ADC current readings while powered by USB

[oslinux]

Hi all!
I've got a problem measuring a DC current from a 15V 0~2A generator.

I'm using an USB-powered PIC18F2553 and i should place a shunt resistor in series between the generator and measure the voltage drop across the shunt BUT i can't connect the ground of the pic to the shunt cause the USB and the generator shares the same ground.

Now, have you got any solution?
Considering that i cannot use an hall effect sensor because it's not enough sensible (I need to measure milliamperes) and it might be placed near magnetic fields which affects the reading.

Thank you.
Luca

 

[kender]

Hi Luca,

The chip, which you're probably looking for, is called High Side Current Sense Amplifier. For an example, see LT6106 made by Linear Technology. There are others made by Maxim, Zetex and others.

By the way, Hall effect and magneto-resistive current sensors ICs are usually shielded from external magnetic fields well.

Best,
- Nick