>
> I tired ADXL202 for accelerometer and tried to measure a short
> montion.
>
> I used capture mode and main cal are as below:
>
> ...
>   ccp2_2=cpp2_read();
>   //cal total and width
>    //65536*0.2us=13307.2us, is 13ms. for 20mhz crystal.
>   //65536*1us=65 ms. for 4mhz crystal
>   //keep every timer1_0->timer1_1 or timer1_1->t2 must <= than 65636.
>   //can have one roll over. timer1 continuously run without reset.
>   if (ccp2_2<=ccp2_1)ccp2_low_n=65536-(ccp2_1-ccp2_2);
>   else ccp2_low_n=ccp2_2-ccp2_1;
>   if (ccp2_1<=ccp2_0)ccp2_high_n=65536-(ccp2_0-ccp2_1);
>   else ccp2_high_n=ccp2_1-ccp2_0;
>   ccp2_0=ccp2_2;//cal end, give to _0 as next starting rise
> ...
>
> Above work perfect, but a value I get is too small comparing with
> g.

> -----Original Message-----
> From: pic microcontroller discussion list
> [.....PICLISTKILLspam@spam@MITVMA.MIT.EDU]On Behalf Of paul x
> Sent: Monday, 8 December 2003 12:34 PM
> To: PICLISTKILLspamMITVMA.MIT.EDU
> Subject: Re: [PIC]:ADXL202 Accelerometer. Size the hammer correctly.
>
>
> what I tried is to measure speed of moving object that driven by motor.
>
> acceleration, a is too small comaparing with gravity g. So, little tilte
> will
> become huge output of a. How can I canceal g from a, becomes critical!
> For proper cancealation of g from a, I need three axiles measurement and
> large amount of calculation.
>
> I have not try how to measure 3 acceleration by one pic,although I got
> quite good reading from one measurement, in a 1% range with 200
> sample rate
> and digital filter.
>
> is there any body succed in speed measurement of using adxl202? I
> never heard.
>
> Paul
>
>
> ----- Original Message -----
> From: "Robert Rolf" <.....Robert.RolfKILLspam.....UALBERTA.CA>
> To: <EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU>
> Sent: Sunday, December 07, 2003 12:36 AM
> Subject: Re: [PIC]:ADXL202 Accelerometer. Size the hammer correctly.
>
>
> > paul x wrote:
> > >
> > > I tired ADXL202 for accelerometer and tried to measure a short
> > > montion.
> > >
> > > I used capture mode and main cal are as below:
> > >
> > > ...
> > >   ccp2_2=cpp2_read();
> > >   //cal total and width
> > >    //65536*0.2us=13307.2us, is 13ms. for 20mhz crystal.
> > >   //65536*1us=65 ms. for 4mhz crystal
> > >   //keep every timer1_0->timer1_1 or timer1_1->t2 must <= than 65636.
> > >   //can have one roll over. timer1 continuously run without reset.
> > >   if (ccp2_2<=ccp2_1)ccp2_low_n=65536-(ccp2_1-ccp2_2);
> > >   else ccp2_low_n=ccp2_2-ccp2_1;
> > >   if (ccp2_1<=ccp2_0)ccp2_high_n=65536-(ccp2_0-ccp2_1);
> > >   else ccp2_high_n=ccp2_1-ccp2_0;
> > >   ccp2_0=ccp2_2;//cal end, give to _0 as next starting rise
> > > ...
> > >
> > > Above work perfect, but a value I get is too small comparing with
> > > g.
> >
> > Then it is obviously NOT perfect. Or rather, your design is flawed.
> >
> > > So, useless if I can't keep excuracy of leveling, that I really can't.
> > >
> > > My conclusion is ADXL202 only for static titling measurement.
> >
> > TOTALLY wrong conclusion. They -may- not work for -your- application,
> > but they DO work quite nicely when properly matched to the task,
> > and when properly 'adjusted'.
> >
> > I use a pair of ADXL202's for running limbs kinematic measurements.
> > (reconstructing limb position in 2D based on the tilt signal and
> > skeletal rules).
> > Accuracy is in the 0.5 degree range (better if we needed it).
> >
> > It's a matter of choosing appropriate geometry, PROPER filter values,
> > ADXL period, and Timr0 prescaler. And then some simple algebra to
> > extract the 'real' tilt info from the gross acceleration.
> >
> > We started out with the much less capable ADXL05s, and they work
> > too, although producing much higher noise.
> >
> > Unfortunately the solution is proprietary, but you're welcome to
> > work it out from first principles.
> >
> > Robert
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
> > piclist-unsubscribe-requestspam_OUTmitvma.mit.edu> > >
> >
>
> --
> http://www.piclist.com hint: To leave the PICList
> @spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu

> -----Original Message-----
> From: paul x [RemoveMEpaulxTakeThisOuTMAIL15.COM]
> Sent: 08 December 2003 02:34
> To: spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU
> Subject: Re: [PIC]:ADXL202 Accelerometer. Size the hammer correctly.
>
>
> what I tried is to measure speed of moving object that driven
> by motor.
>
> acceleration, a is too small comaparing with gravity g. So,
> little tilte
> will
> become huge output of a. How can I canceal g from a, becomes critical!
> For proper cancealation of g from a, I need three axiles
> measurement and
> large amount of calculation.
>
> I have not try how to measure 3 acceleration by one pic,although I got
> quite good reading from one measurement, in a 1% range with
> 200 sample rate
> and digital filter.
>
> is there any body succed in speed measurement of using adxl202? I
> never heard.
>
> Paul

>         Actually, to nitpick a little, gravity CAN be distinguished from
> acceleration. The reason is gravity changes with altitude, the farther
> you
> are from Earth's surface the less it's effects. Therefore, on a rocket
> traveling away from the earth the force of gravity at the tip will be
> slightly less then at the tail. Acceleration OTOH is consistent along the
> whole rocket. So it is theoretically possible to distinguish the two
> (using
> two sensors you can find the difference in the force on the rocket, using
> the rockets length and altitude you can figure out the force of gravity
> on
> it, and using that you could theoretically null the effects of gravity on
> your number).
>
>         Now, for reality, this effect is so small it takes VERY
> sensitive and VERY
> large instruments to detect. So it's pointless in the sort of app we'd
> all
> consider, nevertheless the difference IS there. I'm just in a nitpicking
> mood at the moment, forgive me! :) TTYL