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Read CO2 concentration from mh-z19 sensor on the Raspberry Pi & handle it. Detect Raspberry Pi model automatically and read value from appropriate serial device.
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README.md

mh-z19

Read CO2 concentration from mh-z19 sensor and handle it.

MH-Z19

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.

Cabling

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+--+---+------+---------+-----+-----+

Install & Setup

Full Set Install

Full Set include followings:

  • Setup script: Install & Setup following useful stuffs as:
    • mh-z19: A python module to read mh-z19 sensor.
    • PondSlider: A multipurpose versatile sensor handler for python, which read mh-z19 value and handle it.
    • autostart.sh: Utility making mh-z19 as system service to act periodically.

Install Full Set, download from release

or

git clone https://github.com/UedaTakeyuki/mh-z19.git

Then, got to the folder and issue setup.sh*

./setup.sh 

Necessary settings including serial port enabling are taken place in this script.

Install only sensor module

pip install pip install mh-z19

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. Also, please refer PyPi top page for detail.

read CO2 Sensor value

pi@raspberrypi:~ $ sudo python -m mh_z19 
{'co2': 668}

As above, sudo might be necessary because mh-z19 sensor value is read through serial connection and it request root permission in general.

Handle sensor value by PondSlider multipurpose sensor handler.

The installed mh-z19 module is correspond the pondslider which is multiple & versatile sensor handler to save, send and to do other necessary something with the sensor value.

As an example, we introduce following use case:

  • How to save sensor value to SD card as .CSV file.
  • How to send sensor value to free Remote Monitoring Service.

A brief explanation of pondslider

The pondslider read sensorvalue by sensor-handler specified, and pass the values to value-handlers* which do something with it.

PondSlider

Both sensor and value handlers are python module. For more detail of handlers, please refer this.

How to use sensor value to send to server, save to strage, and so on.

This module correspond the pondslider which is multiple & versatile sensor handler to save, send and to do other necessary something with the sensor value.

In case you choiced Full Install mentioned above, in other words, you've done setup.sh, the pondslider and there example handler's are already installed & setup.

How to save CO2 value on a SD card as a .CSV file.

You can do it with save2strage value handler which is in handlers/value/saver/save2strage, and configuration file to read from mh-z19 sensor and save by save2strage is prepared as config.save.toml on the mh-z19 installed folder.

On the mh-z19 folder By calling pondslider as follows;

sudo python -m pondslider --config config.save.toml

Then, /home/pi/DATA/co2.csv should be created and new line will be added for each call.

How to send CO2 Value to the MONITOR™ Service

The MONITOR™ is a free Remote Monitoring Service to show latest data on the web.

Please refer an introduction to grasp birds-eye understanding about MONIOR™.

A free account is available as follow. Then, login and get a view_id, which is unique id to point a data area on the MONITOR™ to show latest value and chart, as follow.

After get a value_id at your browser, return back to terminal of your Raspberry Pi, then you should set your this software to send measured value to the value_id. To do this, call setid.sh command in the mh_z19 installed directory. Let's say your value_id is vpgpargj, issue setid.sh command as follows:

./setid.sh vpgpargj

Then, call "pondslider" python script as follows:

pi@raspberrypi:~/mh-z19 $ sudo python -m pondslider
{'co2': 742}
co2
{"ok":false,"reason":"ViewID not valid"}

Your time-series chart on the MONITOR™ display on the browser must be updated by the latest CO2 concentration value.

How to set your Raspberry Pi to send CO2 data to MONITOR™ at 5 minute interval.

You can set it by autostart.sh command in the mh_z19 installed directory as follows:

./autostart.sh --on

You can tTurn off this as follows:

./autostart.sh --off

Also, You can check current status as follows:

./autostart.sh --status

For more detail, please refer this blog.

How to send CO2 Value to the ATT M2X.

The Pondslider also support ATT M2X. For detail, please refer this document.

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}
>>> 

Despite, I think the TT value might NOT be related to the ambient temperature, but also this might be a internal thermal sensor value which is pair with a infrared heater they are necessary for measuring CO2 concentration by NDIR (Non-dispersive Infrared) method.

So, returned temperature value might be not match with real temperature. Please refer detail about my argument as Is the undocumented TT value on the responses of command 0x86 really related to the ambient temperature?.

Q&A

Any questions, suggestions, reports are welcome! Please make issue without hesitation!

Blog

References

history

  • 0.1.0 2018.09.13 first version self-forked from slider.
  • 0.2.2 2018.11.19 introduce pondslider and separate this PyPi package.
  • 2.0.0 2019.01.18 Add Calibration, ABC on/off requested by this issue. Please refer this wiki.
  • 0.3.5 2019.01.22 Both Python2 & Python3 support
  • 2.3.6 2019.01.22 Merge Pull Request #3 & Pull Request #4. Thanks David!
  • 2.3.7 2019.02.25 Add --all option which requested as issue#5, thanks Rafał!
  • 2.3.8 2019.04.16 Merge Pull Request #7. Thanks Alexander!
  • 2.3.8.1 2019.04.20 Merge Pull Request #8. Thanks WO15!
  • 2.3.8.5 2019.04.21 Merge Pull Request #9. Thanks WO15!
  • 2.3.8.6 2019.04.22 Merge Pull Request #10. Thanks WO15!
  • 2.3.9 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!
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