speedometer project

Posted on Feb 5, 2014

A simple low cost Infrared LED speedometer is described that can be fitted to a skateboard, longboard or even a bicycle to measure speed. Notes on building, setting-up and calibration are given. When used with a low cost data logger continuous measurements of speed can be made while out-and-about. The device forms an interesting science club project and would be

speedometer project
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a great introduction to potential physicists and engineers to scientific instrument design, testing and calibration as well as to generate lots of their own interesting data to analyse. Fig. 1. Longboard skateboard with IR speedometer circuit attached underneath the board. The electronics is housed in the small di-cast box under the board (right). Skateboarding has been around for at least 60 years but in its popular form since the seventies [1]. Recently longboarding has started to become popular with adults as well as with children [1]. The longboard has larger wheels and wider trucks than skateboards making it more stable for adults as well as better equipped for commuting and long trips. YouTube videos show that people are now using longboards on 2000 km treks! [2]. As longboards are generally better made and larger than skateboard they are easier structures on which to develop instrumentation and measurement equipment. It`s great fun to combine science, instrumentation and longboarding. Here we use Infrared (IR) light to monitor the speed of rotation of one of the wheels. Light from an IR LED is directed at one of the wheels. The wheel has a small reflector fixed to it (see below) and when it rotates into position it reflects a signal back to an IR receiver. On reception of the IR beam the receiver o/p pulses low (0V) for a short period. These pulses are too variable to monitor directly but we use them to trigger a...

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