration values using an MQ-3 sensor and display them on the Arduino serial monitor.
int sensorPin = A0; // Analog pin connected to A0 on the sensor
void setup() {
Serial.begin(9600); // Start serial communication at 9600 baud
}
void loop() {
int sensorValue = analogRead(sensorPin); // Read the analog sensor value
Serial.print("Gas Concentration: ");
Serial.println(sensorValue); // Print the sensor value
delay(1000); // Wait 1 second before the next reading
}
Explanation of the Code:
- analogRead(): This function reads the voltage from the sensor’s analog output pin and converts it into a digital value (ranging from 0 to 1023).
- The gas concentration value is printed to the serial monitor, providing real-time feedback on the levels of gas detected by the sensor.
Conclusion
Gas sensors, particularly the MQ series, offer a simple and cost-effective way to monitor air quality and detect harmful gases. By understanding how these sensors work, wiring them correctly, and writing basic code, you can easily integrate gas detection into their Arduino projects.