This is intended to allow you to connect an MH-Z19B CO2 sensor to an M5 atom matrix to get a compact, simple network-enabled CO2 monitor.
You will need:
- M5 Atom Matrix
- MH-Z19B sensor (it may also work with the MH-Z19C, depending on the underlying software library)
- jumper wires
- soldering equipment, including heat-shrink tubing
The MH-Z19B datasheet shows the pins on the terminal wires which come with the sensor. I cut these wires then soldered them to jumper cables making it possible to plug the sensor into a breadboard - or the back of the M5 Atom Matrix.
Cut the wires from the cables which came with the sensor and connect them to jumper cables. In mine I wired red-red, black-black but had to change some colours so it goes green-blue and blue-yellow.
It should be possible to also connect these wires to a grove connector and so make it possible to plug into the grove connection in the base of the M5.
Plug red and black in to 5V and G on the back of the M5.
Plug blue and yellow into G22 and G19 on the back of the M5.
Connect the USB-C cable and upload the software.
Once the software is loaded onto the M5, you can then unplug the device and power it from a USB power source separate and away from the computer.
This code depends on the following libraries:
The Arduino IDE should prompt you to help install these libraries, or others which are also required.
The code is largely a mix of the M5Atom example code and the ErriezMHZ19B example code. Both of these are released under the MIT license and this license is applied to this work.
Having assembled the hardware and uploaded the compiled software to the M5, you will initially need to connect to the M5 on its own wifi network (SSID: M5STACK_SETUP) to provide it with wifi credentials for your wifi network. Once this is done, the M5 will reset and provide a website at http://co2monitor.local/
The website and the display will indicate "warming up" for the first three minutes of powered operation. After this they will display
- Web interface presents current CO2 concentration (averaged over readings for the past 5 minutes) and graphs of CO2 concentration.
- LED display indicates either warm up (the MH-Z19 takes three minutes to be ready to give readings) or the current CO2 concentration as scrolling digits.
- Raw CO2 readings can be downloaded in CSV format for analysis
Issues will be generated for these in GitHub and the list should get shorter.
- The software does not handle cppQueue properly and does not cleanly re-use the data. Behaviour beyond 24 hours of operation is not well-defined.
- Graphs are badly labelled in the time axis.
- Graphs should scale better
- Wifi set-up should better defined
- M5 should use accelerometer to detect "up" and orient the LED display accordingly