Need a Comparator that will ignore glitches

manaboutdog

Hi All,

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.

M

DublinDilbert

To be honest, if you can do it in software, with say an exponential filter i would do it, as it's much easier to modify, and deal with start up conditions than an analog circuit.

Also in an analog circuit when you need a long time constant you genrally need a large capacitor and resistor to achieve the time constant and it's not very flexible. I'm sure a 555 timer could be use to do what you want, as it's effectivly a voltage refferance / comparitor and flip-flop all in the one package, haven't used one in years, but a quick google would give alot of information:-
http://www.technologystudent.com/elec1/5554.htm
http://www.doctronics.co.uk/555.htm
http://www.kpsec.freeuk.com/555timer.htm
http://www.eleinmec.com/article.asp?4

Michael Collins

Yep, if you need an accurate timing an RC circuit wouldn't really be up to that. But a microcontroller would do the job nicely if it was clocked to an accurate reference like a quartz crystal. What's the purpose of it if I might ask?