info

https://hackaday.com/2020/12/08/exploring-custom-firmware-on-xiaomi-thermometers/

https://github.com/atc1441/ATC_MiThermometer

https://github.com/pvvx/ATC_MiThermometer

 Xiaomi Smart LCD Screen Digital Thermometer 2 Mijia Bluetooth Temperature Humidity Sensor Moisture Meter Mijia App

https://www.aliexpress.com/item/1005002401046796.html

LYWSD03MMC

decode using gatttool

https://ndimension.design.blog/2021/12/16/reading-data-from-xiaomi-mi-temperature-and-humidity-monitor-2-lywsd03mmc/

root@rpi2:/home/pi# sudo hcitool lescan
LE Scan ...
A4:C1:38:D8:3F:9C ATC_D83F9C

open source firmware

https://github.com/bentolor/xiaomi-mijia-bluetooth-firmware

simple shell to send reading to influx

https://github.com/dpavlin/air-quality/blob/master/ble-mijia.sh

https://github.com/dpavlin/air-quality/blob/master/system/ble-mijia%40.service

https://www.youtube.com/watch?v=NXKzFG61lNs

Home Assistant

connected to home assistant using https://esphome.github.io/bluetooth-proxies/

get bindkey using https://atc1441.github.io/TelinkFlasher.html

https://esphome.io/components/sensor/xiaomi_ble.html?highlight=xiaomi_ble#obtaining-the-bindkey

[core-ssh ~]$ tail -18 config/.storage/core.config_entries
      {
        "entry_id": "574243c45c4485523ec174e18cfcf1ad",
        "version": 1,
        "domain": "xiaomi_ble",
        "title": "Temperature/Humidity Sensor DC63 (LYWSD03MMC)",
        "data": {
          "bindkey": "a6da0c1d99200efe9c9afb8fd9a534ef"
        },
        "options": {},
        "pref_disable_new_entities": false,
        "pref_disable_polling": false,
        "source": "bluetooth",
        "unique_id": "A4:C1:38:90:DC:63",
        "disabled_by": null
      }
    ]
  }

flash new firmware to sensor https://github.com/pvvx/ATC_MiThermometer

open in chrome on android to flash firmware,
change announcement to BTHome,
set time,
disconnect to start sending data to home assistant

flashing serial port

pinout

DTR - 3V3 (so that reset works)
GND - GND
TX - P14 - SWS

https://pvvx.github.io/ATC_MiThermometer/USBCOMFlashTx.html

https://github.com/pvvx/TlsrComSwireWriter

https://github.com/pvvx/ATC_MiThermometer?tab=readme-ov-file#the-usb-com-adapter-writes-the-firmware-in-explorer-web-version

reed switch

https://github.com/pvvx/ATC_MiThermometer?tab=readme-ov-file#reed-switch-or-button-functions

It is possible to solder a reed switch on the LYWSD03MMC board to the pins marked "P8" (GPIO PA6) and GND.