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From: Spehro Pefhany
Subject: Re: Pulse Height Measurement
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
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Date: Tue, 21 Jan 2003 17:41:30 GMT
NNTP-Posting-Date: Tue, 21 Jan 2003 12:41:30 EST
On Tue, 21 Jan 2003 17:06:25 +0000, the renowned Don Pearce
>Are you really trying to measure the peak - even if it occupies just
>one sample? If not, perhaps you would do better with a sort of rolling
>average that smooths off some of the noise. This would actually be a
>lowpass rather than highpass function. But it would give you smoother
>and more reliable data to measure.
Seems to me that he wants to measure the difference between the
signal and the signal passed through a LPF, assert an interrupt on
differences that exceed a +/- threshold from that. Pretty
straightforward, a difference amp or in-amp and 2 comparators, plus a
DAC and gain-of-minus-one amplifier to get -DAC.
He wants to detect the peak(ish) bits of +/- signal, so that's the
only tricky bit. Perhaps a pair of the classic precision rectifier
circuits with caps on the outputs. Then have the micro check
that the pulse isn't there anymore (if necessary) and reset the
caps (TGs across the diodes) after grabbing the reading, then
re-enable interrupts and go back to whatever it was up to.
Seems easy enough. Have to keep the sample cap reasonably
small for it to be able to follow fast enough, maybe <= 0.01uF.
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