I have a micro which I want to measure the 'deep sleep' current, but my meters are not up to the job. I have a Fluke 115 (I think that's the number), but its not a good meter for this. I also have some cheap meters that have a 4ma range, but do not seem to be very accurate.
So I take a 100K resistor, put it in-line with the battery (lion- ~4.1v when charged), and also put a jumper across the resistor. I power up the micro, put it in deep sleep, remove the jumper, and measure the voltage across the resistor. I show 0.84v volts across the resistor. I then put the jumper back on, wake the micro to prove it was actually in deep sleep, and not powered down. (Power goes to a mcp1700 3.3 regulator, so I'm measuring that, too).
If I calculate correctly, an 0.84v drop across a 100k resistor means there is 8.4uA of current flowing through it. Is this a good way measure low currents when the meter can't handle it? (the cheap meter was showing ~200uA)
I don't have to run years from the battery, so would be thrilled if this amount of current is close to the actual value. I can also do some tweaking if this method is half-way reliable.