On Mon, 21 Aug 2000, Andrew Kunz wrote:

> Scott,
>
> According to that last posting about the sine wave generation (not about
> determinism <G>), it appears to me that you are expecting to see a sine wave as
> an input.  I'm not so lucky - I just get a 60uS pulse during the zero crossing,
> as determined by some off-chip electronics.
>
> Do I want to implement a FIR filter and try to track either 50 or 60 Hz (yes,
> it's supposed to lock to either one) with a PID loop? Guess I got a little
> confused - that was basically my thought.
>
> As for amplitude, I only have to generate a 0-5V sine wave at the right
> frequency (determined by the incoming line);  the power electronics convert that
> to 480V for me.

Oh.

You're correct. I was assuming that you had continuous access to the sine wave.
I guess it's safe to assume then that the `off-chip electronics' do some kind of
conditioning to guard against the noise problems I alluded to before. I haven't
thought about the problem in this context, but it'd probably make sense to
create a filter that takes the time between pulses as it's input. This filter
could be as simple as averaging the last n-samples. The output of the filter
would be the period of the sinewave. Divide this by `N' and you'll have the sine
wave sample time (and could be fed right into the phase accumulator sine wave
algorithm - btw, I think you'll want to use this algorithm [or at least a
variation], otherwise there will be jitter if N doesn't exactly divide into
period of the sine wave).

What does the synthesized sine wave need to lock to? Is it sufficient to
generate the right frequency?


Scott

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