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From: testarne@athena.mit.edu (Thad E Starner)
Newsgroups: sci.virtual-worlds
Subject: Re: VR hardware questions
Message-ID: <1991Jun25.160340.1928@milton.u.washington.edu>
Date: 25 Jun 91 04:13:36 GMT
References: <1991Jun24.153351.13571@milton.u.washington.edu>
Sender: hlab@milton.u.washington.edu (Human Int. Technology Lab)
Organization: Massachusetts Institute of Technology
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Approved: cyberoid@milton.u.washington.edu



About Polhemi:

Polhemus Boxes cost around $2000 - or so I've been told.

The address on the 3Space manual says:

Polhemus
A Kaiser Aerospace & Electronics Company
P.O. Box 560
Colchester, Vermont 05446

        
   The RTI boards people use for real time sampling aren't necessary if you 
are running a decent machine.  It spills out RS-232 at different baud rates. 
If you avoid ASCII mode (and scanf) and optimize things for UNIX
(use select and partial reads), you can easily pull stuff in at the ~60Hz in 
the background on a SparcStation 1.  Really not that much overhead for
today's boxes.  

   You probably want to multi-thread your application.

   One process to poll the box; one to sit on the RS-232, collect the data,
(optionally) filter it, and respond to queries from the higher level
application; and the application itself.

   You can also multiplex the things so that you can have a couple Polhemi
sensors running without interference.  The number of samples a sec 
is ninversely proportional to how many you run of course (2 - 30 Hz, 3 -
20 Hz, etc.).  If there is enough interest I'll post the circuit to
do the multiplexing (simple 555 circuit).  

   So far, I prefer them to Birds, but I haven't played with the Bird much.


                                Thad    
                                testarne@media-lab.media.mit.edu