We've built an Arduino-powered device that feeds plastic "sand" into river models (www.emriver.com
) for research and teaching. It uses a stepper motor and cone valve.
This video shows the business end: http://youtu.be/KMMfNxQmqh4
If we can measure the velocity of the particles through the tube, and we know its cross section (it's 0.75 inch diam) we can know the feed rate.
Seems an optical mouse sensor would be perfect. I see Sparkfun had a breakout for one (http://www.sparkfun.com/products/10105
), but discontinued it.
And hacking a USB mouse is complicated. Any ideas?