Re: Trigger on variation of an analog signal

From: Tim Wescott (tim_at_wescottnospamdesign.com)
Date: 06/29/04 

Date: Tue, 29 Jun 2004 11:41:45 -0700

pozz wrote:

> Hi all,
>
> I have an analog signal (0-5v) that is normally stable or slowly
> changing. I want to design a simple circuit (analog and digital)
> that triggers a line when a strong variation occurs in a period
> of time.
> For example, if in 10 minutes the signal change from 3V to 1V,
> than a signal must be raised from 0 to 1 in order to wake-up a
> microcontroller. After doing its work, micro untriggers the digital
> signal and goes in sleep mode again.
>
> It's important to trigger a digital line on a strong variation on
> an analog signal. I can do that with micro and internal ADC, but I
> want it in sleep mode.
>
>

You really need to define what you mean.

Do you mean if the signal varies by a certain amount in a certain time,
or do you mean if the signal just moves by a certain amount in _any_
amount of time? The first requires a differentiator that needs to
remember things for minutes at a time; this may be easiest to implement
with your microprosessor. For the second you could set a a window with
a pair of DACs and use a pair of comparators to monitor the signal. 

-- 
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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