
Linux Light Bulbs: Enabling Internet Connectivity for Light Bulb Networks [pdf] - vinchuco
http://www.disneyresearch.com/wp-content/uploads/Linux-Light-Bulbs-Enabling-Internet-Protocol-Connectivity-for-Light-Bulb-Networks-Paper.pdf
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chrismartin
Nice. The last thing we need are a bunch of light bulbs competing for crowded
Wi-Fi spectrum.

Do you notice the LED flickering during transmission?

Would using a separate infrared emitter and photosensor increase the range?

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bcaine
If you design the system correctly, flickering should not be visible to the
human eye. Obviously that depends on factors like clock rate of your
transmission and your coding technique. As long as your signal is reasonably
DC balanced and your modulation rate switches faster than the human eye can
detect (say > 60Hz), you should be in the clear. The IEEE 802.15.7 working
group [0] proposes clock rates of 200 kHz to 120 MHz, which all should be
fine.

As for a separate IR emitter/photosensor, in theory it could increase range.
Range ends up being decided by a bunch of tradeoffs and channel conditions
that effect your Bit Error Rate (BER), which increases the further you move
away from the source. The major factors that effect BER is the noise in the
room (the ambient irradiance levels of other light sources), your transmission
power, photodiode sensitivity to your wavelength, filtering quality, area of
photodiode, and forward error correction quality. So moving to a wavelength
with less noise certainly would help tremendously, assuming everything else is
equal.

[0]
[http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=616358...](http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6163585&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6163585)

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simoncion
> ... and your modulation rate switches faster than the human eye can detect
> (say > 60Hz) ...

I can pretty reliably see pulse rates up to ~120Hz. I know of many others who
can, too. :) So, please, please, please don't give people the idea (even
inadvertently) that pulse rates below 120Hz are going to be undetectable. :)

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dmritard96
The usage for low power devices is tricky. I suppose if you constantly
broadcast for the specific device in range a sleepy device could pickup any
desired changes but its a but tricky.

