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Showing posts from May, 2014

Messing with 433MHz equipment

We all know and love wireless devices. For example wireless doorbells. They seem so cool yet mysterious. How do they work?

Wireless doorbells:

They come with a receiver and the transmitter that you stick near your front door. Simple! They are wireless, so they use ISM bands. Most commonly the 433 MHz range. So when you press your door bell button the bell rings. The transmitter sends data out and the doorbell responds via sound – Simple!

DECODING

This is the first time when I used GNU Radio. I knew that these doorbells probably send data out with AM/OOK modulation. That was confirmed later on.

I made a quick GNURadio program to decode and record necessary signals.

I connected the rtl-sdr, pressed execute and started smashing the doorbell button. And what do you know, it works.

This was the output.



You can clearly see the repeating patterns.

Later on I created a different flow graph so could record these signals.





And then viewing them with Audacity.



I used Audacity because it works better when tr…