Over ten years ago, I put up a web page with detailed instructions on building a simple electric motor based on one from the Beakman's World TV show. I called it the "Beakman's Electric Motor"
page and over the years it has had hundreds of thousands, if not millions, of hits. Realizing that just building a motor, no matter how cool, wasn't a good science fair project, I added suggestions for using the motor as a science fair project, such as experimenting with different magnets, batteries, and coil constructions and seeing how they affect performance. In order to do this, the speed of the motor should be measured, but I left that as an open-ended question.
I've had dozens of e-mails over the years asking how to measure the speed and I've always suggested using a broken light beam and a counter, but I've never built one myself. I even suggested to one person that they use a slot-car lap counter since I'd seen on one sale at Toys 'R Us for 99 cents and she said that it worked perfectly, but not everyone can find a good deal like that.
It just so happened that I got one of these "how do I measure the motor speed?" e-mails on the same day my new Arduino Diecimila
microcontroller board arrived from the Make Store
, so I thought that would make a great weekend project.
Here is the result, an optical tachometer for Beakman's Electric Motor using an IR emitter/detector pair and a Arduino board. With a few modifications to the programming, you can use this tachometer for measuring other things such as fan or propeller speed. Notes are included on what to change for different applications.How to have fun with Arduino
is a good source of basics on how to setup and use the Arduino board.