Re: Need a Comparator that will ignore glitches

pfitz wrote:
I need a comparator that will monitor a voltage level for me and trigger
when it stays above the threshold for a set period of time eg 100ms. Any
spikes above the threshold which do not exceed this period should be
ignored? I can possibly do this with software in the current project but, if
I could get a quick HW solution that would be a lot better.

Any suggestions on a simple way to do this in HW?

Where is the spike? What does it look like? You can either filter the
input(s) to the comparator, or you can filter the output.

Filtering the output would probably be done based solely on time
criteria (like you said). A retriggerable one-shot will do it in
hardware nicely. There are also shift-register/counter based debouncing
chips in old catalogs (e.g. MC14490).

Also there are power-on-reset chips (maybe under "supervisory power" in
the catalogs) that incorporate all of a reference voltage, a
comparator, one or two time constants, output drivers, sometimes output
switching, etc. TL7700 series is somewhat fundamental and Maxim others
have some pretty fantastic riffs on the theme.

Filtering the input(s) is based on more of RC time constants, and might
be set up so that the time delay for a large deviation is small, but
the time delay for a small deviation is long.

Tim.

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