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.