Lpc2000

At 09:28 PM 11/22/04 +0000, you wrote:


>Hi,
>
>Im using the onboard ADC for a project I am working on. However I
>seem to be getting some strange values and it isnt acting as I
>expect it to.
>
>Two things mainly:
>
>One, when I take a voltage input of a constant voltage (0.5 * 3.3V)
>I get fluctuating values from the ADC which I output to
>hyperterminal. This is very strange as they should be all the same
>value.

How much are they fluctuating?  I'd expect some fluctuation.  Also what 
does your signal look line on an oscilloscope (AC coupled at about 5mV/div)?


>Two, when I take the value from ADDR I place it into an int. However
>I am saving these values into an 8-bit value array so I have to
>shift right twice (due to the ADC being 10-bit). Or so I thought.
>The values I get from this array seem to be about right, but the
>resolution is in steps of 8 or 16 not the expected 1. This is no
>good for my application. I have also tried dividing by 4, but this
>produces even stranger results!

Have you compared before and after values?  If the division is not tracking 
the input values it's probably just a simple arithmetic error.

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