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
> >
>