Computing stuff tied to the physical world

OOK signaling with an RFM12B

In AVR, Software on Mar 3, 2009 at 00:01

Although the RFM12B was designed for FSK (frequency-shift keying), it can also be used for OOK (on-off keying) transmissions. The trick is simply to turn its transmitter on and off via the SPI interface.

This can be used to control simple RF-controlled devices such as the FS20 power control units by Conrad and ELV in Germany. Here’s a sketch which turns a remote device (lamp, etc) on and off:

OOK signaling with an RFM12B

It turns out that the 868 MHz version of the RFM12B can even transmit 433 MHz signals, at least for simple OOK. The following example turns a device on and off via the low-cost KlikAanKlikUit units sold in the Netherlands, using the same 868 MHz radio module as above:

OOK signaling with an RFM12B

Both demo’s have been added to the RF12 source code library. Other slow-rate bit-stream protocols similar to the above could easily be added.

No attempt has been made to receive OOK signals right now, though one could imagine reading out the RSSI bit to determine the presence of a carrier…

  1. Hello. I just stumbled upon this blog while searching for FS20. I found it very interesting because I like logging stuff and little gadgets, although I don’t have the knowledge to build anything myself.

    what I found most interesting though was the ability to control FS20 components. I have a few of those and would like a device that can issue macros and and listen in to the sensors, preferably without a computer. Is this something you have in mind?

    For my setup I would like to listen to light sensors and motion sensors in the FS20 series and depending on their state respond differently. For instance, if it is dark outside and the lights are off, if there is motion the lights should go on for a minute. Or if a window is opened the FHZ8v should turn off the heaters until the window is closed again. This might not be what you had in mind, but if it is I’d be happy to tell you more.

  2. I can see that you have several projects running so I can understand that it will take a while. I am not that concerned with the security since it is mosltly lightning that I am running.

    I will probably go with FS20 manager, but he is not yet there with conditional macros. It can also only control FS, FHT and HMS 100, nothing on the 433 MHz band, otherwise some Nexa support had been nice.

    If you haven’t already, you should probably check the FS20 Manager out, maybe you can get some ideas. He is very friendly and helpful.

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