I use the following sketch to test if the doorbell speaker reacts on the signal I found. It turned out that it works better when I adjusted the timings a little bit. That's why you won't find 520 microseconds, but 417 microseconds in line 29 of the code.

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Introduction

When I bought a wireless doorbell recently, the following idea came to mind: there are so many home appliances which make use of wireless radio (RF) signals, why not try to control them with my Arduino Uno? Besides a brand new doorbell, I also have a wireless weather station, wireless speakers, a remote power supply, a toy car and my car keys which send and receive those wireless signals. Wouldn't it be cool to connect them to the internet and control them this way?

The most practical thing to do would be to use the remote power sockets and use the Arduino to control a lamp in the living room. But this has already been done. I also wanted to to make it a little easier on myself, so I decided to use the doorbell (Grundig model QH-831A), which makes use of just one signal instead of several different on/off codes. It would also be fun to connect it to Twitter. "Why?", several people asked me, raising their eyebrows. "Because!", I replied.

In the next drawing you can see the things we will have to do.

• Detecting when someone pushes the doorbell button and using the Arduino to post a message to Twitter when this happens.
• Searching Twitter and when a specific hashtag is found, make the doorbell chime.

Requirements

• RF sender and receiver components. I bought these.
• Arduino board. I use an Arduino Uno, together with a breadboard and some wires.
• Arduino WiFi shield. I'm pretty sure that an ethernet shield would also work when you change the Arduino code slightly, but I don't have one, so I couldn't test it.
• To make the sniffer circuit mentioned in part 2:
  • 3,5 mm audio plug with 3 segments (3 wires in its cable).
  • A 10 KOhm resistor and a 39 KOhm resistor.
  • A twitter account just for this purpose. Mine is @ArduinoDeurbel.