EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: rastislav on December 29, 2015, 01:10:51 pm
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Hello,
I'm trying to find/do secure RF switch (long term battery life) along with RF -> RS232 gateway (It's going to connect to PLC and UART or Modbus/RTP or TCP are ok)
My idea was to replicate what EnOcean has (they offer batteryless switch :-+ ) and EnOcean to rs232 gateway. However it costs more coin I'm willing to spend.
http://shop.loxone.com/enen/enocean-switch.html (http://shop.loxone.com/enen/enocean-switch.html)
http://www.intelcontrols.com/STC65-RS485 (http://www.intelcontrols.com/STC65-RS485)
I've seen some ideas done using rf modules in free frequencies
http://www.romanblack.com/RF/cheapRFmodules.htm (http://www.romanblack.com/RF/cheapRFmodules.htm)
What I've seen is, that someone added fixed serial Id into transmitter which is sent when switch is pressed to receiver. However I don't see how security can be added to these and is probably the hardest thing to do correctly DYI (or am I wrong and some protocol exists?)
http://www.circuitstoday.com/remote-control-circuit-through-rf-without-microcontroller (http://www.circuitstoday.com/remote-control-circuit-through-rf-without-microcontroller)
On the example above, receiver would be tied to rs232 to provide different codes depending on button pressed instead of direct output control.
Range of 15m indoors and 20m outside is enough for me.
EDIT: found module only from enOcean for 31 pounds. Does some cheap enOcean -> rs232 or rs485 gateway exist? Or can be made? Haven't found protocol which is used there yet...
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I would recommend against trying to 'roll your own' security, it is much harder than it looks. Probably the best approach is the Z-wave or Z-wave-plus ecosystem, but it may be too expensive for you.
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LPRS ERIC modules mention encryption options in the datasheet:
http://www.lprs.co.uk/resource-centre/downloads/eric-software-datasheets/ (http://www.lprs.co.uk/resource-centre/downloads/eric-software-datasheets/)
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For RF remote control (one-way) the rolling code method is mostly used. There are dedicated chips for that, like in garage door openers.
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The first thing you have to do is define the security threats that matter to you. Only then can you start to define whether a particular solution is "secure".
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@bookaboo Thanks for showing LPRS ERIC modules. They indeed have AES, which can encrypt communication. It uses msp430 which is great since I'm familiar with them. Eavesdropping and replyattacks can be easily coped with these modules. With operation only during button presses I estimate Li-Ion batery (1 time use) can last quite a long time.
I'd say, having RF link to home automation using these modules has it's advantage of potentially being quite secure if implemented correctlyOnly disadvantage I see, that it can only be serviced by me :-\ . However it will not control anything critical, only add comfort to have switch a lot closer to bed :D (and it will do what it is programmed to do = security is a must)
@madires Yes, I was looking into garage openers as well, but haven't been successful with finding receiver with rs232 output, only fixed output contacts. That would save me lot of $ if such thing existed