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.
>