I had a broken bike computer.
Clearly, when one has a broken item, their obvious inclination is to try and fix it. Much of the development on this project was done early in my exploration into electronics and Arduino, but was not completed until I had a functioning 3D Printer with which to make the case. The computer is now attached to a stationary exercise bike, which resulted in the addition of a couple features beyond that of a simple speedometer. An RGB LED indicates how close the rider is to an adjustable target speed, and there is also a timer function with an alarm to signal completion of an exercise routine. I have not yet tried to mount the computer on an actual in use bicycle, but that is on my list of future projects.