Electronic Compass Investigation
 (May 2004)

I purchased an electronic compass for possible use during our BEAR HAB flights to show the direction a camera was pointed when each photo was taken.

I purchased this compass in the auto dept of Canadian Tire for $39.99 Canadian, but the same unit was also found on the web under various different names from $39 to $59 USD.

Opening the unit without destroying the plastic case wasn't easy as GLUE was used in addition to a number of screws.

For information on the operation of the magnetic field sensor in this unit, refer to the following manufactures literature:

KMZ52 Data Sheet
KMZ52 App Note
General Magnetic Field Sensors Data Sheet
Earth Field Sensors

Left - The sensitive KMZ52 magnetic field sensor I.C. with two magnetoresistive thin-film permalloy Wheatstone bridges with integrated compensation and set/reset coils. The I.C. is on a small circuit board that's at an angle to the main circuit board so the I.C. will be nearly level when the compass is used in an auto with the display tilted at a typical viewing angle.

I realized that a 2 axis compass depends on the I.C. being level with the earths surface for accuracy and that we would likely require a much more expensive 3 axis compass that uses a third sensor to eliminate the tilt problem, but I wanted to see just how critical it was to keep a 2 axis compass level which turned out to be very critical and make a compass like this totally useless for our application.

The LCD display interfaces with the long multi-conductor strip along the bottom of the photo. The microprocessor chip that interprets data from the KMZ52 and functions as the LCD controller is embedded in the blob of black epoxy.

The tiny silver cylinder with 2 leads is the microprocessor crystal. One of the two I.C.'s is a quad op-amp used to amplify the small output voltages from the KMZ52 circuit.

More details may follow if a use for an inexpensive 2 axis compass is ever found.