AVR-Chat

--- In AVR-Chat@yahoogroups.com, "Rick" <eprom999@...> wrote:
>
> --- In AVR-Chat@yahoogroups.com, "Richard" <richardt.bradshaw@> 
wrote:
> >
> > Hi everybody I have been hanging around here for a while, great 
forum.
> > Do any of you have any experience with accelerometers? I am 
thinking of 
> > a project using an accelerometer to measure angles. The idea is 
this: 
> > the accelerometer will be on the outer edge of a wheel. As the 
wheel is 
> > turned the position of the accelerometer will move then using a 
bit of 
> > grigonometry I can calculate the angle that it has moved through. 
My 
> > question is how much accuracy can I get. I will be looking to 
measure 
> > fractions of a degree on the wheel aprox 4 inches or 100mm in 
diameter. 
> > Doing the maths gives a movement of about .88mm/degree so I would 
like 
> > to be able to detect movement of about 0.2mm is this realistic?
> > Cheers Rich
> >
> 
> Accelerometers are typically dynamic "sensing devices".  They sense
> "change" and are not a good choice for your electronic protractor
> device.  A cheap way to go is to use a resistive potentiometer ( a
> simple POT ) with a weighted pendulum.  A more sophisticated method 
of
> measuring the tilt angle you desire is to use an optical encoder 
who's
> shaft has a pendulum with a mass at the end. You could get "uber"
> fancy with gyroscopes and such, if you wanted to make a real science
> project out of it.
> 
> M5
>
I am working with a 3 axis device. resolution may be a problem since 
there is alot of noise but it is based on gravity. rotary encoders 
would be better.

brian