Re: Alarm delay in car?

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#133

From: Terry Pinnell
Date: Thu, 22 Aug 2002 06:25

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DaveC <anon@example.net> wrote:

>"This circuit will work with "idiot light" sensors (thermal and pressure 
>switches) on my truck. But what changes should be made to accomodate the 
>temperature gauge (analog sensor -- reduces resistance to ground as temp 
>increases) in my car? "

Please restate/clarify overall requirement. In particular
1. Names and action of of each digital sensor. I think there are two:
thermal switch and pressure switch, yes? And do they go low or high at
their respective built-in trigger points? Presumably that coincides
with their lights appearing in dash?

2. Is there just one additional analog sensor, namely the 'temperature
guage'?

3. What connection have you accessed to this, and what outputs do you
measure with a DMM? I gather that it's a resistance, but what range is
output from cold to max?

4. Do you propose to define an arbitary trigger value for this?

5. Do you want all three to contribute to an OR-type alarm as I
described?

>> If instead you want to set your own limits, and you can get access to
>> a varying output voltage from each sensor, then you need to insert a
>> simple comparator ahead of each.
>
>Can you be more specific (for someone not familiar with such details)? "Ahead 
>of each" - each what? What does a comparator circuit consist of? How is it 
>connected?

I had in mind a simple opamp comparator between each analog input,
with its defined trigger level as the reference, and its output going
to a logic citcuit such as the one I posted. If I'm right in #2 above,
then just one would be needed.

Terry Pinnell
Hobbyist, West Sussex, UK

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From: Terry Pinnell <terrypin@dial.pipex.com>
Newsgroups: sci.electronics.basics,sci.electronics.design,alt.engineering.electrical,aus.electronics
Subject: Re: Alarm delay in car?
Date: Thu, 22 Aug 2002 07:25:39 +0100
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