Ok, I feel like a complete idiot, I don't know what effect exactly I was
seeing but check out http://www.hpcalc.org/docs/misc/ioport.txt it shows
some ascii diagrams for the transmit and receive circuits in the HP48, I
think I can directly interface.  At least I had the right idea on the
transmit circuit :) !!


On Fri, 2 Jul 1999, Lynx {Glenn Jones} wrote:

> go to http://www.hpcalc.org  they have technical documents which detail
> the IR hardware in the hp.
>
> ------------------------------------------------------------------------------
> A member of the PI-100 Club:
> 3.1415926535897932384626433832795028841971693993751
> 058209749445923078164062862089986280348253421170679
>
> 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.
> > >
> >
>