mh-z19 3.1.1

mh-z19 CO2 concentration sensor library for All models of Raspberry Pi

mh-z19

Read CO2 concentration from mh-z19 sensor

install

pip install mh_z19

installs

how to use

Use as python script.

pi@raspberrypi:~/mh-z19/pypi $ sudo python -m mh_z19
{'co2': 500}

Import module and call read()

pi@raspberrypi:~/mh-z19/pypi $ sudo python
Python 2.7.13 (default, Nov 24 2017, 17:33:09) 
[GCC 6.3.0 20170516] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import mh_z19
>>> mh_z19.read()
{'co2': 477}
>>> 

The sudo might be necessary because mh_z19 module use Serial.

The differences of the interface between each Raspberry Pi model are resolved inside this module. For example, serial device name is difference between Raspberry Pi 3 and older model, but mh-z19 module automatically detect the model and read from appropriate serial device.

To use mh-z19, once you need to set up enabling serial port device on the Raspberry Pi. Following Wiki page might be informative.

cabling

Connect RPi & mh-z19 as:

• 5V on RPi and Vin on mh-z19
• GND(0v) on RPi and GND on mh-z19
• TxD and RxD are connected to cross between RPi and mh-z18

Followings are example of cabling, but you can free to use other 5v and 0v Pin on the RPi.

pi@raspberrypi:~/mh-z19 $ gpio readall
 +-----+-----+---------+------+---+---Pi B+--+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 |     |     |    3.3v |      |   |  1 || 2  |   |      | 5v      |     |     |
 |   2 |   8 |   SDA.1 |   IN | 1 |  3 || 4  |   |      | 5v      |     |     |  <---- Vin
 |   3 |   9 |   SCL.1 |   IN | 1 |  5 || 6  |   |      | 0v      |     |     |  <---- Gnd
 |   4 |   7 | GPIO. 7 |   IN | 1 |  7 || 8  | 1 | ALT0 | TxD     | 15  | 14  |  <---- RxD
 |     |     |      0v |      |   |  9 || 10 | 1 | ALT0 | RxD     | 16  | 15  |  <---- TxD
 |  17 |   0 | GPIO. 0 |   IN | 0 | 11 || 12 | 0 | IN   | GPIO. 1 | 1   | 18  |
 |  27 |   2 | GPIO. 2 |   IN | 0 | 13 || 14 |   |      | 0v      |     |     |
 |  22 |   3 | GPIO. 3 |   IN | 0 | 15 || 16 | 0 | IN   | GPIO. 4 | 4   | 23  |
 |     |     |    3.3v |      |   | 17 || 18 | 0 | IN   | GPIO. 5 | 5   | 24  |
 |  10 |  12 |    MOSI |   IN | 0 | 19 || 20 |   |      | 0v      |     |     |
 |   9 |  13 |    MISO |   IN | 0 | 21 || 22 | 0 | IN   | GPIO. 6 | 6   | 25  |
 |  11 |  14 |    SCLK |   IN | 0 | 23 || 24 | 1 | IN   | CE0     | 10  | 8   |
 |     |     |      0v |      |   | 25 || 26 | 1 | IN   | CE1     | 11  | 7   |
 |   0 |  30 |   SDA.0 |   IN | 1 | 27 || 28 | 1 | IN   | SCL.0   | 31  | 1   |
 |   5 |  21 | GPIO.21 |   IN | 1 | 29 || 30 |   |      | 0v      |     |     |
 |   6 |  22 | GPIO.22 |   IN | 1 | 31 || 32 | 0 | IN   | GPIO.26 | 26  | 12  |
 |  13 |  23 | GPIO.23 |   IN | 0 | 33 || 34 |   |      | 0v      |     |     |
 |  19 |  24 | GPIO.24 |   IN | 0 | 35 || 36 | 0 | IN   | GPIO.27 | 27  | 16  |
 |  26 |  25 | GPIO.25 |   IN | 0 | 37 || 38 | 0 | IN   | GPIO.28 | 28  | 20  |
 |     |     |      0v |      |   | 39 || 40 | 0 | IN   | GPIO.29 | 29  | 21  |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+---Pi B+--+---+------+---------+-----+-----+

Watch CO2 concentration on your browser

MONITOR™ is a free Remote Monitoring Service to show latest data on the web. You can see the current CO2 concentration value measured by your MH-Z19 device on your smartphone. For detail, please refer this blog.

Calibration, Detection range settings, and ABC(Automatic Baseline Correction) logic on/off.

Features about calibration (both MH-Z19 & MH-Z19B), detection range change (MH-Z19B) and ABC logic on/off(MH-Z19B) are implemented at version 0.2.1 or later.

I'm afraid I've just only implemented these without test due to lack necessary devices and apparatus for the test, fx: standard concentration CO2 gas, also MH-Z19B module. If you have these devices or apparatus and try to use these functions generously, I'm really appreciate your issue report regardless result were positive or negative.

For detail please refer this wiki.

Undocumented response values of 0x86 command.

The Revspace/MHZ19 shows values undocumented on the official datasheets(MH-Z19, MH-Z19B). In accordance with this, --all option add these values in the return json value as follows:

sudo python -m mh_z19 --all
{"SS": 232, "UhUl": 10752, "TT": 61, "co2": 818, "temperature": 21}

sudo python3 -m mh_z19 --all
{"TT": 61, "co2": 807, "SS": 232, "temperature": 21, "UhUl": 10752}

or call read_all() function as follows:

>>> import mh_z19
>>> mh_z19.read_all()
{'SS': 232, 'UhUl': 10738, 'TT': 61, 'co2': 734, 'temperature': 21}
>>> 

Use specific serial device.

In case you should use specific serial device insted of Raspberry Pi default serial device which this library automatically select, for example in case to need to use /dev/ttyUSB0 for FT232 usb-serial converter as issue#12, you can specify serial device by --serial_device option as follows:

sudo python -m mh_z19 --serial_device /dev/ttyUSB0

How to use without root permission.

See this wiki.

How to use in your program.

See this wiki.

PWM support.

See this wiki.

In case you can't get the value.

Even if cabling seems no problem and uart seems to be prepateted well but you can't get sensor value. As nincube8 suggested that the pull up by 1-5kΩ register can be working solution. Thank you nincube8!

Q&A

The forum is avai at here. Any questions, suggestions, reports are welcome!

Blog

• How to Measure ROOM CO2 concentration with 20$ sensor "MH-Z19" and Raspberry Pi.
• Monitoring all over the world with 3G Network for not more than 10$ monthly payment.
• How to make shareable SD card by Raspberry Pi & PC.

References

• MH-H19B DataSheet version 1.5
• MH-H19 DataSheet version 1.0
• MH-H19B DataSheet version 1.0
• RevSpace

history

• 0.1.1 2018.11.05 first version self-forked from slider.
• 0.1.3 2018.11.06 fix Readme.
• 0.1.4 2018.11.15 revise Readme.
• 0.1.6 2018.11.29 revise Readme.
• 0.2.1 2019.01.18 add followings without test (sorry) abc_on(), abc_off(), span_point_calibration(), xero_point_calibration(), detection_range_5000(), detection_range_2000(), checksum()
• 0.3.5 2019.01.22 Both Python2 & Python3 support
• 0.3.6 2019.01.22 Merge Pull Request #3 & Pull Request #4. Thanks David!
• 0.3.7 2019.02.25 Add --all option which requested as issue#5, thanks Rafał!
• 0.3.8 2019.04.16 Merge Pull Request #7. Thanks Alexander!
• 0.3.8.5 2019.04.21 Merge Pull Request #9. Thanks WO15!
• 0.3.9 2019.05.06 Revise the serial port selection logic. Support using PL011 uart on Raspberry Pi Model 3 and Zero W which is selected by setting dtoverlay=pi3-miniuart-bt or dtoverlay=pi3-disable-bt. Thanks 片岡さん for your kindly report including this issue!
• 0.4.1 2019.08.11 Add --serial_device option as solution of issue#12. Thanks Actpohomoc and TBR-BRD!
• 0.5.1 2020.05.16 Add --serial_console_untouched option to support execution without sudo asked as issue#17. Thanks ralphbe91!
• 0.5.2 2020.06.30 Update the link for datasheet of MH-Z19B from version 1.0 to version 1.5 based be pointed it out as issue#18. Thanks WO15!
• 0.6.1 2020.07.07 Add --detection_range_10000 option to support Set 0~10000ppm detection range asked as issue#19. Thanks WO15!
• 0.6.3 2020.08.27 Fix issue#21. Thanks idegre!
• 3.0.0 2021.02.05 PWM support.
• 3.0.1 2021.02.17 Fix a degradation of not running with python3. Thank you Masahiko OHKUBO san for your report.
• 3.0.2 2021.03.25 Fix to support RPi4 correctly as issue#29. Thanks iperniaf!
• 3.0.3 2021.11.08 Fix issue#35. Thanks false!
• 3.0.4 2011.11.11 Fix issue#36. Thanks David Bock
• 3.0.5 2022.01.01 Fix issue#38. Thanks kzehnter!
• 3.1.0 2022.01.22 add --co2valueonly option by merging issue#39 and issue#40. Thanks jonesthefox!
• 3.1.1 2022.01.23 remove code clone.