I have done sort of this before. I had a shaft encoder giving to few pulses
out, so the plan was to multiply the incoming A and B pulses by some factor.
I measured the width of the incoming pulse, divided the time into the
multiplying factor and outputed the needed amount of pulses with the width
proportional to the incoming pulse. Everything worked fine for more or less
steady rotation of the shaft (approximately constant frequency). When the
shaft was accelerating fast or breaking fast everything was wrong, the unit
started to drop pulses for obvious reasons. So I'm very interested to hear
if everyone has a better idea of how to do this but with changing
frequencies at a fast rate.
best regards
RA
----- Original Message -----
From: "Picdude" <picdude@NARWANI.ORG>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, April 24, 2003 7:02 AM
Subject: Re: [PIC]: Frequency multiplier?


> Since you put this as the [PIC] topic, I'm going to invent a PIC solution
for
> this, which I haven't tried, but thinking should be doable...
>
> Measure the low-time and high-time of the first pulse, then generate
pulses at
> 130% the frequency of that ..... repeatedly in a loop.  While that's
> happening, in a sort of feedback mechanism, count both input and output
> pulses and adjust accordingly by offsetting the next pulse(s).
>
> This method should provide low jitter, but would add a small (approx 1/2
to
> 1-pulse) delay from input to output, and depending on the actual coding,
may
> introduce a limitation on how fast the output will follow the input on
freq
> change.
>
> Of course this is not totally trivial, but it should be doable with any
simple
> PIC.
>
> Cheers,
> -Neil.
>
>
>
>
>
>
> On Wednesday 23 April 2003 20:08, Gary Neal wrote:
> > Hi,
> >
> > I've got a variable frequency signal (200hz to 4khz) whose frequency I
want
> > to increase by 30% (5v signal).  IE if the input frequency is 1000hz, I
> > want to output 1300hz.  Is there an easy method of doing this?  I've
heard
> > of PLL, but don't have a clue how to build them, so if there's an easier
> > option that would be great.
> >
> > Thanks,
> >
> > Gary
>
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