Home built uCurrent trouble shooting.

[ja421]

My uCurrent died (I think from over taxing it) -- I emailed Dave & got some tips on what to look at it, and replaced those parts - it was still dead so I decided to build my own (using his board & parts list)  (FWIW: the original unit read 2.5volts on nAmp range -- I replaced a resistor & both max4239's)

Testing went well for mAmp & uAmp testing -- however, nAmp; w/o anything attached/connected - it shows a voltage (between 8 and 12 mv);  I hooked it up to a cheap oscilloscope & it showed some volts (as expected) but as I put my finger close to (but not touching) the current-input posts, the reading fluctuated, a lot.  (I also list the parts I varied from, or had to pick myself)

The uCurrent seems to work properly otherwise, but having a reading w/ nothing connected is a little disheartening.  If I short the posts, it reads zero as expected. (Shorting with either the switch set to short or using a wire)  Unshorting causes the volts to jump back up. 

The voltage generally is around 10mv and goes up / down from there.

Any suggestions/thoughts on what might be wrong?
Thanks.

[JDW]

It's been 10 months since your post.  Did you ever fix the problem?

[ja421]

Sadly, no.   I suspect there are deviations in the parts that need to be accounted for... but what I don't know.

[guenthert]

Any suggestions/thoughts on what might be wrong?
Thanks.

EMI.  Put the uCurrent in a shielded enclosure, connect that to ground and repeat the test.

[ja421]

Tried that... Went so far as to use only battery powered & went outside away from all A/C power influences and ground the box to earth...