Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!usc!ucsd!sdcc6!sdcc13!pa1409
From: pa1409@sdcc13.ucsd.edu (Steven Haehnichen)
Newsgroups: comp.sys.handhelds
Subject: Re: Easy HP infra-red PC receiver.
Message-ID: <5941@sdcc6.ucsd.edu>
Date: 6 Jan 90 05:59:57 GMT
References: <5916@sdcc6.ucsd.edu> <10169@microsoft.UUCP>
Sender: news@sdcc6.ucsd.edu
Organization: University of California, San Diego
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OK, it looks like the Radio-Shack IR detector has some "features"
that make it impossible to read HP printer signals.  <sniff>

I received some informative mail bringing to my attention the
built-in low-pass filter that effectively filters out anything
useful from the HP28S.  The papers state that the receiver detects
and filters out a Bandpass Center Frequency of 40 kHz.  I wish I
knew the exact frequencies used by the HP-IR, but someone said that
an oscilloscope shows that the carrier was detected but the data was
NOT demodulated correctly.

(I accidentally wiped the mail with all this info, address included,
so I apollogize for not giving credit to whom it is due.)

BUT, I'm not done dreaming yet...
Would it be possible to write a program (IMC?) that would pulse the
LED at a lower frequency, making it readable by the Radio Shack
gizmo?  Apparently, there is no problem with the 40 kHz carrier,
just the data on it.  Really, it doesn't need to be the same HP
protocol at all, just readable signals.  I have a feeling that
anything would be faster, more accurate, and more convenient than
entering code by hand. (helluva lot more fun, too!)
How accessable is the IR-LED to software?  (sorry if I'm resurecting
a past well-beaten topic; I've only been on this newsgroup for a
month or so.)

One other thing... I'm no electronics buff, but how hard would it be
to kill the low-pass filter on the receiver.  (Would it solve the
problem?)  The only pieces on the board are the phototransistor, IC,
a couple of resistors, and a 47uF capacitor (can barely read it).
Would that be part of the low-pass filter? (i.e. a chageable part)
How far off-base am I here???

Steve Haehnichen
shaehnichen@ucsd.edu and probably any other general UCSD path.
---
"May your dreams be longer than the night."
					      - Vangelis