· Card Reader

December 2004
          

This robot can read little color-coded cards and perform different actions depending on the card read.

Top view. The arrows indicate the slot to enter the card, the touch sensor with the green light next to it starts reading. A rotation sensor allows the robot to know the exact positions of the color strips on the card. It is directly connected to the motor that drives the pull-in mechanism.

Front view. The tires that pull the card in are clearly visible, as well as the rotation sensor. On top of the construction is a light sensor pointing down, allowing the robot to "see" the color strips.

This is a sketch of the cards. The left end is positioned in the reader, and pressing the sensor (with the green light) causes it to be dragged inside completely. It is then read and returned to you.

A card consists of 4 segments that are either black or white. The light sensor reads the segments and creates a binary number out of them, white is a 0 and black is a 1 (therefore each card has its unique number, allowing you to make up to 16 different cards).
The card displayed above would read (right to left):
WHITE-BLACK-WHITE-BLACK = 0101 = 0*8+1*4+0*2+1*1 = 5

Reading a card.
The other touch sensor (next to the red light) is designed to calibrate the reader by measuring the values of a white and a black segment to be able to differenciate them under any light condition. To calibrate, it must read the card depicted above (0101).

More views from different sides...

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