Marker Rack


The Marker Rack is a house for Prismacolor markers that interacts with users by rattling markers as the user’s hand passes over them and lifting any specific marker when the user’s hand hovers over it.


How it works

  • When a hand is placed over the markers it reflects IR light from the IR LEDs, in front of the markers, to the IR sensors behind the markers.
  • The program triangulates the position of the hand and tells a servo, with a large gear head, to move to a correct angle.
  • The servo gear head moves a rack gear back and forth parallel to the row of markers.
  • If the hand stays in the same location, an arm connected to the rack gear, is pushed up and forward by a small linear actuator (taken from a walkman CD player).
  • The arm pushes up a lever that raises the marker above it.
  • The arm retracts and the gear rack continues to follow the hand.

Diagrams and Photos


(with help from max)

The code works by taking a running average each IR sensor. It then finds which sensor has the largest input. Because the markers are evenly spaced, the position of each marker is given a number and mapped with the correct angle range of servo. Once the program has found the sensor with the highest value it uses the servo to move the arm toward that sensor one marker at a time. The program also counts how long the servo has been in any given position. If it has been in any position for given length of time it extends and retracts the arm that pushes up the marker. The arm is pushed up using an H-Bridge so the program sends a high signal for a second, turns it off, and then sends a high signal through a second pin.


  • Foam Core – for frame + gears
  • Mat Board- for other parts of the frame
  • Dowels- for the axis of the marker hinges and the marker levers
  • Tubing- also for the marker hinges
  • Balsa Wood- for the pusher arm
  • Plastic Sheet- for the arm that rattles the levers
  • 5 IR sensors
  • 5 IR LEDs
  • Servo Motor
  • Linear Actuator (from a CD player)

~ by chrisioffreda on April 1, 2010.

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