With this script you can read out the value of your LYWSD03MMC sensor, e.g. with Raspberry PI. Note Raspbery Pi 4 has a very limited bluetooth range. PI Zero W gives much longer range.
This sensor doesn't transmit its values in the advertisment data, like the LYWSDCGQ Bluetooth thermometer. This is more privacy friendly since no one can sniff your temperature readings. On the other side this means you have to establish a bluetooth connection with the device to get the data. When you're connected no other connection is accepted, meaning if you hold the connection no other can readout your temperature and humidity.
Once you're connected the LYWSD03MMC it advertises its values about every 6 seconds, so about 10 temperature/humidity readings per minute.
You need Python3 3.7 or above because of the dataclasses used in the Callback Function. If you don't have Python 3.7 please take the previous version from here https://raw.githubusercontent.com/JsBergbau/MiTemperature2/5d7b215d7b22d4c21d9244f8a4102513b928f2c7/LYWSD03MMC.py This version is a bit behind and connection error handling has a bug. If you really need this script, please open and issue and I'll post a new bugfree version.
For example Raspbian Stretch has only Python 3.5.3. If you like to upgrade your Distribution to current Buster release follow this Tutorial https://pimylifeup.com/upgrade-raspbian-stretch-to-raspbian-buster/ If doing so: Omit the rpi-update step.
If you like installing/compiling Python3.7 please take a look at this tutorial https://gist.github.com/SeppPenner/6a5a30ebc8f79936fa136c524417761d However it took about 5 hours to compile/run the regressiontests on a Raspberry PI3B. I use this compiled version directly without install. If you do, too, you have to change the first line in the script, pointing to your compiled Python version. For bluepy you can copy the bluepy-folder from home/pi/.local/lib/python3.7/site-packages/bluepy to Python-3.7.4/Lib and do a chmod +x bluepy-helper in Python-3.7.4/Lib/bluepy
Prequisites: python3 bluez python3-pip bluepy install via
sudo apt install python3 bluez python3-pip
pip3 install bluepy
usage: LYWSD03MMC.py [-h] [--device AA:BB:CC:DD:EE:FF] [--battery N]
[--count N] [--round] [--debounce] [--offset OFFSET]
[--TwoPointCalibration] [--calpoint1 CALPOINT1]
[--offset1 OFFSET1] [--calpoint2 CALPOINT2]
[--offset2 OFFSET2] [--callback CALLBACK] [--name NAME]
[--skipidentical N]
optional arguments:
-h, --help show this help message and exit
--device AA:BB:CC:DD:EE:FF, -d AA:BB:CC:DD:EE:FF
Set the device MAC-Address in format AA:BB:CC:DD:EE:FF
--battery N, -b N Read batterylevel every Nth update
--count N, -c N Read/Receive N measurements and then exit script
Rounding and debouncing:
--round, -r Round temperature to one decimal place
--debounce, -deb Enable this option to get more stable temperature
values, requires -r option
Offset calibration mode:
--offset OFFSET, -o OFFSET
Enter an offset to the reported humidity value
2 Point Calibration:
--TwoPointCalibration, -2p
Use complex calibration mode. All arguments below are
required
--calpoint1 CALPOINT1, -p1 CALPOINT1
Enter the first calibration point
--offset1 OFFSET1, -o1 OFFSET1
Enter the offset for the first calibration point
--calpoint2 CALPOINT2, -p2 CALPOINT2
Enter the second calibration point
--offset2 OFFSET2, -o2 OFFSET2
Enter the offset for the second calibration point
Callback related functions:
--callback CALLBACK, -call CALLBACK
Pass the path to a program/script that will be called
on each new measurement
--name NAME, -n NAME Give this sensor a name reported to the callback
script
--skipidentical N, -skip N
N consecutive identical measurements won't be reported
to callbackfunction
Note: When using rounding option you could see 0.1 degress more in the script output than shown on the display. Obviously the LYWSD03MMC just trancates the second decimal place.
In order to save power: It is recommended to read the battery level quite seldom. When using the --battery option Battery-Level is always read on the first run.
The --count option is intended to save even more power. So far it is not proven, that only connecting at some interval will actually save power. See this discussion JsBergbau#3 (comment)
Use sudo hcitool lescan --duplicate to get the MAC of your Sensor.
This sensor only sends its measurements only via notifications. There are quite often notifications because the temperature is measured with a precision of 2 decimal places, but only one shown on the display (and this value is truncated, see above). Trying to directly read/poll the characteristics returns always zeroes.
The temperature values often change between the same values. To get cleaner temperature curves a debouncing function has been implemented. See here JsBergbau#2 for more info.
When looking at the specifications this LYWSD03MMC Sensor is specified from 0 °C to 60 °C. The LYWSDCGQ (the Bluetooth Temperatur sensor with the round display and an AAA battery) is specified from -9.9. I can confirm this sensor also goes down to -9.9 °C. At colder temperatures it only shows an "L". But the correct data is still sent! So you even could use ist to watch the temperature in your freezer. However batterylife may be significantly reduced at those low temperatures.
./LYWSD03MMC.py -d AA:BB:CC:DD:EE:FF -r -b 5
Trying to connect to AA:BB:CC:DD:EE:FF
Waiting...
Temperature: 20.1
Humidity: 77
Battery-Level: 99
Temperature: 20.1
Humidity: 77
Temperature: 20.1
Humidity: 77
Temperature: 20.1
Humidity: 77
Temperature: 20.1
Humidity: 77
Temperature: 20.1
Humidity: 77
Battery-Level: 99
If you like gatttool you can use it, too. However it didn't notice when BT connection was lost, while this Python-Script automatically reestablishes the connection.
gatttool -I
connect AA:BB:CC:DD:EE:FF
#enable notifications
char-write-req 0x0038 0100
#Read battery-Level, consider: note value is in Hex format
char-read-hnd 0x001b
Strictly speaking enabling notifications every time is not necessary since the device remembers it between connects. However to make it always work, the Python-Script enables them upon every connection establishment.
Notification format
Notification handle = 0x0036 value: f8 07 4a d6 0b
f8 07 is the temperature as signed INT16 in little endian format. Divide it by 100 to get the temperature in degree Celsius
4a is the humidity. Only integer output :(
d6 and 0b are unknown to me. Tell me if you know what these values mean.
Sometimes script fails to connect and tries to connect forever.
Just exec killall bluepy-helper You can even do this while script is running. It will disconnect, but recovery automatically.
Since version 1.1 there is a watchdog-Thread checking when connection is lost for at least 60 seconds and then killing the corresponding bluepy-helper, so that other connections aren't affected. This is a workaround for an obvious bug in bluepy. This bug only occured so far when trying to (re)connect. Then this call to bluepy blocks sometimes forever.
If that doesn't help, a problem with the bluetooth stack could be the cause. To resolve:
sudo hciconfig hci0 down
sudo hciconfig hci0 up
Especially humidity value is often not very accurate. You get better results if you calibrate against a known humidity. This can be done very easy with common salt (NaCl). Make a saturated solution and put it together with the Xiaomi Bluetooth thermometer in an airtight box. Ensure that no (salt) water gets in contact with the device. Saltwater is very corrosive. Wait about 24 hours with a constant temperature. You should now have about 75 % relative humidity. I don't know how long it takes for the sensors to drift. So I will redo this procedure about every year.
E.g. mine shows 79 % RH when actually there is 75 %. Excecute the script with -o -4 to substract 4 from the readout value.
The offset is not linear over the whole humidity values. So you should calibrate at another point. MagnesiumChloride is recommended giving about 33% RH at 20 °C. Also Calciumchloride is suitable, but the humidity depends more on temperature. Be sure to have 20 °C. https://www.salzwiki.de/index.php/Deliqueszenzfeuchte
My Xiaomi Bluetooth thermometer shows 39% RH at 33% RH. So wie here have an offset of 6. Another hygrometer show 69 % at 75% RH and 33% RH at 33% RH. So offset +6 at 75% TH and offset 0 at 33% RH. Example for the Xiaomi to use 2 point calibration: At 75% RH you have to substract 4 from the readout value, at 33% RH you have to substract 6.
-2p -p2 75 -o2 -4 -p1 33 -o1 -6
-2p: Enables 2 point calibration
-p2 75: Point 2 at 75% RH
-o2 -4: Offset -4 at Point 2
-p1 33: Point 2 at 33% RH
-o1 -6: Offset -6 at Point 2
Note the values in between are interpolated linear and the result is rounded to the nearest whole number. It makes no sense to give floatingpoint number when the input is none.
Output example:
./LYWSD03MMC.py -d AA:BB:CC:DD:EE:FF -2p -p2 75 -o2 -4 -p1 33 -o1 -6
Trying to connect to AA:BB:CC:DD:EE:FF
Waiting...
Temperature: 20.83
Humidity: 39
Calibrated humidity: 33
Temperature: 20.82
Humidity: 39
Calibrated humidity: 33
Via the --call option a script can be passed to sent the data to.
Example
./LYWSD03MMC.py -d AA:BB:CC:DD:EE:FF -2p -p2 75 -o2 -4 -p1 33 -o1 -6 -b 5 --name MySensor --callback sendData.sh
If you don't give the sensor a name, the MAC-Address is used. The callback script must be within the same folder as this script.
The values outputted depends on the options like calibration or battery. So the format is printed in the first argument.
Example callback
#!/bin/bash
echo $@ >> data.txt
Gives in data.txt sensorname,temperature,humidity,humidityCalibrated,batteryLevel,timestamp MySensor 20.19 39 33 99 1578485287
Whereas the timestamp is in the Unix timestamp format in UTC (seconds since 1.1.1970 00:00).
There is an option not to report identical data to the callback. To distinguish between a failure and constantly the same values have been read, the option takes the number after which identical measurements the data is reportet to the callback. Use the --skipidentical N for this. E.g. --skipidentical 1 means 1 identical measurement is skipped, so only every second identical measurement is reportet to callback. I recommend numbers between 10 and 50, giving at least every minute respectively 5 minutes a call to the callback script (With 10 and 50 the actual time is slightly higher than 1 respectively 5 minutes). It is recommended to use the --round and --debounce option, otherwise there is a lot of noise with changing the temperature. See JsBergbau#2
Because of the implementation batterylevel is read after the first data received from sensor. This means after startup the first batteryvalue reported is always zero. After the second temperature reading the correct batterie value is passed to the callback function and updated via the --battery Option
All data received from the sensor is stored in a list and transmitted sequentially. This means if your backend like influxdb is not reachable when a new measurement is received, it will be tried again later (currently waiting 5 seconds before the next try). Thus no data is lost when your storage engine has some trouble. There is no upper limit (the only limit should be the RAM). Keep this in mind when specifing a wrong backend.
"sendToInflux.sh" is an example script for sending the data to influxdb via http-API. Precision was set to the level of seconds. This gives better compression ratios in influxdb.