Ira,
My program is currently running in user space, and as the intention
is to heve custom FPGA module, I've simply cross-referenced the
velocity output from the quadrature to the speed the motor was
commanded to spin at...
I'm looking for changes in value rather than absolute values. I use a
couple of simple averaging techniques to generate a smooth velocity
trace - but I have the advantage of a lot more pulses per revolution.
If you don't need the video you can create a custom FPGA application
using the template Jesse Off placed on opencores.org. But my
application needs the second SD card and Video, so paying Technologic
Systems to produce the additional functionality is an economical way
to go.
It should be easy to implement a X4 counter rather than the X1
counter, but the X1 has the advantage of having less noise induced
jitter. I'm probably going to spec selectable X1 and X4 modes for the
custom FPGA to investigate which gives the best results.
I found an interesting webpage relating to quadrature and velocity at:
http://zone.ni.com/devzone/conceptd.nsf/webmain/
492D39D15D27C5DF86256F3B004B9C1D
Regards,
PJE
--- In "drrock77" <> wrote:
>
> PJE,
>
> Thanks for the info. I'd be really curious about using the x4
> counting, I'd be interested in learning how one would modify the
FPGA
> to accomodate this.
>
> I've been using a similar approach for calculating the velocity. I'm
> using the TC4 debug 4-bit timer as well. 983.04 kHz is what I read
as
> well. Unfortunately, I am not calculating RPM's correctly using this
> appraoch. At least I this is what I think. I am verifying my
> calculated velocity by measuring rotation with a non-contact optical
> tachometer. Unfortunately, our encoder onlyhas 64 ticks per rev and
> this is challenging to accurately calculate a velocity from.
>
> Did you perform any verifications on the T4 clock to ensure that
your
> timings are accurate/consistent? Did you develop a kernel module or
> user space program to perform the velocity calculations.
>
> Our project is for a commercial application, so we may not be able
to
> use your code. I may be over simplifying thigs, but it should be
> fairly straightforward to go from a x1 counter to a x4 counter.
>
> -Ira.
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