On Sat, Apr 28, 2001 at 08:22:04PM -0400, Travis Bemann wrote:
> It would not be very hard to rig laser communications. Just have a
> laser and hook it up to a computer which turns it on an off very
> rapidly according to the data that is being sent, and have a
> photosensor sensitive to the particular frequency that the laser is
> using, which sends the data it gets to an A/D converter, which in turn
> sends it to another computer. The computer then interprets anything
> in a particular minute unit of time over a particular threshold as
> being a 1 and everything else is a 0. Mirrors are used to direct the
> laser beam, in case there is no direct line of sight between the laser
> and the photosensor.
Unfortunately it's not quite that easy (please correct me if I'm
wrong). Unless you're prepared to spend a lot of money ($100s)
on a laser you can digitally modulate you have to find some
other method of switching the light - I recently tried PWM at 11 kHz on a
laser diode from a pointer (for transmitting speech but same idea) and
I totally destroyed it. The best solution for lasers IIRC is some
type of light switch that works a bit like an LCD (I gave up and
used an LED for my project :)
As for the reciever you can square it easily enough with a Schmidtt
trigger or something similar but converting the pulse stream into
a bits is not as easy (at least with digital yau don't have to
worry so much about interference from other light sources). Firstly
you have to make sure that the trasmitter's and reciever's oscillators
are pretty much the same frequency (not really a problem if you use
xtals). Secondly you must have logic in place to differentiate the
synchronization pulses the transmitter sends from regular data, so
you know whan to start the byte to send to the computer. Not at all
impossible, just more complicated than it first seems. See RS232 or
similar.
Apologies if I just made an ass out of myself for that...
Leo
--
Leo Howell M5AKW
freenet:MSK@SSK@2vz8xnhEJyJOlBVNfBEOWaohQFEQAgE/freesite//
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