After pondering the distance covered by their daughter's pet hamster in a spnning wheel, Jamie Bailey turned to the world of Raspberry Pi for a solution. They have used a laser beam break sensor to detect rotations of the spinning wheel, and with some custom circuitry have devised a system that allows the pulses from the circuit to be measured via some code in python, and the restuls can be viewed in graphic or numerical form.
It's an interesting example of capturing external sensor data with a Raspberry Pi and also gives you the framework to create (for example) a bike computer or a device to measure rotations of almost any form.
If you're interested in detecting changes in magnetic fields with your Arduino, or counting revolutions of a wheel - you can use a hall effect sensor and we have a convenient module just for the purpose - our HALL: Hall Effect Magnetic and Proximity Sensor Module. It operates on both 3.3 and 5V boards, can detect both north and south pole magentic polarity and shows when triggering is successful with a convenient LED.
To learn more about the HALL: module, read our Quick Start Guide and to order, visit out HALL: product page.