On Tue, Apr 03, 2007 at 11:10:10AM -0400, Scott Touchton wrote:
> How about using a Piezo-electric element as a knock sensor.  Glue it to the
> block, filter and amplify.  

This will work.  I have used an electret microphone to measure the compression
waves produced by the swinging prop.  The circuit for the motor tachometer is
in the top of the scehatic on this page:
http://coledd.com/electronics/flight_controller
Plug a mic into J13, and time the pulses coming off the TACH line.

Take care,
-Chris

-- 
| Christopher Cole, Cole Design and Development               cole@coledd.com |
| Embedded Electronics and Software Design                  http://coledd.com |
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