From: clarke@next1.cs.ucf.edu (Thomas Clarke)
Subject: Cheap Head Orientation Sensors
Date: Mon, 25 Nov 91 14:15:01 GMT
Organization: University of Central Florida



Partly out of thrift and partly out our dislike for the limitations of 
both transmitter/reciever magnetic and acoustic technology, we have been 
investigating simple home-brew head orientation sensors.

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.

The dial is basically a meter movement with crossed coils so that it can 
rotate a full 360 degrees.  Looking inside the voltages across what are
obviously the two sets of meter terminals are proportional to the 
components of the earth's field along the two axes of the sensor.  

Digitize these voltages, and a little math (arctan) gives horizontal 
orientation of the head to which the sensor is attached.  Sensor cable
is a little short, but could be extended.

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).