Dabbling with IR Communications

From the Pacific Grove Tribune...

     POLICE BLOTTER  Saturday, Sept. 8, 1984

12:39 am  Suspicious circumstances near 200 2nd.
Officers contact an 18-year-old man and his friend;
both have been climbing telephone poles.  The man
says he is conducting experiments with a laser
beam.  Officers say he should conduct his experiments
[ appliance ] Message 68: Fri Jan 20 1989 1:59am
From: Zaphod, Fugitive Galactic Prez
Subject: Armory Attacked by Laser!!!!

    well actually not attacked.  just beamed at, by Matthew's 2 mW HeNe laser.
I was eating dinner when he walked in and said, "the beam is about this big"
(shows 30 cm circle).  Took me a moment to figure out what he was talking
about.  Went out, and lo and behold, there was a bright red circle bouncing
around the front of our attic (bouncing because it was being obligingly held
by Eric at the House).
     What we will do:  to start, I think we'll make an ordinary IRED xciever
system, forgoing lasers at the moment in the interest of actually getting 
something done.  Perhaps a digitally controlled tranmitter, which could be
remotely keyed by equipment that would start out PWM'ing or FM'ing it to 
encode voice, and later send data.  
     Making it a simple RS422 communications device might be
best; that way it could be used to connect my '386 if/when I get it and am
running Xenix, and his Mac II running (eventually) A/UX, via ports.  19.2
or 38.4 would probably be enough.  Maybe faster later with a real laser link.
[ whine ] Message 10297: Sat May 16, 1992  7:46pm
From: Zaphod, Galactic Prez (spcecdt@ucscb)

     We have line-o-sight between Armory & Echo!  I'm astounded!
I thought the chance of it was *really* low.  But no.  A few hours
roaming about roofs with binoculars and compasses and HTs and we
discovered a *great* path - no need for towers or anything.  I
can even see the top of Tim's window :)
     Then matthew gave me a 10.2GHz FM receiver made out of a
radar detector and we got *microwave audio* working!  Yowza!
We really *are* going to have a network link.
     Interestingly, I find that Echo is within a couple of degrees
of magnetic south from here.
[ whine ] Message 10336: Sun May 17, 1992  4:31pm
From: Zaphod, Galactic Prez (spcecdt@ucscb)
Subject: what we need...

    We could probably get by with <10Mbps, but the next step down is serial
port speeds, say 38.4Kbps, because convincing an Ethernet card to operate at
anything other than 10Mbps would likely be rather difficult, and serial and
Ethernet are the only reasonably priced communications adapters for PCs.
    A 38.4 PPP link would be fine for non-interactive things like News
transport (1-2M per day of News goes from gorn to deeptht), mail, etc., and ok
(just barely) for a few interactive sessions (logins, talks, etc.), and
annoying but workable for things like ftp, but we need much higher rates for
NFS and X and such.
[ ham_radio ] Message 241: Tue May 19, 1992  7:02pm
From: KC6QKZ (spcecdt@ucscb)
Subject: StarLan

     If it turns out to be really hard to do 10Mbps, we should look into
the StarLan cards.  But I picked up those Ethernet cards for $80 each...
and there are much cheaper ones; I bought the WD cards because SCO TCP/IP
only supported a couple of types at the time and they were the cheapest.
I'll hafta keep an eye out for StarLan cards; see what they go for used.
     For our purposes, I think Ethernet cards are just fine.  We'll be
taking advantage of the high bandwidth, but a particular process' network
communications tend to be *very* directional, and the probability of the
network being pushed in both directions at once is low enough that I doubt
we would even notice the difference if it were full duplex.  Also, SCO TCP/IP
doesn't support synchronous serial cards, nor does the SCO serial driver,
so you can't use PPP or SLIP unless you can find a SCO-compatible serial 
driver, and if you do the load on the system will be outrageous (and I'd guess
the cost would be too).
     So... with Ethernet cards being cheaper, easier to use, and faster...
I think they're a good plan :-)  We're likely to get a really excellent
connection up for amazingly little money.
     btw, the Armory and Echo are 800m from each other as close as I could
measure on a map.  With a 51uS slot time that should be no problem :-)
We will also need cables with 4 individually shielded 20 or 22 gauge twisted
pairs, with overall shield, for the run from AUI port to tranceiver, so we
should be on the lookout for that too.
This web page maintained by John DuBois