MQ135 Alcohol Sensor Circuit And Working

The MQ series of gas sensors utilize a small heater inside with an electrochemical sensor these sensors are sensitive to a range of gasses are used at room temperature. MQ135 alcohol sensor is a Sno2 with a lower conductivity of clean air. When the target explosive gas exists, then the sensor’s conductivity increases more increasing more along with the gas concentration rising levels. By using simple electronic circuits, it converts the charge of conductivity to correspond output signal of gas concentration

The MQ135 gas sensor has high sensitivity in ammonia, sulfide, benzene steam, smoke, and in other harm full gas. It is low cost and suitable for different applications. There are different types of alcohol sensors like MQ-2, MQ-3, MQ-4, MQ-5, MQ-6,  etc.

What is an Alcohol Sensor?

An alcohol sensor detects the attentiveness of alcohol gas in the air and an analog voltage is an output reading. The sensor can activate at temperatures ranging from -10 to 50° C with a power supply is less than 150 Ma to 5V. The sensing range is from 0.04 mg/L to 4 mg/L, which is suitable for breathalyzers.

Alcohol Sensor
Alcohol Sensor

MQ-135 Gas Sensor

The MQ-135 gas sensor senses gases like ammonia nitrogen, oxygen, alcohols, aromatic compounds, sulfide, and smoke. The boost converter of the chip MQ-3 gas sensor is PT1301. The operating voltage of this gas sensor is from 2.5V to 5.0V. The MQ-3 gas sensor has a lower conductivity to clean the air as a gas sensing material. In the atmosphere, we can find polluting gases, but the conductivity of the gas sensor increases as the concentration of polluting gas increases. MQ-135 gas sensor can be implemented to detect the smoke, benzene, steam, and other harmful gases. It has the potential to detect different harmful gases. The MQ-135 gas sensor is a low cost to purchase. The basic image of the MQ-135 sensor is shown in the below figure.

MQ-135 Gas Sensor
MQ-135 Gas Sensor

Basic Pin Configuration Of Alcohol Sensor

The MQ-3 alcohol gas sensor consists of a total 6-pins including A, H, B, and the other three pins are A, H, B out of the total 6-pins we use only 4 pins. The two pins A, H are used for the heating purpose and the other two pins are used for the ground and power. There is a heating system inside the sensor, which is made up of aluminum oxide, tin dioxide.  It has heat coils to produce heat, and thus it is used as a heat sensor. The below diagram shows the pin diagram and the configuration of the MQ-3 alcohol sensor.

Pin Configuration Of Alcohol Sensor
Pin Configuration Of Alcohol Sensor

Working Principle And Circuit Diagram

The MQ-135 alcohol sensor consists of a tin dioxide (SnO2), a perspective layer inside aluminum oxide microtubes (measuring electrodes), and a heating element inside a tubular casing. The end face of the sensor is enclosed by a stainless steel net and the backside holds the connection terminals. Ethyl alcohol present in the breath is oxidized into acetic acid passing through the heating element. With the ethyl alcohol cascade on the tin dioxide sensing layer, the resistance decreases. By using the external load resistance the resistance variation is converted into a suitable voltage variation. The circuit diagram and the connection arrangement of an MQ 135 alcohol are shown below.


MQ-135 Circuit Diagram
MQ-135 Circuit Diagram

MQ – 135 Air Quality Sensor

The air quality sensor is also an MQ-135 sensor for detecting venomous gases that are present in the air in homes and offices. The gas sensor layer of the sensor unit is made up of tin dioxide (SnO2); it has lower conductivity compare to clean hair and due to air pollution the conductivity is increased. The air quality sensor detects ammonia, nitrogen oxide, smoke, CO2, and other harmful gases. The air quality sensor has a small potentiometer that permits the adjustment of the load resistance of the sensor circuit. The 5V power supply is used for air quality sensor.

MQ – 135 Air Quality Sensor

The air quality sensor is a signal output indicator instruction. It has two outputs: analog output and TTL output. The TTL output is low signal light which can be accessed through the IO ports on the Microcontroller. The analog output is a concentration, i.e. increasing voltage is directly proportional to increasing concentration. This sensor has a long life and reliable stability as well.

Applications Of MQ 135 Gas Sensor

The following are the applications of the MQ 135 gas sensor:

  • Air quality monitor
  • Detection of harmful gases
  • Domestic air pollution detection
  • Industrial pollution detection
  • Portable air pollution detection

Characteristics Of MQ 135

  • Good sensitivity to harmful gases in a wide range.
  • It has a long life and low cost.
  • Possesses high sensitivity to ammonia, benzene, sulfide gases.
  • It is a simple drive circuit

This is about the MQ135 alcohol sensor circuit diagram and the working operation and its applications. We hope that the given information in the article is helpful to you in gaining some good knowledge and understanding of the project. Furthermore, if you have any queries regarding this article and on electrical and electronic projects, you can comment in the below section. Here is a question for you: How to find a Co2 and O2 level using MQ135 Arduino?

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  1. How can i find the type of gas and its concentration just by reading its voltage?

    1. Tarun Agarwal says:

      Hi Manju
      Semiconductor sensor is used to detect various kinds of gases namely oxygen, Hydrogen, the vapor of alcohol, and harmful gases like carbon monoxide. This sensor is most useful in carbon monoxide sensors, which are used in breathalyzers.

  2. At the moment I ask myself the same question, which is mentioned at the end: How can I measure only one of the gases for the MQ135 and have the values displayed, e.g. for CH4 or NOx?

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