The well-engineered µCurrent
Dave specs the thing with a 2-KHz bandwidth, but I found it gave reasonable results out to 3.5 KHz. This is definitely not something to track power consumption of your system on an instruction-by-instruction basis. Or to watch current zoom up when the CPU wakes up for a hundred microseconds. But it's great for understanding static and more slowly-moving events.
Click on image to enlarge.
Bottom trace:3.5 KHz input to the µCurrent (through a 10K resistor).
Top: output from the µCurrent, 200 µsec/div.
Dave has a full write-up including a schematic about the µCurrent here: www.alternatezone.com/electronics/ucurrent/uCurrentArticle.pdf.
The unit is available for $60 from AdaFruit. Definitely recommended for those who need to make low-current measurements.
(If you need measurements in the femtoamp range, check out this from Bob Pease. A picture is here. For mind-boggling measurements at attoamp levels--6 electrons per second--see www.keithley.com/data?asset=50390).
Jack G. Ganssle is a lecturer and consultant on embedded development issues. He conducts seminars on embedded systems and helps companies with their embedded challenges, and works as an expert witness on embedded issues. Contact him at jack@ganssle.com. His website is www.ganssle.com.
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