Configure and read out the Raspberry Pi gas sensor (MQ-X)

Sensors are necessary to detect the components of the air. These are used e.g. in smoke detectors. However, instructions for using these gas sensors at the Raspberry Pi are rare, which is why in this tutorial the general use of such MQ modules at the Raspberry Pi is shown. Thus, e.g. smoke detectors or air quality testers can be built.

How to configure any MQ sensor and read it out with the Pi will be shown on the example of the Raspberry Pi gas sensor MQ2 in this tutorial. All other sensors (MQ3, MQ-135, etc.) can also be adapted with a few additional steps.

Accessories

All MQ-X sensors return analogue signals, which we can not easily read at the Raspberry Pi. One possibility would be to use an Arduino, but we can also use an analog-to-digital converter (ADC), which can be read out via the I2C bus. In addition, we also need a logic level converter.

Analog-Digital Converter (8 Ports): US / UK
5V to 3.3V Logic Level Converter: US / UK
Breadboard: US / UK
Jumper wire: US / UK

These components are independent of the selected gas sensor. There are also many different sensors for the Raspberry Pi, which are already available for a few bucks and are suitable for different gases:

MQ-2 (Methane, Butane, LPG, smoke): US / UK
MQ-3 (Alcohol, Ethanol, smoke): US / UK
MQ-4 (Methane, CNG Gas): US / UK
MQ-5 (Natural gas, LPG): US / UK
MQ-6 (LPG, butane gas): US / UK
MQ-7 (Carbon Monoxide): US / UK
MQ-8 (Hydrogen Gas): US / UK
MQ-9 (Carbon Monoxide, flammable gasses): US / UK
MQ-131 (Ozone): US / UK
MQ-135 (Benzene, Alcohol, smoke): US / UK
MQ-136 (Hydrogen Sulfide gas): US / UK
MQ-137 (Ammonia): US / UK
MQ-138 (Benzene, Toluene, Alcohol, Acetone, Propane, Formaldehyde gas): US / UK
MQ-214 (Methane, Natural gas): US / UK
MQ-216 (Natural gas, Coal gas): US / UK
MQ-303A (Alcohol, Ethanol, smoke): US / UK
MQ-306A (LPG, butane gas): US / UK
MQ-307A (Carbon Monoxide): US / UK
MQ-309A (Carbon Monoxide, flammable gasses): US / UK
MG811 (Carbon Dioxide (CO2)): US / UK
AQ-104 (air quality): US / UK
AQ-2 (Flamable gasses, smoke): US / UK
AQ-3 (Alcohol, Benzine): US / UK
AQ-7 (Carbon Monoxide): US / UK

You can find the full list with additional information here.

I recommend to use a sensor with a soldered PCB, because no further cabling and the use of resistors and capacitors is necessary.

Details on the individual Raspberry Pi gas sensors can also be found in the corresponding data sheets. Simply google the name of the sensor including “datasheet”. There is also the voltage at which the sensor operates mentioned.

If someone wants to build an alcohol tester or something similar, you should also be aware that these modules are not absolutely accurate and can not compete with a professional measurement.

Connection between MQ-2 and Raspberry Pi

In this example, we use a 5V voltage as output. This is too much for the GPIOs, which is why we use a logic level converter (TTL) that cuts down the voltage. If you use a sensor other than the MQ-2 and it has a different voltage, the setup must of course be adjusted.

After the MCP3008 is correctly connected, we use port 0 and connect it to RX0 of the TTL. On the opposite side is RX1, which is connected to the analog pin (A0) of the MQ2 sensor. Also connect 3.3V from the Raspberry Pi (LV) and 5V (HV) to the TTL. And also 5V to the VCC pin of the gas sensor and GND from the Raspberry Pi comes to GND on the LV and HV side of the TTL, as well as to GND of the MQ2.

Schematically the whole looks as follows:

I use the 5V of the Raspberry Pi’s. However, an external power supply is recommended if other sensors and modules or input devices (keyboard, mouse, touchscreen) are used. For this, the sensor is simply supplied with current from the external source (HV side of the TTL) and the ground connection (Minus / GND) is connected to GND of the Raspberry Pi.

Configuration of the Raspberry Pi Gas Sensor – Preparation

The concentration of a gas is given in PPM (parts per million). One difficulty of the MQ-2 is that a single analog value is given with which the gas content in the air has to be calculated for the various supported gases. However, the sensor must be configured for this purpose. Since this manual is also applicable to another Raspberry Pi gas sensor, the procedure is as follows:

First, we have to see the data sheet of the respective module, which contains a diagram:

The specified values are in logarithmic scale.

However, the scaling of the values is not linear but logarithmic to the base 10 (log). so, the first stroke on the X axis is 200, then 300, etc. The first stroke after 1000 is 2000, etc. The distance between is linear. The idea behind this script for calibration and reading is to create a straight line and calculate the amount of gas (in ppm). To do this, we need two points to calculate the slope.

Let us take the example of LPG. We therefore take the point P1 (x = 200, y = ~ 1.62) and P2 (x = 10000, y = ~ 0.26). To calculate the “real” values, we apply the ten logarithm. Using the two-point form, we can calculate the slope, which in our case is -0.47 (link to the calculation). With the slope and the calculated logarithm from the left point (x = 2.3, y = 0.21), we can now determine the straight line.

For the remaining gases the calculation is equivalent and can be carried out in the same way. Anyone who wants to have more reading material can do this here.

Calibration of the Raspberry Pi Gas Sensor – Code

Enough of the theory – we want to use the sensor now. For this purpose you can use the code I have customized, which is located in a GitHub repository. Also included is a class for reading the MCP3008. First we clone the directory:

git clone https://github.com/tutRPi/Raspberry-Pi-Gas-Sensor-MQ

Then we change to the directory and run the existing Python test file.

cd Raspberry-Pi-Gas-Sensor-MQ
sudo python example.py

The calibration is started automatically during initialization. It is important that the sensor is in good / fresh air as smoke / other gases would falsify the calibration. The process takes a few seconds, but the gas content can already be measured thereafter (see video). Some sensors are quite hot, but this should not be a cause for concern.

Some users reported that the values become accurate only after some time. I can not verify this, because I do not have a professional measuring device. If someone can confirm or verify, since he has such a device at home, I would be pleased about feedback as a comment 🙂

Featured

175 Responses

Aldiansyah 7-29-2017 at 2:49

I have thanks in raspberry programming for Gas sensor MQ 7 can i ask for help sir ?? Especially in entering calculations for CO gas

Reply
- Felix 7-29-2017 at 10:53
  
  If you want to use another sensor, you have to adjust the formula, depending on the sensor’s datasheet (cf. my example).
  
  Reply
  - lghtrr 2-16-2020 at 14:57
    
    hi, i’ve been fixed it for MQ138. but how about TGS2620 with just one curve for the main gas?
George 8-4-2017 at 23:36

Hello !
Thank you for your work ! Also I have a question.
Does the calibration have to be for 48 hours, does the sensor has to be pluged for 48 hours ? And how do you know the value of the load resistance ?

Reply
- Felix 8-5-2017 at 0:12
  
  Hi,
  usually the calibration needs about 10 seconds (enough precision for my applications). The value was given (you can change it, depending on your sensor).
  
  Reply
  - George 8-5-2017 at 13:42
    
    Thank you for your response 🙂 !
    I am using a MQ-7 sensor, do you happen to know what is the load resistance of it ? Or do you put it manualy in series with the sensor ? (in witch case it could be what you want)
  - Doubrapade Ikporukpo 9-23-2019 at 19:28
    
    Hi Felix, I am a student in University of Ibadan, Nigeria, working on an air quality project, please I need a Nitrogen oxide and Sulphur dioxide gas sensor that is compatible with the raspberry pi. Any suggestions on where to acquire these?
Konda Reddy Satya Narayana Reddy 8-8-2017 at 7:26

For my mq135 its giving Ro as 0 in the terminal

Reply
- Carolina Chaves 8-18-2017 at 5:45
  
  Hi, I also have a MQ135 sensor, I am having problems with programming it, can you help me? My email is: caroch1179@gmail.com
  
  Reply
  - Shivam Durgbuns 9-28-2017 at 17:39
    
    Please help me with sensor MQ135 & MQ7. I need for my project work. Any type of help is appreciated. 🙂
    email id : shivamdurgbuns@gmail.com
  - Tanvi 2-6-2019 at 8:53
    
    Can I also get for mq 135?
  - ho jin 4-8-2019 at 8:25
    
    Please help me with sensor MQ135. I need for my project work. Any type of help is appreciated. thank you
    My email is linghojin1996@gmail.com
Konda Reddy Satya Narayana Reddy 8-8-2017 at 7:29

Hi I’m using the same setup as yours and din’t change code also. But in the terminal i’m getting something like
“Press CTRL+C to abort.
Calibrating…
Calibration is done…

Ro=0.000000 kohm

Abort by user”
Please let me know what to do.

Reply
Ralph 11-8-2017 at 22:30

I keep getting this

pi@octopi:~/Raspberry-Pi-Gas-Sensor-MQ $ sudo python example.py
Traceback (most recent call last):
File “example.py”, line 1, in
from mq import *
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 6, in
from MCP3008 import MCP3008
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/MCP3008.py”, line 1, in
from spidev import SpiDev
ImportError: No module named spidev

Reply
- Felix 11-8-2017 at 23:27
  
  You have to install spidev…
  
  Reply
jesa javi 11-10-2017 at 4:53

Hi Can You Help Me Put Condition For Example Smoke Is Greater Than 1? then my buzzer will turn on..Its A Big Help For Me to Finish My Project..Godbless

Reply
syeda aiman 12-9-2017 at 18:59

i am not using mcp. i have directly connected the sensor to board without any converter.what kind of changes I have to do in code?

Reply
- Felix 12-10-2017 at 19:53
  
  It is not possible. You will need an ADC, as the Raspberry Pi cannot read analogue inputs.
  
  Reply
syeda aiman 12-9-2017 at 19:00

i need help i am not using mcp. i have directly connected the sensor to board without any converter.what kind of changes I have to do in code?

Reply
- Felix 12-10-2017 at 19:52
  
  If more than 3.3V are connected to the GPIOs, you can break them.
  
  Reply
Geraldy Martin 12-11-2017 at 6:58

Hello, im using mcp3002 instead mcp3008. What change should I made?

Reply
bobafett 12-17-2017 at 15:25

always show “Abort by user”, i’ll tried wiring like this tutorial and use code same on this. anyone can help?

Reply
- Felix 12-17-2017 at 16:06
  
  Log the exception.
  
  Reply
  - Shyam 1-29-2018 at 12:16
    
    Please say code sir
  - MOHD IDHAM BIN PODANG 10-2-2018 at 20:27
    
    how to log the exception?

Hi, I am using an ADS1115 analog to digital converter instead of MCP and MQ-2 sensor
My code is based on https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code

import time, signal, sys
from Adafruit_ADS1x15 import ADS1x15

ADS1115 = 0x01 # 16-bit ADC

# Select the gain
# gain = 6144 # +/- 6.144V
gain = 4096 # +/- 4.096V
# gain = 2048 # +/- 2.048V
# gain = 1024 # +/- 1.024V
# gain = 512 # +/- 0.512V
# gain = 256 # +/- 0.256V

# Select the sample rate
# sps = 8 # 8 samples per second
# sps = 16 # 16 samples per second
# sps = 32 # 32 samples per second
# sps = 64 # 64 samples per second
# sps = 128 # 128 samples per second
sps = 250 # 250 samples per second
# sps = 475 # 475 samples per second
# sps = 860 # 860 samples per second

# Initialise the ADCs using the default mode (use appropriate I2C address)
adc = ADS1x15(ic=ADS1115)
#adc2 = ADS1x15(ic=ADS1115, address=0x49)
#adc3 = ADS1x15(ic=ADS1115, address=0x4a)

# read analog sensor on channel Ax [0-3]
result = adc.readADCSingleEnded(1, gain, sps) / 1000

# print result
print "MQ-2: %.6f" % (result)

my return result is only one value for ex. 0.095875. Can you help me get those 4 values like yourself in the video (Ro, LPG, CO, smoke)?

Regards

syeda aiman 12-17-2017 at 18:20

i am using mcp3008 with mq2. but i am facing difficulty in wiring as my mcp has only 5 pins. So I am confuse what to do now.

Reply
- Felix 12-17-2017 at 20:45
  
  Probably it is no MCP3008
  
  Reply
- Dave 12-26-2017 at 1:27
  
  With only 5 pins I don’t think it could be a mcp3008. Google ‘mcp3008 datasheet’, and you’ll see that they all have the same layout. There’s a 3004 but even that has more pins than 5.
  
  Reply
Dave 12-26-2017 at 1:23

Sorry as I’m new, but I’m unsure of how this could work. Any documentation I can find on a logic level coverter says that they canot be used for analog conversions. They are only on/off. You’d have to take the output from the sensor and divide it using 2 resistors.

Reply
- Felix 12-27-2017 at 0:48
  
  That’s why we use the MCP3008 Analog Digital Converter.
  
  Reply
Meems 1-24-2018 at 22:25

I want to put an active buzzer in the project once the gas quality detected by the sensor get too high. In what part should I put the code for the buzzer?

Reply
brian burroughs 1-26-2018 at 15:10

have you a better diagram? mine aborts straight after running it.

Im not sure if i wired the vcc right, were you two red wires merge into one, I placed my sensor in the board and have the two wires in the same row as the vcc connection of the sensor

Reply
brian burroughs 1-26-2018 at 15:22

got it working, had the mcp3008 backwards

Reply
anand 1-31-2018 at 6:56

Hii frds iam anand….iam using mq135 sensor….i read the value from the sensor by raspberry but I want to sent the data to cloud…and I want sent msg to the particular person…so guys help me
My mail
Krishnan10497kmb@gmail.com

Reply
andrea 2-5-2018 at 0:19

el conversor de nivel logico lo conectan a la salida de dato analogo o digital?

Reply
Pazliquigan 2-16-2018 at 2:25

Hello Everyone.. Can you help us with our Capstone we are using a MQ-6 instead of MQ-2 is it posible that it had a the same output later? Thanks in advance

Reply
- Felix 2-16-2018 at 16:56
  
  Should be the same, but you have to adjust the formula!
  
  Reply
  - Paz 3-25-2018 at 20:40
    
    Press CTRL+C to abort.
    Calibrating…
    
    abort by user
    
    and im using mq6 sensor
    i got an error from this line of code can you please help me?
    def MQResistanceCalculation(self, raw_adc):
    return float(self.RL_VALUE*(1023.0-raw_adc))/float(raw_adc);
  - tripura 6-11-2019 at 9:01
    
    plz suggest the code ,where we have to update
  - Doubra 10-29-2019 at 9:11
    
    I’m using MQ135 please what do I adjust in the formulae. Also without the Logic Level Connverter could it work?
Christian 3-5-2018 at 6:20

Do you have codes please programming my mq 5 gas sensor to python using raspberry pi? Need much help about it.

Reply
- Felix 3-7-2018 at 22:44
  
  You can create it by using the datasheet. I have shown the way how the calculation works 🙂
  
  Reply
Jennifer 3-7-2018 at 20:28

Hi, I’m using an MQ135 and the only output I am seeing at the moment is:
Press CTRL+C to abort.

Abort by user
Is anyone experiencing something similar?
Thanks

Reply
- Felix 3-7-2018 at 22:43
  
  There is probably some exception thrown. You could log it to find out more.
  
  Reply
  - vikram 3-27-2019 at 8:33
    
    how can i log out
- MOHD IDHAM BIN PODANG 10-8-2018 at 18:39
  
  have u solve ur problem?
  
  Reply
- Dipendra B.C 4-20-2019 at 10:32
  
  I am also experiencing the same issue. Have you got any solutions??
  
  Reply
syauqi 3-8-2018 at 7:49

im using mq-2
output i get

Press CTRL+C to abort.
Calibrating…

Abort by user

Reply
syeda aiman 3-11-2018 at 10:57

may i connect 5v or 3.3v of pi with sensor mq2 and
im using mq-2
output i get

Press CTRL+C to abort.
Calibrating…

Abort by user

Reply
- Felix 3-11-2018 at 22:10
  
  Just log the exception.
  
  Reply
  - pieter fraser 3-12-2018 at 15:21
    
    how?
  - Felix 3-12-2018 at 19:57
    
    print()
anarchist18 3-14-2018 at 21:03

I have everything setup like in the tutorial, I’ve enabled exception logging in python:
Press CTRL+C to abort.
Calibrating…
ERROR:root:message
Traceback (most recent call last):
File “example.py”, line 7, in
mq = MQ();
File “/root/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 48, in __init__
self.Ro = self.MQCalibration(self.MQ_PIN)
File “/root/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 83, in MQCalibration
val += self.MQResistanceCalculation(self.adc.read(mq_pin))
File “/root/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 69, in MQResistanceCalculation
return float(self.RL_VALUE*(1023.0-raw_adc)/float(raw_adc));
ZeroDivisionError: float division by zero

Any ideas?

Reply
- Felix 3-17-2018 at 18:31
  
  Your ADC gives values of zero back, so probably there is something wront (check connections and read the value per hand)
  
  Reply
  - Laxman 2-9-2020 at 10:08
    
    I checked it but my mcp3008 giving some value but still facing same issue plz
Sunny 3-16-2018 at 13:03

Hi, i was getting error while running this code, so i commented the try and except,and started from while True:

after executing i got this error

Press CTRL+C to abort.
Calibrating…
Traceback (most recent call last):
File “example.py”, line 7, in
mq = MQ();
File “/home/pi/Desktop/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 48, in __init__
self.Ro = self.MQCalibration(self.MQ_PIN)
File “/home/pi/Desktop/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 83, in MQCalibration
val += self.MQResistanceCalculation(self.adc.read(mq_pin))
File “/home/pi/Desktop/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 69, in MQResistanceCalculation
return float(self.RL_VALUE*(1023.0-raw_adc)/float(raw_adc));
ZeroDivisionError: float division by zero

Reply
- Felix 3-17-2018 at 18:31
  
  Your ADC gives values of zero back, so probably there is something wront (check connections and read the value per hand)
  
  Reply
  - Sunny 3-19-2018 at 8:42
    
    with mcp3008 library my ADC is giving output
  - Felix 3-19-2018 at 21:49
    
    You can replace it by the other library.
  - Sunny 3-19-2018 at 8:43
    
    but with the code provided here, it is giving errors
  - Piotr Filarski 10-8-2018 at 21:30
    
    Sunny have you fixed it?
  - SB 11-16-2018 at 8:08
    
    I am getting the same error. I checked ADS1115 output and it is giving values for all 4 channels. Sample output mentioned here. But when running MQ2 example.py, it is giving same error. Please suggest how to check the signal coming from MQ2 sensor to ADS1115 is Ok.
    | 0 | 1 | 2 | 3 |
    ————————————-
    | 11516 | 4608 | 4793 | 4954 |
    | 11507 | 4832 | 4444 | 4941 |
    | 11502 | 4831 | 4450 | 4937 |
    | 11480 | 4773 | 4615 | 4641 |
    | 11529 | 4522 | 4827 | 4467 |
    | 11487 | 4485 | 4859 | 4375 |
    | 11515 | 4483 | 4863 | 4374 |
    | 11487 | 4491 | 4829 | 4481 |
    | 11499 | 4645 | 4744 | 4550 |
    | 11474 | 4751 | 4497 | 4926 |
    | 11461 | 4839 | 4443 | 4932 |
    | 11471 | 4844 | 4435 | 4961 |
    | 11497 | 4837 | 4440 | 4957 |
    | 11472 | 4819 | 4501 | 4789 |
    | 11497 | 4669 | 4628 | 4751 |
Jonas 3-20-2018 at 13:21

Hey, i ran the code and got

Press CTRL+C to abort.

Abort by user

then i tried to log the exception to figure out why it is not calibrating and than i got this error, pls help

Press CTRL+C to abort.

Abort by user
ERROR:root:message
Traceback (most recent call last):
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/example.py”, line 8, in
mq = MQ();
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 32, in __init__
self.adc = MCP3008()
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/MCP3008.py”, line 7, in __init__
self.open()
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/MCP3008.py”, line 10, in open
self.spi.open(self.bus, self.device)
FileNotFoundError: [Errno 2] No such file or directory

Reply
- Tinashe 3-20-2018 at 21:47
  
  I also have the same problem please assist.
  
  Reply
- Tinashe 3-20-2018 at 22:50
  
  Hie you need to enable the SPI interface. You can just google on how to do that
  
  Reply
ElDiller 3-21-2018 at 23:22

HI Felix thanks for your help and support. I.m having this errrr can you please help me..
pi@raspberrypi:~/Desktop/MQ2/Raspberry-Pi-Gas-Sensor-MQ $ sudo python example.pyPress CTRL+C to abort.
Traceback (most recent call last):
File “example.py”, line 14, in
mq = MQ();
File “/home/pi/Desktop/MQ2/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 32, in __init__
self.adc = MCP3008()
File “/home/pi/Desktop/MQ2/Raspberry-Pi-Gas-Sensor-MQ/MCP3008.py”, line 7, in __init__
self.open()
File “/home/pi/Desktop/MQ2/Raspberry-Pi-Gas-Sensor-MQ/MCP3008.py”, line 10, in open
self.spi.open(self.bus, self.device)
IOError: [Errno 2] No such file or directory

Thanks in advance..

Reply
- Felix 3-22-2018 at 0:36
  
  You have not enabled SPI or not installed SpiDev.
  
  Reply
- Shubham 3-23-2018 at 19:36
  
  see this repo https://github.com/shubham0490/MQ-sensor-ppm-conversion
  
  Reply
Shubham 3-23-2018 at 19:34

Hi, i was also getting the same errors but i have found the solution for this, check this link
https://github.com/shubham0490/MQ-sensor-ppm-conversion
There is problem with the library, install the adafruit library and the code which is in link will work fine

Reply
- ElDiller 3-25-2018 at 0:28
  
  thanks to both, I had several problems like not enabling the SPI but it still does not work, I’m trying now the other URL, thank you very much.
  
  Reply
  - ElDiller 3-25-2018 at 0:59
    
    New error
    Press CTRL+C to abort.
    Calibrating…
    Traceback (most recent call last):
    File “/home/pi/Desktop/MQ2/Raspberry-Pi-Gas-Sensor-MQ/examplewithdebug.py”, line 14, in
    mq = MQ();
    File “/home/pi/Desktop/MQ2/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 48, in __init__
    self.Ro = self.MQCalibration(self.MQ_PIN)
    File “/home/pi/Desktop/MQ2/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 83, in MQCalibration
    val += self.MQResistanceCalculation(self.adc.read(mq_pin))
    File “/home/pi/Desktop/MQ2/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 69, in MQResistanceCalculation
    return float(self.RL_VALUE*(1023.0-raw_adc)/float(raw_adc));
    ZeroDivisionError: float division by zero
- SB 11-13-2018 at 12:49
  
  I am facing the same problem and did not find specific solution for float division by zero error. Any suggestion is highly appreciated
  
  Reply
ElDiller 3-25-2018 at 1:05

ADC checked ..can you please confirm used port are 19,21,23 and 24_?

Reply
Shubham 3-26-2018 at 9:46

have you installed the Adafruit library? yup these ports are confirmed, i have also updated the github readme on this with videos

Reply
Shubham 3-27-2018 at 9:45

for pins refer to https://pinout.xyz

Reply
Faiz Mokti 3-28-2018 at 6:38

Press CTRL+C to abort.

Abort by user

the result after i run the example.py
any help?
im using putty

Reply
saad 3-28-2018 at 14:26

can i connect MQ-5 gas sensor to raspberry pi ? if yes can u pls show me the circuit ?

Reply
- Felix 3-28-2018 at 21:28
  
  Yes, the circuit is the same (use the analog output pin).
  
  Reply
  - qwertzuiop 4-7-2018 at 14:23
    
    but it does not work
Keelan 3-29-2018 at 16:46

Hello,
when I run the program it is immediately aborting by user after printing calibrating.
I have rebuilt the device a few times with different parts to minimize the potential for a broken piece. The errors that keep appearing are blank read adc values, no calibration and spi not available even though SpiDev has been enabled. while trying to run the program in Thonny IDE on the Pi, Errors keep appearing on lines 49,72, and 89. Any help would be greatly appreciated!

Reply
- Keelan 3-29-2018 at 23:15
  
  Turns out I had the ADC chip in backwards. The values are now starting to populate but the program will now randomly exit after only displaying values for a second or two.
  
  Reply
  - Faiz Mokti 4-1-2018 at 9:51
    
    how did you do it
Faiz Mokti 4-1-2018 at 9:56

this is my output
Press CTRL+C to abort.
Calibrating…

Abort by user

how to solve this

Reply
- vijaya 1-22-2019 at 15:44
  
  hello sir, had you got solution for this problem, i am also facing the same problem. could you suggest me sir!
  
  Reply
Svetlin 4-5-2018 at 18:28

Thank you Felix for this awesome tutorial, it helped me a lot! I admire your patience to answer all these Googleable questions.

Reply
shreya 4-11-2018 at 11:26

Please help me with sensor MQ135 & MQ7. I need for my project work. Any type of help is appreciated. ? shreyaghoradkar@gmail.com

Reply
osmanys 4-13-2018 at 5:02

i have problems
debugger
‘mq’._init_(), line 32:self.adc=MCP3008()
‘MCP3008’._init_(), line 7: self.spi.max_speed_hz=1000000 #1MHz
please i need help

Reply
Osmanys 4-22-2018 at 3:07

Como puedo conectar dos sensores mq al mismo raspberry pido saludos y gracias

Reply
Hemal 4-23-2018 at 2:29

unbound method read() must be called with MCP3008 instance as first argument (got int instance instead)

this is the error im getting what could be the fix

Reply
hemal 4-23-2018 at 2:30

unbound method read() must be called with MCP3008 instance as first argument (got int instance instead)

this is the problem im having

Reply
ElDiller 4-23-2018 at 4:44

Hi … I tell you that thanks to you my sensor works. My new question is. how could i conect another sensor, could it be done conecting it to other gate on the same to mc3008 gate, how should i modified the code .. some idea or suggestion

Reply
chuong 4-26-2018 at 1:53

Why don’t you use the digital output from the mq-2 sensor; but use the analog output + ADC?

Reply
- JeffD 9-19-2018 at 18:17
  
  Was just researching this as well, looks like the DO will only alert if gas is detected and wont give you specific values. You can only measure the amount of gas using analog output + converter
  
  Reply
Osmanys 4-28-2018 at 2:02

How can I change the configuration of the pins where the sensor is connected

Reply
Osmanys 4-28-2018 at 2:04

How can I connect two mq sensors to the same raspberry pi, please can someone help me with the code, thanks

Reply
JAY 5-20-2018 at 16:54

May i know how can you get the value of P1 (x = 200, y = ~ 1.62) —–1.62 from the datasheet?

Reply
- Osmanys 5-20-2018 at 22:51
  
  that result is from the table in the datasheet
  
  Reply
richard 5-30-2018 at 11:50

I am trying to setup a MQ-4 measuring Methane

self.CH4Curve = [2.3,0.24,-0.55] … my Winsen MQ-4 sensor spec indicates lg200 is 0.24 and lg10000 is 0.027 …through wolfram I get ( Log10(0.027) – log10(0.24) ) / ( log10(10000) – log10(200) ) = -0.558

how did you get the 2.3 value ?

Reply
Noor khokhar 6-29-2018 at 11:01

any one have code mq-135 sensor with pi In python code.

Reply
vishnu 6-29-2018 at 19:21

mq2 gas sensor can detect acetylene?
can you please suggest one to identify it.

Reply
Noor khokhar 7-2-2018 at 12:03

why we used MCP3008? i saw mq-135 sensor have already digital pin why we cannot direct digital pin.

Reply
- Veli 2-21-2019 at 18:30
  
  That digital pin is not a serial communication pin. On the sensor’s circuit board, there is a potentiometer setting a threshold value. If analog output is above that threshold value, digital output becomes high. If analog output is below that threshold value, digital output becomes low.
  
  This feature is for some basic diy circuits. For example, you can connect a LED to digital output pin. (There is a LED on the circuit board already 🙂 ) And you can set the potentiometer to a value that LED does not turns ON, in a clean air. If air goes bad (or whatever you name the situation), LED will turn ON after a gas density, depending your setting on potentiometer.
  
  Reply
Gurmeet Singh 7-23-2018 at 19:25

Hello sir,
I love this project and i want to make this project. You explain everything in this video but could you please provide me schematic diagram of this project?

Reply
marl 8-7-2018 at 17:36

i know the equation for -0.47

but

how do you get (x = 2.3, y = 0.21)?

Reply
nikko 8-23-2018 at 6:56

hello sir how will we get the slope for the given x and y?

Reply
Stas 9-25-2018 at 19:07

How about gas sensor for ethylene? is there any?

Reply
- Adrian 9-5-2019 at 15:28
  
  I am also interested in an ethylene gas sensor or one that at the very least has cross sensitivity.
  
  Reply
Invenisso 10-3-2018 at 22:04

My Ro=-0.213053 kohm. What’s wrong?

Reply
- peter 12-5-2019 at 20:42
  
  did you find a solution. I have same problem.
  
  Reply
Aashit Garodia 10-26-2018 at 10:30

Can you please explain me the code or If I can find the code explanation anywhere? Please help, have already googled everything about spidev.

from spidev import SpiDev

class MCP3008:
def __init__(self, bus = 0, device = 0):
self.bus, self.device = bus, device
self.spi = SpiDev()
self.open()
self.spi.max_speed_hz = 1000000 # 1MHz

def open(self):
self.spi.open(self.bus, self.device)
self.spi.max_speed_hz = 1000000 # 1MHz

def read(self, channel = 0):
cmd1 = 4 | 2 | (( channel & 4) >> 2)
cmd2 = (channel & 3) << 6

adc = self.spi.xfer2([cmd1, cmd2, 0])
data = ((adc[1] & 15) << 8) + adc[2]
return data

def close(self):
self.spi.close()

and if possible help me with this code too
https://github.com/tutRPi/Raspberry-Pi-Gas-Sensor-MQ/blob/master/mq.py

Reply
- Shreyansh 2-22-2019 at 6:35
  
  Did you get it?
  
  Reply
Aashit Garodia 10-26-2018 at 10:34

specifically this part of code:
cmd1 = 4 | 2 | (( channel & 4) >> 2)
cmd2 = (channel & 3) << 6

adc = self.spi.xfer2([cmd1, cmd2, 0])
data = ((adc[1] & 15) << 8) + adc[2]

PLEASE HELP

Reply
Theerapong 11-13-2018 at 18:00

This estimation of Rs/Ro from datasheet come with Big number of Error.

Reply
CMFR 1-30-2019 at 21:51

If I have a sensehat will I still be able to attach this or will I have to remove the sensehat? Is there some way to extend the pins or something?

Reply
vijaya 2-11-2019 at 10:50

Press CTRL+C to abort.
Calibrating…
Traceback (most recent call last):
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/example.py”, line 5, in
mq = MQ();
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 45, in __init__
self.Ro = self.MQCalibration(self.MQ_PIN)
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 80, in MQCalibration
val += self.MQResistanceCalculation(self.adc.read(mq_pin))
File “/home/pi/Raspberry-Pi-Gas-Sensor-MQ/mq.py”, line 66, in MQResistanceCalculation
return float(self.RL_VALUE*(1023.0-raw_adc)/float(raw_adc));
ZeroDivisionError: float division by zero

Reply
- Veli 2-21-2019 at 18:24
  
  Your ADC might be returning 4095.0 instead of 1023.0 for Maximum Analog Voltage, as in my case. First, connect 3.3 V to your channel 0 and print the ADC read value to the screen. After realizing a value ~4095, you should replace 1023.0 with 4095.0
  
  Reply
  - Shreyansh 2-22-2019 at 6:46
    
    Channel 0 is connected to RX0. So should we remove that connection?
  - Veli 2-25-2019 at 15:42
    
    You just need to test the digital value which is generated by the software and hardware both. You can use any of the ADC’s channels. You should connect a line(cable, etc, whatevery you call) to an ADC pin at a time.
    
    For your specific question: Yes you should remove that to measure the correct value.
Brady 2-20-2019 at 16:53

Did you find solution for negative Ro? I am having similar results with gases not being detected.

Reply
Veli 2-21-2019 at 18:21

Hi,
I realized that there is a little mistake on the code. In python math.log() takes log on base 2, not on base 10. math.log10() should be used for log based on 10.

“`
def MQGetPercentage(self, rs_ro_ratio, pcurve):
return (math.pow(10,( ((math.log(rs_ro_ratio)-pcurve[1])/ pcurve[2]) + pcurve[0])))
“`
Therefore the code above should be updated as like the below.

“`
def MQGetPercentage(self, rs_ro_ratio, pcurve):
return (math.pow(10,( ((math.log10(rs_ro_ratio)-pcurve[1])/ pcurve[2]) + pcurve[0])))
“`

Reply
- Shreyansh 2-22-2019 at 7:09
  
  Hi,
  I am doing this project with mq135. However when i print adc in the following code
  def read(self, channel = 0):
  cmd1 = 4 | 2 | (( channel & 4) >> 2)
  cmd2 = (channel & 3) << 6
  
  adc = self.spi.xfer2([cmd1, cmd2, 0])
  print(adc)
  data = ((adc[1] & 15) << 8) + adc[2]
  return data
  I get a list of 0 like[0 0 0]. Due to this I am getting a divided by 0 error. What can I do to resolve it?
  
  Reply
  - Veli 2-25-2019 at 15:48
    
    Could you please check your connections? Do not forget ALL OF THE 8 pins of MCP3008 which are on the opposite side of the channel pins. After being sure of this, check return value again. If the problem still occurs, instead of sensor output, connect 3.3 V to a channel and check the printed value again.
- dewi 2-12-2020 at 5:02
  
  how is its gonna be only 1 curve ? i’m using TGS how the code “def … percentage” should be ?
  
  Reply
Veli 2-25-2019 at 15:49

“ALL OF THE 8 pins of MCP3008 which are on the opposite side of the channel pins” should be connected. Do not skip any of them.

Reply
Shreyansh 3-13-2019 at 13:05

Hi,
Thanks for you help.
I checked for the values after connecting 3.3V I was getting 1023 constantly. Yet the program is aborting

Reply
Dan 3-13-2019 at 13:11

I followed all the steps and when I type sudo python example.py it says abort by user even though I did not abort. How can this be fixed?

Reply
Harish Sakthi 3-24-2019 at 16:10

I am trying to do a project where I am utilizing multiple gas sensors. I know that the MCP3008 can support 8 devices at once, but I have read in forums that the Raspberry Pi can only handle 2 SPI slaves. I have made gas sensors multiple circuits utilizing one MCP3008 and TTL, so will that work? (They are soldered circuits). I have already utilized one of those circuits and that works fine. I have a GPIO expansion board with three GPIO pin headers, so I have 120 pins to utilize, all with the same layout as the normal pin header. If not, could I connect 8 sensors to one MCP3008? And what kind of changes would I need to make to MCP3008?

Reply
Harish Sakthi 3-24-2019 at 16:13

Sorry, I meant MCP3008.py.

Reply
Manj 3-29-2019 at 8:03

“Abort by user” is being displayed. Anything you can help?

Reply
- Giovanni 4-30-2019 at 11:55
  
  I have the same problem. Have you solved?
  
  Reply
  - Laxmam 2-9-2020 at 10:18
    
    Have u got the solution plz contact me
    On this email laxmanrathod455@gmail.com
pec 4-7-2019 at 10:35

I’m trying to understand why logic level converter is needed between ADC (MCP3008) and MQ sensor.

according to this comment
https://www.raspberrypi.org/forums/viewtopic.php?t=189209#p1191345
there is no need for that and IMHO this comment makes sense.

Reply
Bernhard 5-1-2019 at 23:16

Hi, I’m just try to get it running.
The error-messages say, that “no module named spidev”
Ok, I checked that on the net, using
mkdir python-spi
cd python-spi
wget https://raw.github.com/doceme/py-spidev/master/setup.py
wget https://raw.github.com/doceme/py-spidev/master/spidev_module.c sudo python setup.py install

ending up with the following message:
Traceback (most recent call last):
File “setup.py”, line 29, in
long_description= open(‘README.md’).read() + “n” + open(‘CHANGELOG.md’).read(),
IOError: [Errno 2] No such file or directory: ‘README.md’

Unfortunately I did not find a suitable solution on the net.

Do you have any suggestions?

Best regards

B.

Reply
Aju Varghese Antony 5-8-2019 at 9:56

Hi,
I am using ARPI600 on my RPI as ADC, can you tell me what changes I will have to make for MQ-137 and MQ-135 to get it work?
It will be of great help

arpi600 https://www.waveshare.com/wiki/ARPI600

Reply
Shrikanth Singh 6-24-2019 at 9:53

Does the code work for Python 3 too?

Reply
marco 10-10-2019 at 14:57

from the python code is calculated only GAS LNG, CO and SMOKE, to get the values of others (H2, air, propane, alcohol, etc.) is it enough to add in the class class MQ () the calculated points?

Reply
Colleen 10-11-2019 at 16:13

It worked for me! Thank you so much. Is it possible though to have Mathematica read off the sensor (instead of concentration displaying in the terminal?) Thanks!

Reply
nemo 11-26-2019 at 7:00

I followed all the steps given but why does the value of resistance is negative?

Press CTRL+C to abort.
Calibrating…
Calibration is done…

Ro=-0.231164 kohm

LPG: 0.0076744 ppm, CO: 0.00497707 ppm, Smoke: 0.0204785 ppm

and there is no change on the value when I spray some lighter gas on the sensor

Reply
- peter 12-5-2019 at 20:52
  
  I encounter the same problem. when gas/smoke is added, the values go down! Must be something in “example.py”?
  Ro=-0.247752
  LPG: 0.00542804 ppm, CO: 0.00308366 ppm, Smoke: 0.0141463 ppm
  
  Reply
- peter 12-5-2019 at 20:53
  
  I encounter the same problem. when gas/smoke is added, the values go down! Must be something in “example.py”?
  Ro=-0.247752
  
  Reply
  - Laxman 2-9-2020 at 10:24
    
    Hi bro I also refer the same git hub code but I am facing divide by zero. Error exception
    As u said you are getting some value atleast plz contact me or help me
    Thanks is advance
    On this email id
    laxmanrathod455@gmail.com
FatihN 12-14-2019 at 18:46

I’m getting error on MQ-5

Press CTRL+C to abort.
Calibrating…
float division by zero

Why?

Reply
Alexander Schmid 12-19-2019 at 18:18

Hi! First: THANK YOU VERY MUCH for your great work!

I was using your wiring and code with a MQ-5 and it worked fine! However, when I changed the MQ-5 with a MQ-2 – the same sensor you are using – I get a strange behaviour: LPG and CO values drop when the sensor is exposed to LPG / CO instead of rising which means, the values are going down to an e-05 value… Do you have any explanation for this? Do I need to do a 1 / [value] calculation to correct that?

THANK YOU!

Reply
- Alexander Schmid 12-19-2019 at 18:19
  
  (and yes, I already tried another MQ-2 sensor)
  
  Reply
gas detector 12-26-2019 at 6:47

Thanks for having this article, it helps a lot. It’s a well-written blog and it is very informative. Keep on blogging, looking forward to see more of your posts!

Reply
Naveen 1-29-2020 at 6:56

Hi, actually i am using raspberry pi 3b+
i need a help on MQ3 and ADC
How to install and how to run the program….?

Reply
Ching 1-31-2020 at 17:32

Hiii, does anyone know how to get (x=2.3, y=0.21) for the calibration?

Reply
- Ching 1-31-2020 at 17:39
  
  ooo silly me! its log(200)=2.3 and log(1.62)=0.21
  
  Reply

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Controlling the Raspberry Pi RTC Module – I2C Real Time Clock

Raspberry Pi LCD Touch Display Part 2 – Adjustments

LCD Touch Display (3.2″) on the Raspberry Pi

Raspberry Pi Zero – Establishing an Ethernet connection (ENC28J60)

How to let an Arduino and Raspberry Pi communicate with each other

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Configure and read out the Raspberry Pi gas sensor (MQ-X)

Accessories

Connection between MQ-2 and Raspberry Pi

Configuration of the Raspberry Pi Gas Sensor – Preparation

Calibration of the Raspberry Pi Gas Sensor – Code

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175 Responses

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50 of the most important Raspberry Pi Sensors and Components

Using a Raspberry Pi distance sensor (ultrasonic sensor HC-SR04)

How to setup a Raspberry Pi Security Camera Livestream

How to get Google Chromium for the Raspberry Pi

Connect and Control WS2812 RGB LED Strips via Raspberry Pi

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