Outfitting a Cat Exercise Wheel for Gathering Data on Zoomies

Every pet owner must contend with the issue of exercise. Most common pets evolved to move around quite a lot in nature as they hunted or scavenged for food. But in our houses or, even worse, apartments, they have little room for exercise. They also have consistent access to high-quality food, which means that weight gain can easily become a problem. For cats, exercise wheels (similar to those commonly associated with hamsters) can be a great source of activity. To gather data on his cat's activity, Scott Cutler added a bit of hardware to a cat exercise wheel.

This is an exercise wheel from One Fast Cat, which Cutler received from a friend when their cats refused to utilize it. As an exercise wheel designed for cats, this is pretty large. The inner surface is lined with grippy material so kitties can get traction, and the other surface has two protruding tracks that ride on rollers on the base. Cutler's cat Cygnus seems to enjoy running on the wheel and Cutler wanted quantified data on that exercise. Cutler realized that he could gather information on the wheel speed, direction of rotation, and the frequency of activity with a minimal amount of hardware.

Cutler chose to utilize the conventional sensor solution for something like this: Hall effect sensors and magnets. Cutler glued some permanent magnets around the outside perimeter of the wheel (eight magnets arranged evenly). Two Hall effect sensors place near each other at the bottom of the wheel on a 3D-printed mount detect the magnetic fields.

The spacing was important for calculating direction. If Cutler only cared about speed, he could have used a single Hall effect sensor. To calculate direction, he put the two sensors close together — much closer together than the distance between magnets. That means that a magnet will trigger one sensor and then almost immediately trigger the second sensor, before the next magnet comes around. By checking the order in which the sensors register the magnet, the system can determine direction.

An ESP8266 development board monitors the two Hall Effect sensors. It performs the calculations and then records the three data points: speed, direction, and time. Because the ESP8266 has a built-in Wi-Fi adapter, Cutler can easily access the data to see what Cygnus has been up to.