

Case study: measuring power consumption of wireless systems (iCub robot) - swamp40
http://community.arm.com/groups/embedded/blog/2015/01/13/case-study-measuring-power-consumption-of-wireless-systems-icub-robot

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swamp40
The widely varying current needs of microcontrollers as they transition from
wake to sleep and back again can be difficult to estimate accurately.

Here is a simple trick we use to measure _average_ current consumption on our
battery powered microcontroller designs.

(It's an important number, because that's what tells you how long your
batteries will last.)

We replace the batteries with a huge capacitor, like 10,000uF or 20,000uF
(whatever it takes to give you a few minutes of run time).

We charge up the capacitor with a variable power supply to the high end of the
battery voltage, then we start a stopwatch and disconnect the variable power
supply.

We watch the voltage drop to the typical minimum battery voltage, and then
stop the stopwatch.

Then we remove our board, replace it with a variable resistor decade box, and
repeat the experiment.

We repeat that, adjusting the resistor box until we find the exact resistance
that discharges that huge capacitor in the same amount of time as our board.

(We measure the resistance of the box at the end with an ohmmeter, because
they are always off a bit.)

Then we use that resistance (and the mid-value of the voltage drop) to
calculate the average current drain of our board.

