CO2MiniMon

This Linux program reads temperature and relative CO2 concentration data from a CO2Mini sensor and writes the values to temporary files. I use it to display the data in i3status.

Setup

Put the udev rules file in /etc/udev/rules.d/, then reload the rules with:

# udevadm control --reload-rules && udevadm trigger

Then, when you plug in the device, /dev/co2minix will be created as a symlink to the appropriate /dev/hidrawx.

Build and run:

$ ./build.sh
$ ./out/release/co2minimon

The 2 output files specified in the source code should be created and continually updated with the latest values.

Device Support

There are different versions of this device, frequently called the CO2Mini or the RAD-0301.

Some versions use a crappy encryption scheme as a detterent to getting the data out. For some wonderful and informative reading on this subject, see Reverse-Engineering a low-cost USB CO₂ monitor.

For whatever reason, my device doesn't seem to engage in these encryption shenanigans, so I can just get the data by decoding the very simple protocol.

My device has model number ZGm053UKA, and Linux reports the following data for it:

# lsusb --verbose -d 04d9:a052

Bus 001 Device 020: ID 04d9:a052 Holtek Semiconductor, Inc. USB-zyTemp
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               1.10
  bDeviceClass            0 
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0         8
  idVendor           0x04d9 Holtek Semiconductor, Inc.
  idProduct          0xa052 USB-zyTemp
  bcdDevice            2.00
  iManufacturer           1 Holtek
  iProduct                2 USB-zyTemp
  iSerial                 3 2.00
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x0022
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         3 Human Interface Device
      bInterfaceSubClass      0 
      bInterfaceProtocol      0 
      iInterface              0 
        HID Device Descriptor:
          bLength                 9
          bDescriptorType        33
          bcdHID               1.10
          bCountryCode            0 Not supported
          bNumDescriptors         1
          bDescriptorType        34 Report
          wDescriptorLength      53
         Report Descriptors: 
           ** UNAVAILABLE **
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0008  1x 8 bytes
        bInterval              10
Device Status:     0x0000
  (Bus Powered)