There are some cheap Xiaomi Mijia thermometers out there.
What's interesting about them is that they can send their
measurements by bluetooth (eg to a mobile)
What's even more fun is that custom firmware can be upload
to them!
I'm using the PVVX firmware
https://github.com/pvvx/ATC_MiThermometer
This will broadcast the data as part of the ble announcements
so any bluetooth receiver can passively listen and receive the
data. It allows you to have many of these devices and efficiently
collect data without having to connect to each one individually.
---
This program acts as a receiver and posts the data to an MQTT server
as a JSON string, which can then be received by tools such as Home
Assistant.
Note the PVVX firmware can broadcast in different formats. I have it
configured for "custom"
The MQTT topic will be "atc/" followed by the device mac address
(eg "atc/123456789abc")
The JSON format is
{
"time": 1635948316,
"mac": "123456789abc",
"name": "ATC_789abc",
"tempC": 20.9,
"tempF": 69.6,
"humidity": 39,
"battMV": 2967,
"battpct": 85
}
Note: the name field may start as "" if sensor data arrives before the
device broadcasts its name (which can be set from the pvvx flashing tool)
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Needs the bluepy module and the paho-mqtt module
This may need to be run as root, or else capabilities can be set on the
bluepy-helper program
e.g
sudo setcap 'cap_net_raw,cap_net_admin+eip' ~/.local/lib/python2.7/site-packages/bluepy/bluepy-helper
With capabilities set then python applications can manage the bluetooth
stack without needing to be root.
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(c) Stephen Harris, Nov 2021
MIT licensed. See LICENSE file