lektor January & February 2021 27In the DIY community (at least in Europe where I’m living),
433.92 MHz will ring a bell. Many cheap wireless devices such as
garage door openers, weather sensors, and doorbells are using this
frequency. Moreover, the hardware to communicate with these
devices is equally cheap.
The disadvantage is that most of these devices use plain
unencrypted radio communication, and if they do use some sort
of security, it’s quite weak and/or some proprietary algorithm that
doesn’t inspire much confidence. But there are so many available
devices and they are so cheap, that you can’t ignore them. For
security reasons, I only use 433.92 MHz temperature sensors: I
have one of them in almost every room of my house, and outside
too. I wouldn’t trust 433.92 MHz devices for critical tasks.
In this chapter, I show you how you read measurements of these
wireless temperature sensors and how to relay them to your MQTT
broker for further integration in your home automation system.
Note: in this book, I’m talking about 433.92 MHz, but depending
on where you live you have to substitute this by another frequency.
For instance, in the Americas, the corresponding frequency is
915 MHz. Just make sure that you buy the correct devices for
your country.
433.92 MHz protocols
Devices that are using the 433.92 MHz frequency operate in the
unlicensed industrial, scientific, and medical (ISM) frequency
band. But the frequency is one thing, the protocol they’re using
is another one. There’s no standard protocol for this frequency.
This is no Z-Wave or Zigbee. However, many protocols of these
devices have been reverse engineered, and you can talk to them
as long as you have a transceiver for the frequency band around
433.92 MHz and the right software to decode and/or encode
the protocol.Some interesting devices are:
> temperature, humidity and weather sensors by Alecto, Cresta,
La Crosse, and Oregon Scientific;
> door/window sensors with Hall sensor;
> switches and dimmers by Energenie, KlikAanKlikUit and
LightwaveRF;
> doorbell chimes by Byron and Chacon.You can also find many even cheaper devices on AliExpress and
Banggood that support the same protocols. And there are even
small PCBs such as the STX882 transmitter that you can connect to
a microcontroller or an Arduino board to create your own wireless
sensor boards.Control Your Home
with Raspberry Pi
RPi snoops on 433.92 MHz
By Koen Vervloesem (Belgium)
This installment of Elektor Books
presents a chapter excerpted from Koen
Vervloesem’s book Control Your Home
with Raspberry Pi, which was recently
published by Elektor. Koen explains how
to turn your RPi into a powerful receiver
and decoder for most, if not all, remote
control and sensor signals you can pick up
at 433.92 MHz, one of the best-known and
widest-used ISM frequencies.
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