Over on Kickstarter we've recently come across a project called "WeatherSense" which is currently being crowdfunded. WeatherSense is a custom built set of 433 MHz wireless weather sensors made for makers. The outdoor "WeatherRack2" unit includes sensors and features like an anemometer, sunlight sensor, rain gauge, UV sensor, temperature and humidity sensor. wind direction sensor, as well as a solar panel for battery life extension and a Stevenson screen for shielding. They also have indoor units that measure temperature and humidity.
What's interesting to us is that they are using an RTL-SDR + Raspberry Pi as part of their 433 MHz receiver system. Their system includes a Raspberry Pi SD card image with built in Python software that is used with the RTL-SDR for receiving and decoding the weather sensor signals. They also provide an option for a simpler Arduino + 433 MHz receiver kit if you didn't want to use an SDR.
The campaign is currently fully funded, with 6 days left in the campaign. A kit including RTL-SDR and WeatherRack2 currently costs US$126 + shipping.
Over on YouTube user hubmartin has uploaded a video showing how to use an RTL-SDR and the Universal Radio Hacker (URH) software to reverse engineer and clone a 433 MHz remote control. URH is used to extract the signal timing and modulation characteristics as well as the binary/hex code.
Then in order to clone the signal hubmartin uses a cheap IoT microcontroller with button and 433 MHz transmitter attachments. Some C code is then used to program the microcontroller and 433 MHz transmitter with the extracted signal information and to transmit on a press of the button. In his example hubmartin uses his cloned dongle to control a wireless power plug and a motorized projector screen.
Universal Radio Hacker SDR Tutorial on 433 MHz radio plugs
Over on YouTube user Andreas Spiess has uploaded a video showing how to use an RTL-SDR to reverse engineer 433 MHz ISM band devices such as Internet of Things (IoT)/home automation sensors and actuators.
Andreas decided to do this because he has a 433 MHz remote controlled actuated outdoor awning which he wants to have automatically retract when the wind speed gets too high. To do this he wanted to use a wireless 433 MHz ISM band weather station with wind speed sensor. But unfortunately he discovered that it has a proprietary protocol that can't talk to his awning, which also has it's own proprietary protocol.
Andreas' solution is to use an RTL-SDR and Raspberry Pi running the rtl_433 decoder software to receive the weather station data. The rtl_433 software already contained a decoder for his weather station, so no further reverse engineering was required. The data is then converted into MQTT which is a common TCP/IP protocol for IoT devices. MQTT is then read by Node-RED which is a flowgraph based programming environment for IoT devices.
Next, unlike the weather station rtl_433 did not already have a decoder implemented for his awning. So Andreas had to reverse engineer the signal from scratch using the Universal Radio Hacker software. Using the reverse engineered signal information, Andreas then uses an ESP32 processor/WiFi chip and cheap 433 MHz transmitter to implement a clone of the awning's remote control signals. The ESP32 is programmed to understand the MQTT data sent from the Raspberry Pi via WiFi, so now the weather station can control the awning with a little bit of logic code in Node-RED.
How to Hack your 433 MHz Devices with a Raspberry and a RTL-SDR Dongle (Weather Station)
To reverse engineer the doorbell, Paul used GNU Radio with the Complex to Mag decoder block to receive and demodulate the ASK signal. Once demodulated he was able to visually see the binary modulated waveform, and manually obtain the serial bit stream. From there he went on to create a GNU Radio program that can automatically obtain the binary strings from the ASK waveform.
In order to replay the signal, Paul found that the simplest way was to use the hackrf_transfer program, which simply records a signal, and then replays it via the HackRF transmitter on demand. With this method Paul was able to ring his doorbell via the HackRF.
Paul also confirmed his SDR results with an Arduino and 433 MHz transceiver. He then took it a step further and used the Arduino to create a system that could automatically receive and replay signals at 433 MHz and 315 MHz.
The goal of Ilias’ project was to be able to use the RTL-SDR and MATLAB to uncover the details of a 433 MHz transmitter he bought on Ebay. He wanted to see if he could determine the protocol and recover the data before even looking at the transmitter’s library code.
To do this he first used SDR# to record the data sent at 433 MHz. Then by looking at the waveform in the Audacity audio editor he was able to determine that the signal was on-off-key (OOK) modulated and from this knowledge he was able to manually recover the binary string. Next he used MATLAB to create a program that can automatically decode the received OOK signal. His post goes into further detail about the signal processing steps he took in MATLAB.
Gough shows how he was able to receive and decode the data from an Aldi weather station device and a wireless doorbell transmitter. He also was able to modify the rtl_433 code slightly to produce a CSV log file of the temperatures that were received and decoded from the weather station.