This tool reads the current radon level from the “Airthings Wave” radon detector without using the official smartphone app.
The official app cannot export radon levels to an external file. This tool allows you to create such a file.
Note: Don’t expect a finished product here. The tool and the README serve mainly as a way to document how to interface with the Wave.
A couple of days after publishing this, Airthings themselves made instructions and a script available at https://airthings.com/raspberry-pi/. Their script is written in Python 2 and does not report the “Other characteristics” (described below), but appears to have equivalent functionality otherwise.
It may be possible that the Wave must be connected to the official app at least once before you can use this program, so you will probably not get around registering an account with Airthings.
The radon level history stored on the Wave itself cannot be accessed with this program. To get around this, I run it continuously on a Raspberry Pi that connects regularly to the radon detector.
Make sure you install the latest firmware. The Wave and also this script were very unstable until I installed firmware from Feb. 21, 2018.
- An Airthings Wave
- A Bluetooth adapter that supports Bluetooth Low Energy (BLE).
You need:
- The bluez software
- Python 3
- The
bluepyPython library
The following will install the above on Debian/Ubuntu/Raspbian (it will install
the bluepy Python library into a virtualenv):
sudo apt install build-essential python3-venv python3-pip libglib2.0-dev bluez
python3 -m venv env
env/bin/pip install bluepy
After the above, scan for your Wave device with
sudo hcitool lescan
This should list the device addresses of all Bluetooth devices that are nearby. The Wave probably has a device address that starts with 98:07:2D.
It may be more comfortabe to use an app on your smartphone that can scan for Bluetooth Low Energy devices. It doesn’t matter as long as you find out what the device address is.
Finally, you can run the program:
env/bin/python radonwave.py ADDRESS
Replace ADDRESS with the device address that you found out above.
For MQTT support, please install the paho.mqtt package in the virtual environment:
env/bin/pip install paho.mqtt
To regularly post measurements to an MQTT server, I use a script named radonlog.sh:
env/bin/python radonwave.py --wait 0 --mqtt MQTT-SERVER-HOSTNAME --topic sensor/wave ADDRESS >> radonlog.txt
Make the script executable with chmod +x radonlog.sh.
Adjust MQTT-SERVER-HOSTNAME, sensor/wave and ADDRESS as necessary. If authentication is required,
add --username myusername and, if a password is required, also --password mypassword. To change the default port (1883), use --port PORT, where PORT is the port number.
Due to the --wait 0, this will only run once and exit. For regular measurements, I then use a cron job that runs twice an hour. I used to crontab -e to edit the crontab and added this line:
*/30 * * * * $HOME/radonlog.sh
This should be more reliable than running the script with --wait 1800, and the measurements will be at well-defined times.
- The nRF Connect app was very helpful. It allows to connect to the device via Bluetooth Low Energy (BLE) and browse the services that are available.
- GATT (part of Bluetooth) specifies some standard “characteristics”. The Wave offers the standard temperature and humidity characteristics. This is very easy to see in nRF Connect.
- Radon levels are reported in two different characteristics. Characteristics even come with proper descriptions, so this is also easy to spot from nRF Connect.
$ sudo gatttool -I -b YOUR-DEVICE-ADDRESS
[98:07:2D:xx:yy:zz][LE]> connect
Attempting to connect to 98:07:2D:xx:yy:zz
Connection successful
[98:07:2D:xx:yy:zz][LE]> char-read-uuid 00002a6e-0000-1000-8000-00805f9b34fb
handle: 0x0022 value: 1c 07
The two bytes 1c and 07 were returned. To convert to temperature, swap them (0x071c), convert to decimal (1820) and divide by 100: The temperature is 18.2°C.
It is similar for humidity:
char-read-uuid 00002a6f-0000-1000-8000-00805f9b34fb
handle: 0x0026 value: 68 10
The value 0x1068 was returned, which is 4200 in decimal. Divide by 100 to get 42% relative humidity.
There are two characteristics:
- “Radon conc. average” is available by reading the characteristic b42e0a4c-ade7-11e4-89d3-123b93f75cba.
- “Radon conc. 1 day” is available by reading the characteristic b42e01aa-ade7-11e4-89d3-123b93f75cba.
That is, you can read the values with char-read-uuid and using the above number.
Again, two bytes are returned that need to be swapped, but they must not be
divided by 100. The unit is Bq/m³.
“Radon conc. average” is identical to the value that the app reports as current radon level. This value is updated every 60 minutes. If you reset the Wave, a zero is reported during the first 60 minutes. It seems that measurements are actually even slower: When I moved the device from the basement to a place outside the house, it took 24 hours until the value reported here had dropped from over 500 to 17.
The meaning of the “Radon conc. 1 day” value is described by Airthings on their Raspberry Pi website as follows:
The radon long term measurements are averaged from the batteries are inserted up to one year.
It appears that after a reset, the value is identical to “Radon conc. average” for the first 24 hours and then starts to differ.
There is a characteristic called “Status info” available by reading from b42e1348-ade7-11e4-89d3-123b93f75cba. It is identical to the humidity characteristic except for once every 24 hours, when this one is 0, but the true “Humidity” characteristic still shows a sensible value.
A characteristic called “Accel. Light 5m” is available from b42e1096-ade7-11e4-89d3-123b93f75cba.
The second byte of this 16-bit value appears to be brightness, as @christianchristensen found out. See also the discussion in issue #1.
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The Wave also reports the current time as a Bluetooth characteristic. This is quite likely synchronized by the app.
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If your Bluetooth adapter seems not to work, you may need to unblock it:
sudo apt install rfkill sudo rfkill unblock bluetooth
