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
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
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.
