lektor January & February 2021 29

Search in this list for a line like this:

Bus 001 Device 008: ID 0bda:2838 Realtek

Semiconductor Corp. RTL2838 DVB-T

Note the bus and device number: 001 and 008. Now look at the

device files for the bus 001:

ls -l /dev/bus/usb/001

You should see a line like this:

crw-rw---- 1 pi root 189, 10 May 7 20:22 008

This shows that the device is owned by the user pi, which has read

and write permissions.

After this, create the container with:

docker-compose up -d

After the container has been created, look at its logs:

docker logs -f rtl433tomqtt

As shown in Figure 4, you should see some messages that the

rtl_433 program is trying to find a configuration file in a few places,

that is has registered more than 120 decoding protocols, and that

is has found a receiver device. Then you should see a message

‘Tuned to 433.920MHz’ and if all goes well you should now see

sensor values coming in. Have some patience, because many of

these sensors only transmit once a minute.

Configuring rtl_433

In the beginning of the logs, you saw that rtl_433 tried to find some

configuration files. It didn’t find one, so it just used a default configu-

Any Realtek RTL2832 based DVB dongle should work with rtl_433,
including the official RTL-SDR dongle. I’m using the RTL-SDR
dongle with a dipole antenna from the RTL-SDR antenna kit. Just
connect the antenna to the RTL-SDR and put the RTL-SDR in a USB
port of your Raspberry Pi.

Warning: The RTL-SDR produces quite a lot heat while it’s running.
Take care of where you position it.

Installing rtl_433toMQTT
The rtl_433 program is actively developed and maintained and has
more than 150 protocol decoders for various devices that trans-
mit on 433.92 MHz. Moreover, it can send the received values to
an MQTT broker. Luckily, someone created a Docker container
with rtl_433 for this exact purpose (https://github.com/bademux/
rtl_433toMQTT) [3].

First, create a directory for the container:

mkdir -p /home/pi/containers/rtl433tomqtt

Then add the container definition to your docker-compose.yml file:

version: ‘3.7’

services:
mosquitto:

mosquitto config

rtl433tomqtt:
image: bademux/rtl_433tomqtt:latest
container_name: rtl433tomqtt
restart: always
volumes:

• ./containers/rtl433tomqtt:/home/user/.config/
  rtl_433:ro


• /etc/localtime:/etc/localtime:ro
  devices:


• /dev/bus/usb:/dev/bus/usb

Enter the configuration of the Docker container for Mosquitto
instead of ‘#mosquitto config’. The container needs access to
the USB bus to read from the RTL-SDR device. Note also that the
directory you created is mounted as a volume. You don’t have to
create a configuration file yet.

First create a udev rule to give the right permissions to the USB
device:

sudo nano /etc/udev/rules.d/20.rtl-sdr.rules

Enter the following line:

SUBSYSTEM=="usb", ATTRS{idVendor}=="0bda", ATTRS{idPr
oduct}=="2838",OWNER="pi", MODE="0660"

Save the file with Ctrl+o and exit nano with Ctrl+x. Then unplug
the RTL-SDR and reattach it. Now look at the list of attached USB
devices:

lsusb

Figure 4: The rtl_433 command automatically finds the RTL-SDR receiver

and starts showing received sensor readings.