HardySpicer wrote:
> On Oct 10, 4:19 pm, "Manfred" <mmorn...@[EMAIL PROTECTED]
> wrote:
>> Hi all!
>>
>> Maybe someone here might help me with a DSP problem that should be
>> trivial, but to me, as a newbie to DSP, is not.
>>
>> I'm developing a microcontroller-based speed controller for my small
>> hydroelectric plant. I'm using a PIC 16F628 for this. I'm detecting the
>> zero crossings of the 50Hz signal coming from the generator, and
measuring
>> the duration of each half cycle, obtaining a signal at a rate of 100
>> samples per second. The signal is in 16 bit format, and nominally 10000
>> counts tall. Typical variations are a few tens of counts, and
occasionally
>> as much as 1000 counts. I'm subtracting the 10000 reference, and using
the
>> resulting error signal as input to a pro****tional-integral control
>> function, whose output drives dump loads that burn off the excess
output
>> from the generator.
>>
>> The little problem I have is that a small 420Hz signal on the power
line,
>> apparently coming from the generator's internal voltage regulator, is
>> causing jitter in the zero crossings, which is in turn causing the
>> pro****tional function of my controller to imprint an unwanted
modulation on
>> its output. So I would like to apply a low pass filter function to my
>> signal, with a cutoff frequency of roughly 20Hz, before the P-I
function.
>>
>> The question is: How can I implement this DSP low pass filter? It has
to
>> be in some simple way, because neither the PIC nor I can handle overly
>> complex math!
>>
>> The only thing I can come up with is averaging the last several
samples,
>> perhaps with some weighing. But there must be some better method!
>>
>> It is desirable that the time delay in the filter be as short as
>> possible.
>>
>> I would be most grateful for any help in this, be it with an
explanation
>> of how to implement the filter, or a hint as to where I can find this.
>>
>> Manfred Mornhinweghttp://ludens.cl
>
> Yes - it's called a resistor and a capacitor. Put the capacitor to
> ground and the resistor in series. Voila and no programming - now
> that's such a great discovery that two components can do better than a
> pic.
One of us doesn't understand his approach. I think that he counts some
high-frequency oscillator during the interval between zero crossings to
determine the period of his waveform, the result of each measurement
being a number; a bunch of bits. Where should the capacitor go?
Jerry
--
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