[sdiy] frequency counter

[harrybissell]

I'd like to point out that tuning a VCO could also be done with a square
wave reference and a 'beat frequency indicator' which could be made
with an up-down counter method.   If you then took an x-or gate and looked
at a lpf voltage output (like with an LED) you could probably get even closer.

This would be a lot easier than a frequency counter built in a VCO...

H^) harry

James Patchell wrote:

> I have been working off and on to build something to characterize
> VCO's...trouble is, I have not given it too much priority.  And it wouldn't
> be a frequency counter...more like a virtual strobe tuner...(I know, there
> are tons out there you can buy)...but my instrument would include a MIDI
> interface, and a DAC output and would enable my to write a program that
> runs on my PC to automate measuring the VCO tracking, of every note.  Right
> now, I generally just check OCTAVEs, usually C1, C2, C3, C4, C5, C6 and
> C7.  It is time consuming enough just to do that (I do it more than once to
> make sure I took correct readings the first time....repeatability in
> measurements in very important).  But, alas, it may be some time before I
> get around to doing this....I was even thinking of scrapping what I am
> doing right now an implementing it in a Spartan 3....but...nah....
>
> At 12:29 PM 6/27/2004 +0000, harrybissell wrote:
> >Ian Fritz wrote:
> >
> > > I won't argue with you, but could you just say what is wrong with using a
> > > counter?  It's what I've always used, and it certainly *seems* to work.  In
> > > what sense doesn't it work?
> > >
> > >
> >
> >I'm one of those who question the usefulness of the frequency counter. I use
> >a musical tuner, sine wave generator, scope (lissajous)... and my ears as
> >a final
> >
> >QC check.
> >
> >I set the sine wave generator to a midrange reference frequency. Use the
> >Tuner to
> >check
> >the reference... then use the lissajous patterns to take it from there.  The
> >lissajous patterns
> >are very similar to a strobe tuner... it is a matter of pattern
> >recognition from
> >then on.
> >
> >I think that freq counters are too hard to intrepret (sure they're OK for
> >A=440).
> >And too
> >slow to settle to reasonable precision.
> >
> >oh... and mine is broken :^P
> >
> >I would like a frequency counter to determine the linearity of an unknown VCO
> >design... lissajous
> >patterns don't help much.
> >
> >H^) harry
>
>          -Jim
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> http://www.oldcrows.net/~patchell
>
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