On 10/11/2011 11:16 PM, V G wrote:
> Hi all,
>
> I want to make a simple, cheap, quick, reliable (no one dare say you can
> only pick only x) garage door open detector that will light up an LED in =
the
> house/beep a speaker if the garage door is open. I know all it takes is a
> mechanical switch, but I'd rather not use any moving parts. I'm thinking =
a
> very bright infrared LED and IR transistor with a piece of foil mounted o=
n
> the inside of the garage door. If the door is closed, a series of LED pul=
ses
> will hit the aluminum foil reflector and bounce back to the IR transistor
> and signal the device that the door is closed. Will this work? I've never
> done any IR work, so I don't really know what power LED is required, what
> the distances are, etc.
>
> As for the micro controller unit, I can make it wireless and signal the
> indoor unit via something like this
> http://www.sparkfun.com/products/10534but I'd have to impliment
> encryption on the micro controller itself. It
> would also interfere with other units in the same band, which is very ver=
y
> undesirable. How hard is it to implement simple encryption?
>
> Xbee is cool, but it will add $40 at least to the cost of the project.
>
> Any other ideas?
I'm curious, why is encryption an issue?  Who, within 400 ft of your=20
garage, and with the receiver to read the signals, would care about the=20
state of the door?
As for interference, low data volume and low update frequency stuff like=20
this spends very little time on the air.    You could send one or more=20
10 mS burst at some fairly large interval (minutes) and be reasonably up=20
to date with the door.   That shouldn't be a problem unless it=20
interferes with something that is data critical.

Joe W

--=20
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