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From: pepke@gw.scri.fsu.edu (Eric Pepke)
Newsgroups: sci.electronics
Subject: Re: Power Glove
Message-ID: <1020@sun13.scri.fsu.edu>
Date: 5 Oct 90 19:05:34 GMT
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Organization: Florida State University, but I don't speak for them
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The Spine-Chilling Saga of the Power Glove, Part 2

I got an MC68705S3 processor from Motorola.  I also got a board for 
programming it, which Motorola sends out for free.  It is designed to copy 
the program from an external EPROM to the processor's built-in EPROM using 
a bootstrap program in the processor.  It also has a connection for an IBM 
PC printer cable so that you can program it without going through the 
extra step of programming an EPROM.  Unfortunately, the sections of the 
documentation that refer to this process have statements like, "Do not 
use!  Does not work yet!" scrawled over them.  It's hard to imagine how 
the hardware connection could fail to work.  Maybe they mean the software. 
Further experiments will have to wait until I get the parts to make the 
programmer work and I replenish my stock of IC's for experimentation.

Meanwhile, I have been doing some thinking about the math involved.  The 
time for a signal to get to a receiver gives you a distance, which you can 
think of as the radius of a sphere.  Three receivers give you three 
spheres.  Two spheres intersect in a circle (if they intersect at all).  
An additional sphere usually intersects with a circle at two points.  The 
two points reflect each other in the plane determined by the centers of 
all the spheres.  If you know that the glove is in front of the sensors, 
you can choose the point in front of the sensors.

Now, in the general case, it takes a fair amount of trig to solve this 
problem.  Fortunately and unfortunately, with the power glove as it is 
normally used, this is quite simplified.  First of all, one deals with a 
fairly small delta around a predetermined center.  Knowledge of the three 
radii for the center can be introduced into the equations at an early 
stage to get an inexpensive simplification.  Second of all, the distance 
to the sensor array is large compared to the spacing between elements of 
the array, though not too large.  Effectively, this means that the hard 
3-D problem can be approximated by two easier 2-D problems.

This is fortunate, because it simplifies the amount of processing that the 
power glove has to do.  It is unfortunate, because it probably means that 
the designers of the software made those approximations, which may mean 
that figuring out how to program the internal processor won't help if you 
want to do something very sophisticated.

Of course, I have a vested interest in justifying the effort I am making 
in replacing the procesor for one of my own, which may affect my 
willingness to believe this.

Eric Pepke                                    INTERNET: pepke@gw.scri.fsu.edu
Supercomputer Computations Research Institute MFENET:   pepke@fsu
Florida State University                      SPAN:     scri::pepke
Tallahassee, FL 32306-4052                    BITNET:   pepke@fsu

Disclaimer: My employers seldom even LISTEN to my opinions.
Meta-disclaimer: Any society that needs disclaimers has too many lawyers.