Introduction: Direction Aware Messaging LED Spin Top

We recently built a LED spinning top with message display. Its an
improved version of a similar top published by Elektor in their
December 2008 issue. The Elektor top can be spun only in one
direction. The synchronization required to print message on the LEDs
arranged along the radius of the top is achieved by detecting the
earth's magnetic field.

Our top can spin in either direction and print a message accordingly.
In our improved version of the spinning top, we used 2-channels of
magnetic field detector circuit placed 90 degrees apart along the
circumference of the circular PCB, to provide quadrature phase output
that allows the top to detect the direction of spin and thus is able
to adjust the LED pattern appropriately.

The top uses a Tiny44 microcontroller and is powered by 2x1.5V AAA
size batteries with a MAX756 DC-DC converter to provide the +5V power
supply to the circuit. The circular PCB was made on the Modela milling