Gas Sensors - MQ Series, MG811, CO, NO2, H2S Detection – Robocraze

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Gas detection sensors detect the presence and concentration of hazardous gases and vapors such as toxic or explosive gases, volatile organic compounds (VOCs), humidity, and odors.

MQ series gas sensors are a type of electrochemical gas detector that can detect the presence of a variety of gases, including combustible gases like methane and propane, and toxic gases like carbon monoxide. These gas monitor sensors are relatively small, low-cost, and easy to use, and they can operate in a variety of different environments.

Gas Sensors for Air Quality Monitoring, Safety & IoT Projects

Explore gas sensors for air quality monitoring, gas leak detection, industrial safety and IoT projects. This collection includes popular MQ series gas sensors, MG811 CO₂ sensors, and Fermion digital gas sensors that work with Arduino, Raspberry Pi, ESP32 and other microcontrollers.

Gas Sensor Categories

MQ Series Gas Sensors – Widely used analog gas sensors (MQ-2, MQ-3, MQ-4, MQ-7, MQ-135, etc.) for detecting LPG, smoke, methane, alcohol, CO, CO₂, and overall air quality.
MG811 CO₂ Sensor – Dedicated CO₂ gas sensor suitable for indoor air quality, ventilation systems, greenhouses and environmental monitoring.
Fermion Gas Sensors – Digital and analog gas sensor modules with built-in signal conditioning or I²C interfaces for easy integration in IoT and data-logging projects.

Applications

Indoor air quality monitoring (CO₂, VOCs, smoke, LPG, etc.)
Gas leak detection in kitchens, factories and workshops
IoT-based safety systems and smart alarms
Greenhouse and environmental monitoring
Smart home ventilation and HVAC control
Educational and DIY projects with Arduino and Raspberry Pi

Connection & Wiring Guides

Use these wiring references as a starting point when connecting gas sensors to your microcontroller:

MQ Series Gas Sensor Module to Arduino (Analog Output)

MQ Module Pin   →   Arduino
-----------------------------
VCC             →   5V
GND             →   GND
AO (Analog)     →   A0
DO (Digital)*   →   D2 (optional)

*DO can be used with the onboard comparator + potentiometer for simple threshold-based alarms.

MG811 CO₂ Sensor Module to Arduino

MG811 Module Pin   →   Arduino
--------------------------------
VCC                →   6V–12V (as per module spec)
GND                →   GND
AO (Analog)        →   A1
DO (Digital)*      →   D3 (optional alarm output)

Note: Many MG811 modules have onboard amplifiers and require preheating time for stable readings.

Fermion I²C Gas Sensor to Arduino

Fermion I²C Pin   →   Arduino
-------------------------------
VCC               →   3.3V or 5V (check module)
GND               →   GND
SDA               →   A4 (on Arduino UNO)
SCL               →   A5 (on Arduino UNO)

For other boards, connect SDA/SCL to their respective I²C pins.

Fermion / MQ (via ADC) to Raspberry Pi

For analog sensors (MQ series, MG811) with Raspberry Pi, use an ADC such as MCP3008:

MQ AO     → MCP3008 CH0
MCP3008 VDD/VREF → 3.3V
MCP3008 AGND/DGND → GND
MCP3008 CLK  → Raspberry Pi SCLK
MCP3008 DOUT → Raspberry Pi MISO
MCP3008 DIN  → Raspberry Pi MOSI
MCP3008 CS   → Raspberry Pi CE0

Arduino Example Code – Read MQ Gas Sensor


// Simple MQ gas sensor reading with Arduino
const int mqPin = A0;
int sensorValue = 0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  sensorValue = analogRead(mqPin);
  float voltage = sensorValue * (5.0 / 1023.0);

  Serial.print("Raw value: ");
  Serial.print(sensorValue);
  Serial.print("  | Voltage: ");
  Serial.println(voltage);

  // Simple threshold example (tune after calibration)
  if (sensorValue > 400) {
    Serial.println("Gas concentration high! (Above threshold)");
  }

  delay(1000);
}

Raspberry Pi Example Code – Read MQ via MCP3008 (Python)


import time
import spidev

spi = spidev.SpiDev()
spi.open(0, 0)           # bus 0, device 0 (CE0)
spi.max_speed_hz = 1350000

def read_channel(channel):
    # MCP3008 read sequence
    adc = spi.xfer2([1, (8 + channel) << 4, 0])
    data = ((adc[1] & 3) << 8) + adc[2]
    return data

while True:
    value = read_channel(0)  # MQ sensor on CH0
    voltage = (value * 3.3) / 1023.0
    print(f"Raw: {value}, Voltage: {voltage:.2f} V")
    time.sleep(1)

Calibration Tips

Allow the sensor to preheat for the recommended time (often 24–48 hours for MQ series, check datasheet).
Record sensor output in clean air to establish a baseline value.
Expose the sensor to a known gas source (or higher concentration environment) to understand response range.
Use averaging or smoothing filters (moving average) in code to reduce noise.
For more accurate measurements, use the sensitivity curves in the datasheet and convert resistance ratio (Rs/R₀) to ppm.
Recalibrate periodically, especially if the sensor is used in harsh or dusty environments.

Maintenance Guidelines

Avoid exposing sensors to water, oil mist, or corrosive chemicals.
Do not touch the sensing element or metal mesh with bare hands.
Provide good airflow but protect from direct dust using a suitable enclosure or filter.
Power the heater (for MQ/MG811) according to the recommended voltage to avoid damage.
Check terminal connections regularly in industrial or high-vibration setups.
Replace sensors that show very slow response or cannot be calibrated reliably.

Troubleshooting

No change in readings: Check heater supply (for MQ/MG811), wiring and analog pin mapping.
Very noisy values: Use an analogRead averaging routine, shielded cables, and proper grounding.
Sensor always reads “high”: The environment may be contaminated; move to fresh air and allow time to recover.
Slow response or drift: Sensor may need more preheating or could be nearing end of life.
Raspberry Pi returns constant value: Verify MCP3008 wiring, SPI configuration, and CE pin selection.
Inconsistent values between boards: Calibrate each sensor individually and do not reuse R₀ values.

Buy Gas Sensor Module Online in India

Robocraze provides a wide range of Highly accurate gas sensors for Arduino, including oxygen, CO2, nitrogen, methane, and others natural gas detector. To detect gas leakage or the concentration of a specific gas in the air, use this portable toxic gas detection sensors.

Robocraze offers a wide range of gas sensors at the best prices, including popular models like MQ-2, MQ-4, MQ-5, MQ-7, MQ-3, MQ-131, MG811, and Fermion NO2, CO, H2S, NH3 detectors. Whether you're working on an air quality monitoring system, industrial safety project, or IoT application, you can find the right sensor to meet your needs. With fast shipping, easy returns, and reliable tech support, Robocraze ensures a seamless shopping experience for makers, students, and professionals.

Check out our collection of other sensors which can help in your upcoming electronic projects.

What is the Price of Gas Sensors in India?

Gas Sensors Price List	Cost
MQ-9 Gas Sensor Module	Rs.145
MQ-136 Hydrogen Gas Sensor	Rs.2129
MQ-3 Gas Sensor Module	Rs.116
MQ-8 Gas Sensor Module	Rs.110
MQ-5 Gas Sensor Module	RS.100
MQ-7 Gas Sensor Module	Rs.127
MQ-135 gas sensor Module	Rs.117
MQ-2 Gas Sensor Module	Rs.102
MQ-137 NH3 Gas Sensor Module	Rs.2156
MQ-6 Gas Sensor Module	Rs.115
MQ-4 Natural Gas Sensor Module	Rs.102
MG811 Carbon Dioxide Sensor	Rs.3306
MQ131 Ozone Gas Detection Module	Rs.1827
MQ-2 Gas Sensor	Rs.109

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1. Are gas detection sensors compatible with Arduino?

The output is an analog signal and can be read with an analog input of the Arduino. The MQ-2 Gas Sensor module is useful for gas leakage detecting in home and industry. It can detect LPG, i-butane, propane, methane, alcohol, hydrogen and smoke.

2. Where should Gas Detection Sensors be located?

Gas detectors should be placed near the floor for vapors or gases three or four times heavier than air. For the detection of lighter than air gases, sensors should be fitted near the roof or ceiling

3. What are the types of gas sensors?

Gas detection sensors are also called Gas Detectors. These sensors are electronic devices that detect and identify different types of gases. They are commonly used to detect toxic or explosive gasses and measure gas concentration.

4. How does a gas sensor work?

The working of a this sensor depends upon the concentration of the gas. Based on the concentration of the gas the sensor produces a corresponding potential difference by changing the resistance of the material inside the sensors, which can be measured as output voltage.

5. How does a smoke sensor module work?

Smoke alarms have a small amount of radioactive material between two electrically charged plates, which ionizes the air and causes current to flow between the plates. When smoke enters the chamber, it disrupts the flow of ions, thus reducing the flow of current and activating the alarm.

6. What are MQ2 and MQ3 gas detection sensors?

MQ2 gas detectors are also called as chemiresistors. It is an electronic sensor used for sensing the concentration of gases in the air such as LPG, propane, methane, hydrogen, alcohol, smoke and carbon monoxide. The MQ3 gas detection sensor is an alcohol sensor which is used to detect the alcohol concentration on your breath. These sensors provides an analog resistive output based on alcohol concentration.

7. What is the use of gas detectors?

The main purpose of Gas detectors or gas detectors help in detecting the different types of gases in the environment. They are commonly used to detect toxic or explosive gasses and measure gas concentration. Gas detectors can be used to detect combustible, flammable and toxic gases, and oxygen depletion. They may be used in firefighting.

8. What types of gases can these sensors detect?

The collection includes a wide variety of sensors designed to detect gases such as LPG, methane, natural gas, hydrogen, carbon monoxide, ozone, ammonia, nitrogen dioxide and air-quality pollutants. For example, some modules are specifically built for methane or LPG leak detection; others monitor broader air-pollution gases.

9. Are these sensors compatible with Arduino and Raspberry Pi?

Yes. These modules are built for hobby and DIY electronics, and many support analog outputs (that microcontrollers like Arduino can read) or digital trigger outputs. This makes them quite doable with both Arduino boards and Raspberry Pi setups (using its GPIO and ADC or external ADC modules).

10. What is the detection range and accuracy of these sensors?

Detection ranges vary by model. For instance, one methane sensor might specify a range from hundreds of parts per million (ppm) upward. The accuracy is suitable for general detection and safety alerting rather than ultra-precise scientific measurement. Users should expect approximate readings and often need calibration or threshold setting for reliable performance.

11. Can these sensors be used for safety monitoring and IoT projects?

Absolutely. These sensors are well suited for applications like gas-leak alarms, home safety systems, industrial IoT monitoring, air quality dashboards and environmental sensing. They integrate well into systems that alert users or send data when certain gases exceed thresholds.

12. Do these modules require calibration before use?

Yes — in most cases some calibration or baseline setup is needed. These sensors often require a “burn-in” or warm-up period, baseline measurement in clean air, and sometimes adjustment of sensitivity or threshold via a potentiometer. Calibration improves reliability when detecting specific gas concentrations in your environment.