Lpc2000

At 08:13 PM 3/15/2006 +0000, dijucthat wrote:
>Thanks for the replies! I think maybe I should have worded Q3
>differently.  What I meant was using an op-amp as an attenuator with
>gain = (less than one). The sensor maxes out at ~4.9v.It seems that
>a resistor attenuator (as suggested by Kurt) should work as well.
>(If the input impedance is sufficient) But I see what you are saying
>about the temp.  One of the sensors is a temp compensated absolute
>press sensor and it would be a shame to lose accuracy in the
>conversion.

Don't get too hung up over the temperature variation on the resistors, even 
at 50ppm/K over 100C range is 5 parts per 1000 or about 5 A/D 
counts.  That's for a fairly standard 1% 0805 resistor, precision resistors 
are likely to be better.  And of course if you are not running over such a 
broad range...

It shouldn't be hard to get down to a few counts.  And if your A/D is in a 
room temperature environment you probably can get down to less than a count 
w/o specifying anything other than standard resistors.

Even temperature compensated is your pressure sensor that good?

All that's assuming that the A/D is stable and accurate to less than a bit 
over temperature and that your input signal has less than 3mV worth of 
inaccuracy.  Check the A/D specifications, I think you'll find that it 
doesn't take a vary special resistor to get a signal source as accurate as 
the A/D.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
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