MQ-7 CARBON MONOXIDE CO GAS SENSOR DETECTOR MODULE

This MQ-7 sensor module is a simple to use carbon monoxide (CO) sensor, suitable for detecting CO concentrations in the air.

The MQ-7 can detect CO gas concentrations anywhere from 10 to 1000ppm. Suitable for home and industrial use, it has fast response and recovery characteristics, long life and reliable stability.

The module features dual signal outputs: An analog output (0V to ~5V), the higher the gas concentration, the higher the voltage, and a digital TTL level output to signal the presence or absence of gas. The TTL threshold is adjustable with the onboard potentiometer.

MQ-7 Specifications:

• Operating voltage: 5 Volts DC (VCC Pin) for cleaning and measurement and 1.5V for heating 
• Maximum power consumption: 800mW (160mA at 5V)
• Dual signal output (analog (AO pin) and TTL (DO pin) level output)
  • TTL output signal is normally low, goes high when has is detected. Threshold is adjusted with the onboard potentiometer
  • 0 ~ 5V analog output voltage, the higher the concentration, the higher the voltage
• Indicator LEDs
  • Power
  • DO (Digital Output On)
• Detectable CO concentrations: 10-1000ppm 
• Dimensions (approximate): 32mm x 20mm x 27mm LxWxH (1.25 x 0.8 x 1.1 inches)
• Weight: 7 grams

MQ-7 Operation

There 4 leads that need to be connected to use the MQ-7. They are VCC (+5V or +1.4V), AOUT, DOUT, and GND.

The VCC and GND leads establish power for the sensor.

The other 2 leads are AOUT (analog output) and DOUT (digital output). The AOUT connector gives an analog voltage output in proportion to the amount of carbon monoxide the sensor detects. The more CO it detects, the greater the analog voltage it will output. Conversely, the less CO it detects, the less analog voltage it will output.

If the analog voltage reaches a certain threshold, it will send the digital pin DOUT high. This DOUT pin can be detected with an Arduino or other microcontroller and used to turn on an LED or other indicator, signaling that the CO threshold has been reached and is now over the limit.

Unlike the other MQ modules, in order to obtain the most accurate CO readings the MQ-7 will give the best results using the following cycle:

• Pre-heat the MQ-7 sensor for 48h at 1.5V
• Heat the heater with 5V for 60 seconds in order to expel any moisture (cleaning)
• Heat at 1.5V for 90 seconds to obtain the CO measurement
• The sensor should be read at 5V, but you don’t want to heat it up again, so near the end of the 90 seconds briefly increase the voltage to 5V again and read the sensor

You don’t actually need a true 1.5V at any given time, with a microcontroller such as an Arduino you can generate a PWM signal with an effective voltage (True RMS) of around 1.5V.

The video below describes this heating/measurement cycle. More details about it are on their website at https://www.areresearch.net/2017/03/detect-co-with-mq-7-sensor-module.html

On 5V alone, the module does work, but it will provide more accurate data following the procedure above.

The DOUT threshold level is adjusted using the onboard potentiometer to raise or lower the level.

Other Resources

How to use a MQ-7 carbon monoxide detector module video on Youtube:

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