MH-Z19 CO2 sensor reader, logger and visualiser
Python scripts to read, log and plot CO2 readings from an MH-Z19 sensor over UART.
MH-Z19 CO2 sensor reader, logger and visualiser
- Reads data from UART(serial)-connected MH-Z19 (or MH-Z14) sensor using python 3.
- If you dare to install nodejs you can visualise the logged data (using html and plotly.js library).
Repository: sammcj/CO2-Logger
Usage#
Note this post is from 2016, in 2021 I replaced my custom Co2 loggers with an Aranet4. While very expensive, is and excellent off-the-shelf solution, with many features.
Connection#
Sensor can be queried using 3.3v UART at 9600 bps. Sensor main feed voltage is 5v.
Can be connected to computer using almost any USB-UART converter if voltage matches.
Requirements#
- Python3
pip3 install serial pyserial- A USB -> Serial UART connector (Could also be used with Raspberry Pi, ESP8266, Arduino etc…)
- MH-Z19 Co2 Sensor (Around $25AUD on eBay)
Querying#
$ python3 CO2Reader.py --tty=/dev/tty.SLAB_USBtoUART --timeout=2
Connected to /dev/tty.SLAB_USBtoUART
2019-02-25 07:44:48 558 58
2019-02-25 07:44:49 558 58
2019-02-25 07:44:51 558 58
...
3 fields separated by tab: timestamp, CO2 concentration (ppm), internal sensor temperature (Celsius)
Use stream redirection to save data series to file:
touch co2.log
python3 CO2Reader.py --tty=/dev/tty.SLAB_USBtoUART --timeout=2 >>co2.log
Options#
--tty(optional) tty to connect to (default is/dev/tty.SLAB_USBtoUART)--single(optional) perform a single measurement and exit--quit(optional) connect to the sensor and quit immediately--timeout(optional) time between requests (defaults to10seconds)--command(optional) raw command to pass to the sensor - use carefully (default is to read Co2 levels)
Sensor Commands#
Raw commands can be passed to the Co2 sensor, these to be used with caution.
Example:
python3 CO2Reader.py --tty=/dev/tty.SLAB_USBtoUART --timeout=1 --command='0xff, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79'
Default operation (Reads Co2 levels)#
0xff, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79
Enable ABC#
0xFF, 0x01, 0x79, 0xA0, 0x00, 0x00, 0x00, 0x00, 0xE6
Disable ABC#
0xFF, 0x01, 0x79, 0x00, 0x00, 0x00, 0x00, 0x00, 0x86
Measurement Ranges#
(Note: Untested)
- 1000 =
0xFF, 0x01, 0x99, 0x00, 0x00, 0x00, 0x03, 0xE8, 0x7B - 2000 =
0xFF, 0x01, 0x99, 0x00, 0x00, 0x00, 0x07, 0xD0, 0x8F - 3000 =
0xFF, 0x01, 0x99, 0x00, 0x00, 0x00, 0x0B, 0xB8, 0xA3 - 5000 =
0xFF, 0x01, 0x99, 0x00, 0x00, 0x00, 0x13, 0x88, 0xCB
Run Zero Point (400ppm) calibration#
- Run this for 10mins + in 400ppm Environment
WARNING: DO NOT RUN THIS UNLESS YOU KNOW WHAT YOU ARE DOING!
0xFF, 0x01, 0x87, 0x00, 0x00, 0x00, 0x00, 0x00, 0x78
Visualizing#
- Install npm dependencies
npm install - Start server
python3 -m http.server 8088 --bind 127.0.0.1 - Open browser at http://127.0.0.1:8088/plot.html
- Select your log file in input field
Technical Specifications MH-Z19#
| Attribute | Value |
|---|---|
| Target gas | Carbon Dioxide CO2 |
| Operating Voltage | 3.6 to 5.5 Vdc |
| Operating current | < 18mA average |
| Interface levels | 3.3 Vdc |
| Output signal format | UART or PWM |
| Preheat time | 3 min |
| Response time | <60 s |
| Accuracy | ± (50 ppm+5% reading value) |
| Measuring range | 0 to 5000 ppm |
| Operating temperature range | 0 to + 50°C |
| Dimensions | 33mmx20mmx9mm(LxWxH) |
Wiring#
| Function | UART / Signal | MH-Z19 pin |
|---|---|---|
| Vcc +5V | +5V | 6 Vin |
| GND | GND | 7 GND |
| UART | TXD0 | 2 RXD |
| UART | RXD0 | 3 TXD |
Photos#
MH-Z19 Sensors#
Connected to a USB -> UART adapter#
Calibration#
Don’t use this function unless you know what you are doing or you may incorrectly calibrate the sensor!
(Australia has an average of around 400-410PPM and Sensor zero point is 400PPM)
Credits#
- Inspiration taken from my old AirQualityLogger project
- Thanks to @matmunn for Python 2->3 upgrade.
- Originally forked from https://github.com/alpacagh/MHZ14-CO2-Logger
Licence#
MIT licence