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Mijia temperature/humidity monitor

Intro

This is a simple temperature + humidity sensor (amazingly called "humiture" by the OEM) with a LCD (and there seems to have an e-ink variant) screen.

The device seems actually that simple, it has the nordic DFU protocol, it send it's data via advertisement, and it has some debug services/char, that's it.

Services and characteristics

  • Generic Access (uuid=00001800-0000-1000-8000-00805f9b34fb)
    • Device Name (uuid=00002a00-0000-1000-8000-00805f9b34fb), props=READ WRITE handle=3
    • Appearance (uuid=00002a01-0000-1000-8000-00805f9b34fb), props=READ handle=5
    • Peripheral Preferred Connection Parameters (uuid=00002a04-0000-1000-8000-00805f9b34fb), props=READ handle=7
  • Generic Attribute (uuid=00001801-0000-1000-8000-00805f9b34fb)
    • Service Changed (uuid=00002a05-0000-1000-8000-00805f9b34fb), props=INDICATE handle=10
  • Message Service (uuid=226c0000-6476-4566-7562-66734470666d)
    • Humiture (uuid=226caa55-6476-4566-7562-66734470666d), props=NOTIFY handle=14
    • Message (uuid=226cbb55-6476-4566-7562-66734470666d), props=WRITE NOTIFY handle=19
  • Battery Service (uuid=0000180f-0000-1000-8000-00805f9b34fb)
    • Battery Level (uuid=00002a19-0000-1000-8000-00805f9b34fb), props=READ NOTIFY handle=24
  • Device Information (uuid=0000180a-0000-1000-8000-00805f9b34fb)
    • Manufacturer Name (uuid=00002a29-0000-1000-8000-00805f9b34fb), props=READ handle=28
    • Model Number (uuid=00002a24-0000-1000-8000-00805f9b34fb), props=READ handle=30
    • Serial Number (uuid=00002a25-0000-1000-8000-00805f9b34fb), props=READ handle=32
    • Hardware Revision (uuid=00002a27-0000-1000-8000-00805f9b34fb), props=READ handle=34
    • Firmware Revision (uuid=00002a26-0000-1000-8000-00805f9b34fb), props=READ handle=36
  • Nordic DFU (uuid=00001530-1212-efde-1523-785feabcd123)
    • DFU Packet (uuid=00001532-1212-efde-1523-785feabcd123), props=WRITE NO RESPONSE handle=39
    • DFU Control point (uuid=00001531-1212-efde-1523-785feabcd123), props=WRITE NOTIFY handle=41
    • DFU Version (uuid=00001534-1212-efde-1523-785feabcd123), props=READ handle=44
  • Mi Service (uuid=0000fe95-0000-1000-8000-00805f9b34fb)
    • Token characteristic (uuid=00000001-0000-1000-8000-00805f9b34fb), props=WRITE NOTIFY handle=47
    • Custom characteristic (uuid=00000002-0000-1000-8000-00805f9b34fb), props=READ handle=50
    • Firmware version characteristic (uuid=00000004-0000-1000-8000-00805f9b34fb), props=READ handle=52
    • Event characteristic (uuid=00000010-0000-1000-8000-00805f9b34fb), props=WRITE handle=54
    • Serial number characteristic (uuid=00000013-0000-1000-8000-00805f9b34fb), props=READ WRITE handle=56
    • Beacon key characteristic (uuid=00000014-0000-1000-8000-00805f9b34fb), props=READ WRITE handle=58

Message service

That's the only custom service (beside the DFU and the MI service, but these aren't specific to this device), it seems to be used only in the debug activity

Humiture characteristic

Humiture = Humidity + Temperature, this isn't from me, it's from the OEM. You can subscibe to it's notifications (real time data) and the data is as such:

  • parse = ParseValueUtil.parseHumitureValue(datainhexstring)

  • temp = parse[0] # float

  • humidity = parse[1] # float

  • if parse[2] == 0.0f # which should always be the case?!?

    • text = "unknown"

  • if parse[2] != 1.0f and parse[2] != -1.0f

    • text = "near"

  • parseHumitureValue(String str):

    • match = Pattern.compile("\w=(-?\d*\.?\d*)\s\w=(\d*\.?\d*)").matcher(str)
    • temp = match[1]
    • humidity = match[2] => data = w(?)='-'?(int)'.'?(int)(space)w(?)=(int)'.'?(int) => data = [a-zA-Z_0-9]=(-?[0-9]+.?[0-9]+)[[:space:]][a-zA-Z_0-9]=([0-9]+.?[0-9]+)

Message characteristic

  • if clicked on "Restart", send 43470006
  • if clicked on "screentest send 4347000104
  • if clicked on "screentestend" send 4347000105
  • You can subscribe to notifications, data:
    • if data.startswith('4347'):
      • if data[4-8] = '0002':
        • substr = data[8-10]
        • if substr != '00' and substr != '01':
          • display substr1

Broadcast data

The temperature sensor mainly work with broadcast data

It first check if the data starts with '95fe5020', and if the "type" is either 0d10 or 0a10

  • If it's 0d10, it parses the humidity and temperature from it

  • If it's 0a10, it simply return the bytes after it's size (it's the battery percentage)

  • if (str.indexOf("95FE5020") == 10):

    • if (str.indexOf("0D10") == 36):
      • return parseHexTemperatureHumidity(str.substring(42, (Integer.parseInt(str.substring(40, 42), 16) * 2) + 42));
    • if (str.indexOf("0A10") == 36):
      • return new float[]{(float) Integer.parseInt(str.substring(42, 44), 16)};

parseHexTemperatureHumidity(String str):

  • if ("56046F".equals(str) || "56045604".equals(str)):
    • return new float[]{99999.0f, 99999.0f}