AVR-Chat

> A idea on how to 
> measure current on high voltage systems is highly appreciated?

I agree with Roy, an isolation amplifier is perfect for this 
situation (Analog Devices AD202, Texas Inst. ISO124, or similar).

But, since the voltage is only 70VDC and not the hundreds of volts 
iso. amps. are often asked to deal with, check out a differential 
amplifier with a high common-mode voltage rating.  That way you can 
do your measurement with the sense resistor on the "high-side" and 
not be worried about the 70VDC.  Analog Devices has a bunch of diff. 
amps that would work well.

Or, simplest yet as Roy mentioned, put your sense resistor in the 
the low line (GND) before the line is terminated at the system 
ground.  If you can ensure that the polarity is never reversed, you 
will only have to read up to whatever the full-scale voltage is for 
the sense resistor....no high common mode voltages to deal with.

John