MONITORING DEGU ACTIVITY
My next step for this project
is to measure Cheech's speed and direction running in the wheel.
Watching him, it would seem he runs more toward the front of the cage than
toward the back.
We need more information. Time for more electronics and a computer chip.
Calculations
Cheech's wheel measures 11 7/8 inches inside diameter.
The circumference of a circle is Pi times its diameter.
I
will use 3.1416 for an adequately precise rounding of Pi.
The running surface of Cheech's wheel is:
Circumference = Pi * Diameter
Circumference = 3.1416 * 11.875 inches
Circumference = 37.307 inches
Rounding down to 36 inches introduces -3.6 % error, negligible for this sort of experiment.
A 36 inch circumference running track works out unbelievably convenient;
Measuring to the nearest foot only requires we monitor to the nearest 1/3 of a
revolution or 120 degrees.
Sensing
One of the simplest and most reliable sensors available for this type of application is a Reed Switch.
Reed switches are in common use in Alarm Systems, Industrial Machines, Automobiles, and Nixie Clocks.
A Reed Switch consists of two contacts made of thin "reeds" of steel enclosed in a glass shell.
The reeds are bent such that they are close but not quite touching, forming an open
circuit.
When either pole of a magnet is placed near the switch,
the
magnetic field causes the two reeds to attract each other, closing the circuit.
When the magnet is removed, the contacts return to their open position.
Rotation Sensing
With a magnet mounted so that it rotates with the wheel and
passes near a reed switch each revolution,
we can easily count the revolutions
of the wheel.
With a Microcontroller providing some timing and math, we can also calculate how fast
the wheel is turning.
Using three equally spaced magnets and a reed switch, we will
have a switch closure for every foot that Cheech runs.
The Heisenberg Uncertainty Principle
states that one can never be absolutely certain of both the position and
velocity of
a subatomic particle.
The Degu Uncertainty Principle
states that one can never be absolutely certain in which direction Cheech will
decide to run in his wheel.
(As hypothesized by John Miktuk on March 15, 2006)
Rotation and Direction Sensing
Knowing the Degu Uncertainty Principle, we need to monitor both distance and direction.
We will use three equally spaced Reed Switches and one magnet:
When the wheel turns in a Clockwise direction, the
microcontroller will hear
"...ABCABCABCABCABCABC..."
When the wheel turns in a counter-clockwise direction, the
microcontroller will hear
"...ACBACBACBACBACBACB..."
The combination of one magnet and three reed switches
provides the microcontroller with
all the input it needs to determine how fast
and in which direction Cheech is running in his wheel.