Pulley Rotation Sensor

The sensors attached to this pulley can be used to measure the rotation of the pulley and the linear motion of a rope passing over the pulley. This pulley can be used as part of an Atwood machine.


  • Laser-cut 3mm acrylic parts
  • Pulley
  • Printed paper pattern
  • Rubber cement glue.
  • Two Grove IR reflective sensors
  • Four M2 10mm machine screws with nuts
  • Four 1.25" 1/4-20 bolts with nuts
  • Two large 1/2" inner diameter washers
  • Thin 1/2" inner diameter washer
  • 1/2" inner diameter, 3/4" outer diameter, 1/2" long bushing
  • 1/4" inner diameter, 1/2" outer diameter, 3/4" long spacer

Note: We assume that the printed pattern is pre-attached to the pulley using the rubber cement glue.


  1. Place three 1.25" bolts through the triangular acrylic.
  2. Add the 3/4" long spacer and small black washer.
  3. Add the pulley with the printed patterns facing upward.
  4. Add the two large washers.
  5. Attach the 1" bolt and nut to the small acrylic part with a hole in the center.
  6. Assemble the remaining parts and secure the assembly with the 1.25" bolts and nuts.


A sample sketch is available that shows how to use the WireGarden library to read from the sensor. You can use the Arduino Programmer to send the sketch to your Arduino, or you can download the sketch. This sketch depends on the WireGarden library.