Aaron Hickman <Aaron.Hickman@drexel.edu> wrote:

> Thanks for the quick reply!  Unfortunately, I need to display
> voltage to the nearest mV (ie. 3 decimal places).  Can your
> previous method be adjusted to do this?

Hi, Aaron.

The easiest way to get mV precision is:

    1.  Find the absolute value, as I suggested.  This will give you
        a number in the range [0-32767].

    2.  Shift it left one position (multiplying it by 2), so Step 4
        will be easy.

    3.  Multiply it by 10000 using your choice of 16-bit x 16-bit
        multiplication routines.  You'll get a 32-bit result.

    4.  Divide the result by 65536.  This is REAL easy; just discard
        the least-significant two bytes from the 4-byte result of
        Step 3.

    5.  You now have abs(ADC) * 10000/32768.  Convert it to whatever
        format your display wants, put a decimal point between the
        third and 4th least-significant digits, and set the sign to
        the sign of your original number.

-Andy

P.S.  I'm copying this to the PICLIST.

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499