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From: pa1409@sdcc13.ucsd.edu (Steven Haehnichen)
Newsgroups: comp.sys.handhelds
Subject: Easy HP infra-red PC receiver.
Message-ID: <5916@sdcc6.ucsd.edu>
Date: 5 Jan 90 02:22:44 GMT
Sender: news@sdcc6.ucsd.edu
Organization: University of California, San Diego
Lines: 59

It has taken me a while to overcome some serious moral compunctions
in recommending anything sold by Radio Shack/Tandy, but...

I recently ran across a gadget at Radio Shack that seemed too easy
to be true, and still might be.  It's their "GP1U52X Infrared
Receiver/Demodulator"  (Catalog # 276-137).  It sounded interesting
so I bought one for about $3.50 and checked it out.  I was slightly
comforted by the name "Sharp" stamped into the tiny (1/2 inch)
tin box.  Anyway, it has a whopping three pins to it, and some
relatively useless "technical data" with it.

Ok.. The three pins are GND, Vcc, and Vout... simple, eh?
I connected the Vout to the Error line of my PC's parallel port
and put an LED on it just for looks.  I stole the +/- 5 VDC from
the key-board port and that was it.

Now my error line goes high whenever the Receiver picks up a pulse
of infra-red.  All of the support circuitry is right on the little
board.  It has an IR phototransistor, amp, limiter, band-pass
filter, demodulator, integrator, and comparator built in.

BUT... Does it pick up HP-IR?  Yup. Along with every IR remote
control I own.  The hardest part seems to be the software.  I'm not
real big on 8088 assembly, but it looks like it might be the only way 
to make sense of the signals.  (I would assume they're pretty
fast, but it seems to send a lot of data (several seconds) just for
a screen dump.)

If you set it up so that the input is fed into the Error line of the
parallel port (like mine), the fourth bit of port 0x379 will be 0 on an IR
pulse. (first bit being the LSB) so something like this works to
read it: (Turbo C)

IR = !(inportb(0x379) & 8)

Where IR is true on a IR pulse.

Anyway... to make a long story longer.. I hope someone can take it
a little further than this, ideally reading in HP text
(graphics?!?!)

I used the Error line because it lets me leave my printer on and
on-line without confusing the system, and if I mistakingly leave the
IR receiver engaged and try to print, I get a friendy printer error.

Oh, one other thing... It tends to pick up a few stray signals
(especially in bright light) but they are very few compared to the
HP data pulses.  I haven't seen it pick up any interference at all
in dim light. (One of those dark-red plastic sheilds might be nice.)

There you have it.  If anyone makes anything out of the signals,
PLEASE send me some code.  Good luck!

Steve
----------------
shaehnichen@ucsd.edu
shaehnic@ucsd.bitnet, and wherever else UCSD can get mail from.

>>> The sooner I fall behind, the more time I have to catch up!! <<<