Elektor_Mag_-_January-February_2021

30 January & February 2021 http://www.elektormagazine.com

With the example configuration file, rtl_433 now shows the output

of each sensor as a JSON dictionary (Figure 5). This is already a big

step forward to integrate your 433.92 MHz sensors into your home

automation setup, but the final step is to publish these values to

your MQTT broker.

Publishing 433.92 MHz sensor values to MQTT

The rtl_433 program has already support for sending the sensor

values it receives to an MQTT broker. Open the configuration file

(/home/pi/containers/rtl433tomqtt/rtl_433.conf) and find the line

that says:

output json

You can keep this line here because you can specify multiple

outputs, or change it to output kv if you prefer the default more

human-friendly output. Add the following line to define an MQTT

output:

output mqtt://mosquitto:1883,user=home,pass=PASSWORD

Make sure to enter the correct username and password for your

MQTT broker.

Warning: The rtl_433 program doesn’t support MQTT over TLS. If

you’re running the rtl_433toMQTT container on the same Raspberry

Pi as your mosquitto container, it’s no problem that they communi-

cate unencrypted: they’re on the same machine anyway. If you have

your RTL-SDR receiver on another machine than your MQTT broker

(for instance because you have better coverage there), I recom-

mend you run a mosquitto container aside from the rtl_433toMQTT

container and configure it as a bridge to your main MQTT broker

over an encrypted connection. See the appendix at the end of this

book for the details.

After a restart of your container, you should see an MQTT message

published under the rtl_433 main topic for each sensor value. You

can view this with:

mosquitto_sub -t ’rtl_433/#’ -v

For instance, every time the temperature and humidity sensor in

my freezer transmits a message, I see data like in Figure 6.

Now, you can still tweak a couple of things from the MQTT config-

uration. Consult the comments in the example configuration file

for the details. For instance, this configuration changes the MQTT

topics to something shorter:

output

mqtt://mosquitto:1883,user=home,pass=PASSWORD,device

s=rtl433/[model]/ [channel]/[id]

And if you’re not interested in the low-level metadata about the

radio connection, such as modulation, frequency, RSSI (received

signal strength indicator), SNR (signal-to-noise ratio) and noise,

just remove or comment out the report_meta level line in the

configuration file.

ration, which was fine for testing but didn’t use MQTT. Now let’s copy
an example configuration file to a path where rtl_433 is searching:

docker cp rtl433tomqtt:/usr/local/etc/rtl_433/
rtl_433.example.conf /home/pi/containers/
rtl433tomqtt/rtl_433.conf

Because I have mapped the directory containers/rtl433tomqtt in
your pi user’s home directory to /home/user/.config/rtl_433 in the
container, you can now edit this configuration file and restart the
container to use this configuration. For instance, you can disable
protocols you don’t need, or enable protocols that are disabled
by default.

The configuration file is heavily commented, which should help
you figure out what to change. Moreover, you can find a lot of
information in rtl_433’s online documentation (https://triq.org/
rtl_433/), including steps to add support for a sensor that is not
(yet) supported.

After the changes to your configuration file, restart the container:

docker restart rtl433tomqtt

If all goes well, the logs should show that rtl_433 stops searching
for a configuration file after the second file and finds it:

Reading conf from "/home/user/.config/rtl_433/
rtl_433.conf".

Figure 6: The rtl_433 command can send the received sensor values to your
MQTT broker.

Figure 5: The rtl_433 command can show the sensor values in many
formats, including JSON.