I've used the MAX472 and MAX471 chips with great success. These parts provide
current to voltage translation, and are perfect for high-side current measuring.
The MAX472 is intended for higher current applications using an external sense
resistor, while the MAX471 has a built-in sense resistor. Maxim's web page is at:
http://www.maxim-ic.com/

And the MAX471/MAX472 data sheet is at:
http://209.1.238.250/arpdf/1108.pdf

The MAX471 has a limit of 3A. Do not try to exceed this limit because the internal
sense resistor will fail. I know this from experience. Use the MAX472 with an
external sense resistor if there is any chance the current will exceed 3A, such as
inrush when power is applied.

To measure current using one of these, simply connect the output of the Maxim part
to an analog input on the PIC. (You do need an output resistor as described in the
datasheet, also add a 0.01uF cap across the output resistor to filter any hi freq
noise)  Do the A/D conversion, and you have your current measurement. The only
limitation is the resolution of the PIC A/D. If you configure the MAX472 to output
1V/1A, and select internal reference for the PIC A/D, the resolution will be
19.53mA/step. The resolution can be much better when using an external reference.
Check out the PIC datasheets about using the sleep mode to achieve better A/D
accuracy. It makes a significant difference in most cases.

Dave Sorlien

Ricardo Ponte G wrote:

>         Hi everybody,
>
>         I«d like to know if somebody can help me out with it:
>
>         I got to measure current controled with the 16C715 PIC, the range: the
> minimum as possible to 2 or 3   AMPs.
>
>         What method is apropiate ?
>
>         Some of you have an explanation sheet with the theory ?
>
>         Some schematic ?
>
>                 Thanks to all of you for the time...