All you may need is a voltage divider using 1% precision metal-film
resistors. I've been buying these from my local Active dealer - I use a
digital voltmeter on the ohms scale to match resistor values to 0.1% or so.

The temperature drift of these is certainly less than the 0.1% resolution
you get from the A/D converter in the PIC, so I wouldn't worry about it. If
you can find a source for 0.1% or even 0.01% wire wound resistors, even better!

How simple you can make the divider really depends on the accelerometer
output - what kind of a load can it drive. If it can drive a 1kohm load,
then you could use low value resistors for a divider, and the input
resistance of the PIC would not have any effect. If you need to use 100k
resistors, then you have a problem. But the problem is easily solved by
using an operational amplifier (op-amp) buffer between the accelerometer
and the voltage divider - the op-amp presents a very high resistance to the
accelerometer, and is capable of driving a low resistance divider.

Op-amps a cheap and easy to use.

Head off to your library and borrow a copy of "The Art of Electronics" by
Horowitz and Hill, and read up on op-amps (and everything else, if you have
time!)

Larry

At 10:05 PM 11/7/2002 -0500, you wrote:
>I am a student using a PIC 16F877 in a project and would like to read an
>analog input from an accelerometer setup that varies its output from 0-11v.
>This voltage is put out by a signal conditioner made by the manufacturer of
>the accelerometer so I have little control over it. Now I know there are
>vref pins I can use, but some analog inputs will be in the 0-5v range and
>I'd rather not lose precision on them by changing the voltage reference to
>accomodate the range of the accelerometer. How can I step down the 0-11v to
>0-5v? Can I use two high high value resistors to divide the voltage down? I
>am considering that approach but am afraid of the effects temperature will
>have on the resistors and thus the readings, since I am told that resistors
>are prone to drift with temperature. The accelerometer will be used
>outdoors, inside a model airplane, where temperature could vary
>considerably. Also, having little background on EE, I am not sure what other
>effects might follow from using the resistors. Any thoughts or other
>approaches? I know little about EE, so bear with me if this is too basic.
>Thanks.
>
>Lindsay
>
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Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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