Re: TI-H: IR Link


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Re: TI-H: IR Link



Ok... the way most IR transmissions work as far as I know is that IR
light, which, yes, is around 900 nm (the wavelength of the light), comes
out of an IR led (duh... I know this is boring, but hold on a sec) which
is connected to something like a 555 that modulates it (some word like
that) at a frequency of about 40KHz... this is a standard for most IR
transmissions... this 40KHz stuff is then send through a second pass
(which is why a 556 is more useful) through a timer and modulated again
anywhere from 100 Hz to 1000 Hz... sometimes higher if you have a good
detector... The detector finds the 40KHz light, sends the on and off of
the light w/o the 40KHz to a tone decoder, which searches for tones in
between 100 and 1000.... if it finds it, it's happy...


Here's a diagram... (this probably won't help any... but here goes)


+-------------------------------------------------------------+


     ----------------                 ----------------
     | /\ /\ /\ /\ /|                 | /\ /\ /\ /\ /|
     | || || || || ||                 | || || || || ||
     | || || || || ||                 | || || || || ||
     | || || || || ||                 | || || || || ||
------ / \/ \/ \/ \/------------------- / \/ \/ \/ \/-----------


the big on and offs are the 100-1000 Hz frequencies and the small ones
inside are the 40KHz frequencies...


+---------------------------------------------------------------+


Also, I don't think the idea of sending only when one of the wires is high
would work because if there was interference of anykind, the receiving
side would immediately go low, screwing up the whole transmission....


I think you'd need to use flip-flops or something to that effect so the
circuit would remember the last thing sent to it, and leave all wires at
the state they were at until told otherwise... this way transmission
errors would not happen very often since the sending port doesn't change
any of its wires until the receiving one does...


					-Joe
				joschnei@sendit.nodak.edu










On Thu, 10 Mar 1994, Steve Wrobleski wrote:


> ti-hardware@lists.ticalc.org wrote:
> > 
> > >3) I don't know how well two separate wavelengths of light would work,
> > >they might interfere with each other. I've tried to find out, but no one
> > >seems to know and I haven't tried myself.
> > 
> > The two wave lengths shouldn't interfere with each other.  But tell me,
> > where is says "transmitter", and tells you the wave length, where do you
> > buy a 950MHz ir transmitter?  Don't you have to build one?  What do you
> > have to do to oscilate the binary values. I'm assuming that it will work by
> > sending out a constant signal at the specified w-l for 'on', and nothing
> > for 'off', right?
> > 
> >                                    -C.J.-
> > 
> > ********************************************************************
> > Unsolicited commercial e-mail to the poster of this message
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> > 
> > 
> > 
> 
> Its not mhz, its nm. It is a different color of light. Some ic's send
> off/detect different color light better because of the stuff that is
> added too them. The 900 nm will pick up insignificant amounts of 950 nm
> radiation and vice-versa
> 
> --Steve
> 


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