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Date: | Tue, 6 Apr 2004 09:24:44 -0400 |
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Hi,
The talking sign project used FM modulated lights over doorways and exits
and it worked pretty well. I'm surprised that the concept never took off.
Bob Tinney, K8LR, [log in to unmask]
Always trust the person looking for
the truth,never trust the one who's found it!
----- Original Message -----
From: "Brent Harding" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, April 05, 2004 11:48 PM
Subject: Re: voice modulated light?
Why would one want to modulate voice over light? How far away could such a
signal be transmitted compared to infrared TV remotes?
----- Original Message -----
From: "Martin McCormick" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, April 05, 2004 2:14 PM
Subject: Re: voice modulated light?
> That is somewhat of a broad question. Most light sources
> except for incandescent bulbs can be modulated. Even incandescent
> bulbs can be modulated, but they can't change brightness fast enough
> to produce much audio.
>
> Most of the schemes I know anything about for sending audio
> over light involve using a fluorescent tube or even a LED since those
> light sources are much faster at responding to changes in electric
> current than are incandescent lamps.
>
> The LED or fluorescent lamp is run at some frequency which is
> way too high to hear. That carrier is then frequency-modulated. A
> receiver need only have a photo detector capable of decoding the
> carrier. The rest of the receiver could be any FM radio once the
> photo cell receives the carrier.
>
> It is even possible to modulate an infrared LED with
> a fast-enough stream of digital data to cary audio and even voice.
> That is how the photo detector works in your CD player to begin the
> process of turning a flashing stream of light in to music.
>
> Martin McCormick
>
> Jim Stevenson writes:
> >From light bulbs to lasers to ir devices,
> >what equipment can modulate them with voice?
> >
> >a.m or f.m?
> >
> >Thanks much again as always.
> >
> >73
> >wb6 yoy
> >
> >(650) 604-5720
> >
>
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