How to decode a 433Mhz RF signal (Arduino)

So you have a device which has a 433Mhz RF remote control and you would like to have an Arduino with a RF transmitter emulate the remote and control the device directly.
The first thing is to order a couple of parts that you will need. You will want a 433Mhz transmitter and receiver and you can get the ones advertised for the Arduino very cheaply off ebay. You will also need a prototype board and some jumper wires to temporarily connecting the RF receiver.
Next you will need a logic analyser so you can view the signal and decode it. I bought a 'USB Logic Analyser' from the ebay seller EllieShang. This logic analyser is programmable and there is a good guide that you should read about programming it to work with different software on jwandrews.co.uk. My logic analyser happened to already be set to work with the Salae Logic analyser software (can be freely downloaded) so I didn't need to reprogram it.

Now that you have all that you need connect the RF receiver to the prototype board. You can use the 5V and GND from the Arduino to power the RF receiver. You dont need to solder an additional antenna to the RF receiver as it will work fine if you just hold the transmitter remote control within a few cm. Connect the logic analyser to the GND and its first input to the RF receiver data pin and you are ready to go.


Now you should be able to hold the remote near the RF receiver, hold down a button and capture the waveform in the Saleae software. It should look something like this

Head over to Tinkerman's blog for instructions on how to decode the waveform. The only thing not mentioned there is how to calculate the pulse length. A 'short' is one pulse width wide and a 'long' is 3 pulse widths. So you can see that each of the four possible values are 8 pulse widths in length. There are twelve codes so that give 12*8=96. In addition there is also a synchronisation pulse at the end followed by 31 low pulse widths. So overall the transmission is 128 pulse widths. So you can calculate the pulse width as 39.24ms/128 = 307us. If you wish to make sure your Arduino is spot on with its timing you can just capture its signal and compare and tweak the timing as required.

To see how to program an Arduino with this data have a look at my blog entry Controlling Bye Bye Standby devices using an Arduino