High readings from gas sensor (MQ131)

[rihamk]

Hi, I've been experimenting with high concentration ozone gas sensor MQ131 for a university project. I followed the datasheet before running the sensor, it required warming up (connecting it to 5v supply for over 48hrs) and run some code to get readings.
I took the readings in my room so I was not expecting to get such high (hazardous) readings:

I used this library and got the code from it as reference for testing.
Any idea why I would get these readings? Do I need to let it warm up more?

[jremington]

If the result is similar after another 48 hours of burn-in, try another MQ-131.

[rihamk]

I have 2 MQ131 sensors, I followed the same procedure for both of them but still got the same results for both

[jremington]

Please post a hand drawn wiring diagram, and your code, using code tags.

Make sure that the heater power supply is exactly 5V (it is not a good idea to use the Arduino 5V output, as it is not designed for that large current).

[wildbill]

I've read (here?) that the range of MQ sensors as a whole are not particularly accurate. Also, that they are triggered by multiple gases, so you may have something else in your room masquerading as ozone.

[jremington]

Good point. Dirty socks?

This is an excellent resource for the MQ sensors: https://web.archive.org/web/20180513090020/http://www.maskau.dk/projects/electronic-nose

[rihamk]

This is the sensor that I'm using, I got it from aliexpress: https://www.aliexpress.com/item/1005003784095876.html?spm=a2g0o.productlist.0.0.78f26405CyNtJX&algo_pvid=2219121d-8919-40f8-91ad-2f553645f43c&algo_exp_id=2219121d-8919-40f8-91ad-2f553645f43c-2&pdp_ext_f={"sku_id"%3A"12000027157424382"}&pdp_npi=2%40dis!BHD!!3.72!!!!!%400bb0620316527966116351722e956a!12000027157424382!sea

My code:

#include "MQ131.h"

void setup() {
  Serial.begin(115200); //115200

  // Init the sensor
  // - Heater control on pin 2
  // - Sensor analog read on pin A0
  // - Model LOW_CONCENTRATION
  // - Load resistance RL of 1MOhms (1000000 Ohms)
  MQ131.begin(2,A0, HIGH_CONCENTRATION, 1000000);  

  Serial.println("Calibration in progress...");
  
  MQ131.calibrate();
  
  Serial.println("Calibration done!");
  Serial.print("R0 = ");
  Serial.print(MQ131.getR0());
  Serial.println(" Ohms");
  Serial.print("Time to heat = ");
  Serial.print(MQ131.getTimeToRead());
  Serial.println(" s");
}

void loop() {
  Serial.println("Sampling...");
  MQ131.sample();
  Serial.print("Concentration O3 : ");
  Serial.print(MQ131.getO3(PPM));
  Serial.println(" ppm");
  Serial.print("Concentration O3 : ");
  Serial.print(MQ131.getO3(PPB));
  Serial.println(" ppb");
  Serial.print("Concentration O3 : ");
  Serial.print(MQ131.getO3(MG_M3));
  Serial.println(" mg/m3");
  Serial.print("Concentration O3 : ");
  Serial.print(MQ131.getO3(UG_M3));
  Serial.println(" ug/m3");

  delay(30000);
}

Another code I tried and still got high readings:

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

}

void loop() 
{
  float value4 = analogRead(A0);
  float sensorValue4;
  sensorValue4 = (value4 / 2) / 1000;
  Serial.println(sensorValue4);
  delay(30000);
}

[rihamk]

lol perhaps (jk)
the link does not work for me..

[jremington]

You have no way of knowing what you get from Aliexpress.

[TomGeorge]

Hi,

What does the trimpot do, set threshold for digital output?

Where you have pin2 connected to is the digital OUTPUT of the module, not heater control.
Reverse engineer the module and see what it is connected too.

Main chip: LM393, MQ-131 gas sensor

This may help;
mq131-datasheet-low.pdf (663.9 KB)

Tom....

[rihamk]

Thank you for responding, I'm not 100% sure but I think the trimpot is just for adjusting the sensitivity of the sensor maybe.
So I need to connect the digital output to heater control? but where is the heater control in arduino?

[TomGeorge]

@rihamk

I'm not 100% sure but I think the trimpot is just for adjusting the sensitivity of the sensor maybe.
So I need to connect the digital output to heater control? but where is the heater control in arduino?

The pot I think you will find is to set the threshold of what reading the digital output changes state.
That module has NO heater control. What data are you using to indicate that it has.

Read the datasheet link I posted in post #10.

Can you please tell us your electronics, programming, arduino, hardware experience?

Thanks.. Tom...
PS. I'm off to bed its 12:50am here....

[rihamk]

From what I understand, the heater should be controlled by N-channel MOSFET, I understand now that this module has no heater control, but does that have anything to do with the readings I'm getting? Like does the heater control affect the readings? If it does, do you have an idea of how I could change my circuit connection because I don't fully understand what I'm supposed to do..

I'm in my final year in taking my Bachelors degree in electronics engineering, my final year project is to produce an air pollution warning system and this is one of the sensor modules that I will be using. I've done some programming projects and circuit designing projects, I also have taken a course where we had done a bunch of experiments using the Arduino.

[wildbill]

You just need to power the heater. Looking at the datasheet @TomGeorge provided, depending on how your Arduino is powered, it may be marginal. That's where the idea of using a MOSFET came from I expect, so that you can provide heater power separately.

[jremington]

If the heater is not properly heating, the module won't work at all.

[rihamk]

I will attempt that, I removed the sensor from the module and will try connecting it the same way as the circuit shown in the datasheet