The type of radio signal that LightWaveRF and similar devices send is known as OOK (On/Off Keying). This is because they simply switch the signal on and off for periods of time, rather than using amplitude or frequency modulation.

There is an article at Jeelabs on how to do OOK with the RFM12.

I tried this with the LightWaveRF signal from the window switch, which says it operates at 868MHz. I had to add a resistor and wire to the FSK/DATA/nFSS pin on the RFM12B. I did not change the capacitor on the device, so the result I get are not likely to be reliable at short of long distances from the transmitter.

rfm12 001

I modified the code written by JGJ Veken to investigate the signal I get from the LightWaveRF window switch. The good news is that is does pick up a signal. However, the signal appears to consist of just one bit! When the window switch is opened I get a pulse of varying length, and then 5 seconds later I get a second pulse whose length is a bit more reliable and averages at about 800 microseconds. The window switch flashes its LED twice when it is opened.

I get a more or less identical signal from the window switch when it is closed. The LED flashes once in this case. Again there is another “bit” 5 seconds later. It fact the second signal is usually 5041 or 5111 milliseconds later.

There is just enough information here for me to detect the window being opened or closed, but I cannot distinguish between the cases. If I had more than one window switch, I would not be able to distinguish between them.

I was expecting to see a packet of about 8 bytes (as with the 434MHz devices), including a unique id for the transmitter. I guess it is there, but the method I am using does not show it.

Things to try next are changing the capacitor on the RFM12B and monitoring the signal with an oscilloscope or equivalent.

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5 Responses to OOK

  1. gsalerni says:

    hi. interesting findings. I didn’t realise the lightwaverf range used different frequencies for different products. Was under the impression that it was all 433mhz and using the same protocol. Do you have any info on which products use which frequency/protocol. Was thinking of buying into that product having worked with various HomeEasy kit till now but maybe I’ll skip lightwave and move straight to zwave. I bought a set of 433mhz jeelinks hoping to use them to send and receive HomeEasy OOK – didn’t read the documentation to reaslise they were FSK not ASK devices till afterwards – so can send HomeEasy but no receiving without the same surgery you did so interested to see how you get on with the range for receiving. best of luck

    • Geek Grandad says:

      It is the LightWaveRF heating products that use 868Mhz. This includes the radiator valve, thermostat, and window switch. The window switch is designed to switch off a radiator when the window is opened. There is another LightWaveRF window/door switch available at some shops, that has a different description and is slightly cheaper. I am wondering if that uses 433MHz. I will post more information when I have it.

      Z Wave devices are a lot more expensive than LightWaveRF. Do you know if anyone has worked out how to control them from Arduino?

      • gsalerni says:

        I’ve searched and I can’t find anyone who has succesfully controlled zwave from arduino. The protocol is very complicated so I think a direct RF solution is unlikely. More promising I think would be to use a Zwave USB dongle such as the Aeon Z-Stick which I see someone has integrated with from a Raspberry Pi which might suit you better given your setup? Have a look at http://thomasloughlin.com/z-wave-controller-setup-on-my-raspberry-pi/
        Still a lot of configuration to be done up front. I got a lone of a Z-Stick a little while back and the PC software for it I found pretty unreliable but I only had 1 day to play with it so could be user error!
        The main attraction for me in Zwave over Home EAsy, lightwave, X10Rf etc, etc. is the ability to read back the state of things like sockets as they use two way communication – also means you get an ACK back so you KNOW that a command has been received and actioned. But as you say – t or 3 times the price. It would almost be cheaper to buy a jeenode and relay board and make my own range 🙂

    • Geek Grandad says:

      Yes, I had a quick look and only found the Zstick. 2-way communication would be very nice, but I still don’t like the price and lack of hackability of Zwave. Doing our own design sounds interesting. I think I will investigate that, even though mains voltages scare me a little.

      • gsalerni says:

        snap. I bought some EDF IAMs and ecomanager after seeing Jack Kelly’s lib. See you have done much the same now as well. I didn’t get a nanode though so I’ve been struggling to get it to work with my Jeelink (I liked the idea of having the tiny USB stick Jeelink as my all in one arduino/RF receiver for the IAMs and the CurentCost meter clamp sender transmissions). It was a special order to get the 433MHz jeelink instead of the default 868Mhz but only cost an extra couple quid so worth it I figured. Just need to hack Jack’s nanode and edf code a bit to get it to dive the jeelink now.

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