LEGO® MINDSTORMS® and Technic®MINDSTORMS® EV3/NXTMINDSTORMS SensorsLEGO® technical dataLDrawMiscellaneous LEGO®LEGO® & PhotographyPanoramic PhotographyPhoto GalleryHome

 

 

 

    The Card Reader 2

    This machine is an enhancement of my original card reader. Instead of using a mechanical clock to center light reading in the middle of plates, a more complex encoding ensures that there is always a light transition between plates, thus enabling synchronisation. A state machine defines color sequence:

    Present state

    Color

    Coded bit

    Next state

    0

    Yellow

    0

    2

    0

    Grey

    1

    1

    1

    Black

    0

    0

    1

    Yellow

    1

    2

    2

    Black

    0

    0

    2

    Grey

    1

    1

    The first plate is always black (to locate transition between card reader background and begining of card), and state machine starts in state 0.

    Some encoding samples:

    Value

    Card

    0

    B Y B Y B Y B Y B Y B Y B Y B Y

    9876

    B Y G B Y G Y B G B Y G B G B Y

    11111

    B Y G B G B G Y B G Y B Y G Y G

    12345

    B Y G Y B Y B Y B Y G Y G B Y G

    22222

    B G B G B G Y B G Y B Y G Y G B

    31415

    B G Y G Y B G B G B G Y B G Y G

    32767

    B G Y G Y G Y G Y G Y G Y G Y G

    A small basic program encodes any value between 0 and 32767.

    This new version is mechanically simpler and runs much faster (16 x !) than the previous one. It is also probably more sensitive to errors, but after some tweaking of values it seems fairly reliable. Adding diffusing tape below light sensor (see photo) avoids specular reflection on Lego plates and also improves reliability. An other improvement is the addition of a touch sensor to start the card reader when a card is inserted in the reader.

    Update January 2001: the Card Reader 2 is the base of my Brick mixer 

           

LEGO® MINDSTORMS® and Technic®MINDSTORMS® EV3/NXTMINDSTORMS SensorsLEGO® technical dataLDrawMiscellaneous LEGO®LEGO® & PhotographyPanoramic PhotographyPhoto GalleryHome