MQ-8 Hydrogen/H2 Sensor Module

Overview

This sensor module has an MQ-8 as the sensor component and has a protection resistor and an adjustable resistor on-board. The MQ-8 gas sensor is highly sensitive hydrogen and less sensitive to alcohol, and cooking fume. It could be used in gas leakage detecting equipments in family and industry. The resistance of the sensitive component changes as the concentration of the target gas changes.

Features

  • Continuous Analog output
  • 3-pin interlock connector
  • Low cost and compact size

Standard Working Condition

Symbol Parameter Name Technical Condition Remarks
VC Circuit voltage 5V±0.1 AC or DC
VH Heating voltage 5V±0.1 AC or DC
RL Load resistance 10Kohm
RH Heater resistance 31Kohm±5% Room temperature
PH Heating consumption Less than 800mW

Environment Condition

Symbol Parameter Name Technical Condition Remarks
TO Operating Temp. -10°C-50°C
TS Storage Temp. -20°C-70°C
RH Relative Humidity <95%
O2 Oxygen Concentration 21%(standard condition) Oxygen concentration can affect sensitivity Minimum value is 2%

Sensitivity Characteristics

Symbol Parameter Name Technical Condition Remarks
RS Sensor Resistance 10Kohm-60Kohm (1000ppm LPG) Detecting concentration Scope: 100-10000ppm H2
α (1000ppm/4000ppm H2) Concentration slope rate ≤0.6
Standard detecting Condition Temp.: 20°C±2°C VC: 5V±0.1
Humidity:65%±5% VH:5V±0.1
Preheating Time Over 24 hours

Typical Application Schematics

typical_app

Theory

The protection resistor (5.1Kohms) and the adjustable (0-50Kohms) are in serial which forms a load resistor RL (5.1-55.1Kohms). The sensor’s resistance RS and RL forms a voltage divider. The output voltage on the signal pin could be read by Arduino or MCU via ADC.  Given a value of RL, Power Supply Voltage, and output voltage, RS could be derived.  Based on the chart provided in the MQ-8 datasheet, RS in clean air under given temperature and humidity is a constant, which is the “initial” resistance of the sensor named RO. RO of the resistor could be derived from RS. The main job of the calibration is to calculate the RO by sampling and averaging the readings when the module is placed in the clean air. Once the RO is derived, the concentration of target gas could be calculated by using the RS/RO ratio as the input. To achieve more accuracy, a segmented look-up table should be used. However, in the demonstration, a linear formula is used as an approximation to the original curve.

Arduino Sample Code

Demo Output

SEN-000008.demoDemo output as the sensor approaches the cathode of NaOH solution under electrolyzation

Dimensions

dimensions

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5 thoughts on “MQ-8 Hydrogen/H2 Sensor Module

    1. Then it should be (lg200, lg8.5) and (lg10000, lg0.03). Thank you to point this out, and I have updated the datasheet. :)

  1. Hey,

    What environment did you use to find the Ro value? This is supposed to be the resistance in clean air, so I was wondering if you put it anywhere or made anything specific to find this.

    Thanks,

    Corey

    1. Just put it outside the window should be fine, the “clean air” is defined that there is no material in the air which will affect the output of the sensor.

      1. Thank you. I have one more question. Because there is a preheat time of over 24 hours, should the Ro value be determined after the sensor is completely heated (reached steady state)? If it isn’t determined after this, drift will occur to your sensor values due to the heating up of the sensor, and not because difference in gas concentrations

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