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[on:]

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?

[Reply #1 on:]

put a vane(??) in the tube - based on length of vane seen in sensor = v
you would have to test different v's to get length...

never-mind - I reread your post - sand not water - sorry!

[Reply #2 on:]

Sensor: http://www.alpha-crucis.com/en/drone-accessories/2911-optical-flow-sensor-3700386988530.html
Code: http://code.google.com/p/arducopter/wiki/AC2_OptFlow

I see that DigiKey sells the chip only for under $4.

Not the easiest stuff to start from but a little better than starting from a random USB mouse.

[Reply #3 on:]

Hack an old RS232 mouse instead? Can likely find one at computer old/surplus store.

[Reply #4 on:]

It would be interesting to calibrate. Using an Optical mouse would/should be easy just get to the optical sensor... they use standard grey code... It would be interesting albeit somewhat dangerous to provide charge and monitoring for Cell Phone batteries, they hold an enormous amount of power VS weight, the batteries ARE Dangerous if mishandled... Only thing that was close were the old Pola-pulse batteries from the OLD Polaroid cameras about 10 CM  X  12 CM  X .4 CM and good for a couple hundred MA for short pulses, camera feed motor and flash. as to the optical mouse there was some information about serial meeces a seial stream thet gave information about the X Y movements and the computer parsed the data for clicks and number of steps X and Y, button status and placed the cursor... The Apple mice were even easier as they were really dedicated serial 4 wires not those usb/ps2 things

Doc

[Reply #5 on:]

This thread seemed a little "old" but parallax has a sensor that might fit the OP's needs and seems easy to interface to although as per their usual custom it's a little pricey.

http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/677/Default.aspx?txtSearch=mouse+sensor

[Reply #6 on:]

Thanks all!  We're still working on this and are excited about using these sensors to develop open-source science teaching tools.  The Parallax sensor would do the job, and I found this interesting site with Arduino-based mouse hacks and even some OSX visualization tools:  http://hackteria.org/wiki/index.php/Hacked_Optical_Mouse