From: dstamp@watserv1.waterloo.edu (Dave Stampe-Psy+Eng)
Subject: Re: Cheap Head Orientation Sensors
Date: Wed, 27 Nov 1991 02:33:14 GMT
Message-ID: <1991Nov27.023314.25648@watserv1.waterloo.edu>
Organization: University of Waterloo


clarke@next1.cs.ucf.edu (Thomas Clarke) writes:

>Horizontal is easy using the electronic automotive compass available 
>from Radio Shack (don't have part number to hand, but cost is about $50).
>
>A little black flux-gate sensor head (same source as Polhemus?)
>is connected to an electronics box with a rotating indicator dial.

Sounds like you'd get an angle-related output but here's 2 problems:

- Magnetic field varies greatly with position near any metallic object.
You probably couldn't use it indoors or near monitors (LOTS of noise!)

- Gain will vary with vertical head orientation.  This could be fixed in 
software.

>For vertical orientation, we are investigating the use of gravity reference.
>First thought was a joystick mounted upside down with a weight.  
>There are also electronic vertical sensors.  One catalog lists an electronic
>level for about $50 with an LCD readout.  Depending on what's inside the  
>interface could be difficult (worse case - potted electronics).  

I dunno-- what you want is an electronic inclinometer: a level will probably
give only a couple of on-off outputs.

If you do find an inclinometer, you'll have 2 problems:

- Oscillation after changes in head angle.  This could be greater in
amplitude than the head movement, and last for 1-2 seconds.

- Forward-backward motion crosstalk (accelleration)

If you manage to beat these, and it really IS an inclimometer, it sounds nice.
Good luck with the magnetic thing, though.  You might think about setting
up some large 200 Hx (or so) magnetic fields with large-diameter coils, and
add filters to the outputs.

--------------------------------------------------------------------------
| My life is Hardware,                    |                              | 
| my destiny is Software,                 |         Dave Stampe          |
| my CPU is Wetware...                    |                              | 
| Anybody got a SDB I can borrow?         | dstamp@watserv1.uwaterloo.ca |
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