This is intended as a tutorial and utility for people who want to add a remote control to the Polyglot Node Server here:
This node server is for use with the ISY Home Automation controller.
This code is probably useful, at least as an example, for anyone trying to hack 315 MHz or 433 MHz remote controls that use simple OOK (on/off keying), or PDM (pulse density modulation) modulation.
PDM is effectively timed pairs of Transmitter-ON, Transmitter-OFF. The transmitter is turned on and emits a signal at the given frequency for a given time. After the given time the transmitter is turned off for a given time. Time for our purposes is specified in microseconds (us). Each pair of timed on/off transmission is a symbol. Multiple symbols are strung together to make up the dataset that is transmitted when a button is pressed on the remote control.
Within this repository is a (very simple) library that will read demodulated data in the form of a .wav file and convert that into a python data structure that can be used for emulating the remote control.
There is also a Python library class that will transmit the remote commands if a simple radio is connected up to a Raspberry Pi computer. The code is simple and could be ported if you so desire. An example of connecting a transmitter to a Raspberry Pi can be found here:
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Acquire an RTL-SDR radio (several versions available on Amazon for about $25).
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DETERMINE THE FREQUENCY OF YOUR REMOTE... I forgot this step in my initial check-in of this tutorial. There are two ways to do this... * The easy way or * The fun(?) way:
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The easy way: Search either the FCC site (difficult) or use google to search for the FCC ID which must be listed on the remote control. Usually FCC.IO (not official site) has a quick view including the frequency. FCC.gov has detailed information that you might spend some time looking through.
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The fun way: You must spend some time using one of several RTL-SDR tools to find the frequency of your remote control. A good, simple to install, package is SDRSharp which can be downloaded from AirSpy: SDRSharp Airspy makes SDR Hardware, but SDRSharp will work with most inexpensive radio dongles like the RTL-SDR.
Using the software watch the waterfall display to find the peak frequency where your remote transmits. You will likely need to scroll the frequency up and down to find this peak. The display shows about 2MHz of bandwidth max and the actual remote frequencies range by quite a bit. The 315 MHz band for remotes (FCC Part 15) is 285-322 MHz. For 433 the range is from 420 MHz to 450 MHz.
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Use Universal Radio Hacker to record the remote control buttons. Below is a sophomoric video that is a quick guide on how to record and demodulate each button then save to a .wav file: How-To Video
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Build a Python file similar to hbreeze_example.py here that specifies all of the information about your remote control including the ".wav" filename of each button you recorded.
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Run the Python file which will output a Python data structure. This data structure should be copied and pasted into a python program that will use it to playback the remote buttons on command.
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In your playback program import the file "txremote.py" and initialize the class PDMRemote with the data structure you saved above.
If you have a device that is at 315MHz or 433MHz then you can use the less expensive transmitters from Amazon (or eBay or Aliexpress)
315MHz Transmitter 433MHz Transmitter
If not... don't despair the TI CC1101 radio transceiver is actually a much better transmitter with better range and more flexibility. It can be set to transmit from 300 MHz all the way up to 928 MHz. The downside is that it uses 7 Raspberry Pi pins instead of 3. It is also a little bit more expensive.
Look around... you can find similar devices for varying prices.
If the radio you have does not have an antenna already soldered down (or if it is for the wrong frequency) then cut a length of wire and solder it into the hole or pad marked antenna. The wire length is important... use this formula to calculate the antenna wire length in inches:
length = 2808 / freq_mhz
For 315 MHz this would be: 2808/315 = 8.9 inches
Connect the CC1101 transmitter to the Raspberry Pi as shown below:
Connect the FS1000A transmitter to the Raspberry Pi as shown below:
