Programming instructions

accessories
sensor accessories
Optical Shaft Encoder Kit, continued
Optical Shaft Encoder Kit • 3
For More Information, and additional Parts & Pieces refer to:
www.VexRobotics.com
Technical overview continued
By knowing how many slots are cut into the encoder wheel, we can determine how many
revolutions the robot wheel has made based on the number of times the light sensor has
picked up illumination from the LED. The encoder wheel included in this kit has 90 slots.
By mounting a shaft encoder on the axle of one of your robot’s
wheels, you’ll be able to determine how many times that wheel
has rotated. That, in turn, can be used to calculate the distance
the robot has travelled, based on the diameter of the wheel.
The Optical Shaft Encoder can detect up to 1700 pulses per
second, which corresponds to 18.9 revolutions per second and
1133 rpm (revolutions per minute). Faster revolutions will not
be interpreted correctly, resulting in erroneous positional data
being passed to the microcontroller.
This is a digital sensor, which means that the signal it will pass
to the Vex microcontroller will either be high (1) or low (0).
The sensor output is low (0) when the light from the IR LED
passes through a cutout segment of the encoder wheel and falls
on the detector, and high (1) when the light is blocked by an
1
90 tick marks (pulses) = 1 complete revolution
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opaque segment of the
encoder wheel. This
means that the Vex
microcontroller will be
receiving a string of 1’s
and 0’s as your robot
moves. The string of
1’s and 0’s will then
be interpreted by your
program and used to
determine the robot’s
actions.
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