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:

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:

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 

• Download the LeoCAD design files
   
• See step-by-step instructions

  1. Light sensor, base and final assembly
  2. A sample card
     

• Download the encoder program (basic)
• Download the source files

  1. Reader program 1, using NQC 2.0 and fixed light thresholds. Reads the value and keeps it in a variable.
  2. Reader program 2, using NQC 2.2 and adaptative light thresholds. It requires to upgrade your RCX to 2.0 firmware (get the update). This new firmware enables to display user values on RCX LCD, here the four lower figures of the read value are displayed on the LCD digits while the decimal point shows the fith figure.

• Photo Gallery