go to http://www.hpcalc.org  they have technical documents which detail
the IR hardware in the hp.

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On Fri, 2 Jul 1999, Jamil J. Weatherbee wrote:

> It appears to be just async over IR.  1200 Baud, N, 8, 1.  There is no
> 40kHz carrier or the like,not like a remote control.
>
> The async over IR seems to be perfectly valid for IRDA application from
> what I have read insofar.
>
> The signal was provided by:
> 1) the IR transceiver from a lego mindstorms kit
> 2) my HP48GX
>
> they look pretty much the same, I would guess just a UART connected
> through maybe a switching transistor which switches the current on and off
> through an IR diode (my guess, but I am new to this).
>
> So that when the UART outputs 0 (low) that turns on the IR diode.
>
> On Fri, 2 Jul 1999, Tom Handley wrote:
>
> >    Jamil, what is the transmitter pulse rate and what kind of modulation?
> > Is it a TV/VCR/etc remote?
> >
> >    - Tom
> >
> > At 09:11 AM 7/2/99 -0700, Jamil J. Weatherbee wrote:
> > >It is an IR phototransistor not a photodiode, so I didn't think I would
> > >need amplification, just a pull up resistor.  But the output at the
> > >collector then doesn't seem like it will work very well with a ST input
> > >because it takes a long time for the output to rise back to 5 volts after
> > >it is exposed to IR.  I have it setup as a 10k resistor connected to +5V
> > >and to to IR phototransistor collector, with the emitter connected to
> > >ground.  I've put the Vcollector on the oscilliscope, and have been able
> > >to see signals from a IR transmitter by triggering on a negative going
> > >edge.
> >
>