Measuring current consumption


#1

This is somewhat off topic, but since there are multiple related discussions going on I thought I’d ask it. For those of you measuring power consumption on your devices in awake and sleep modes, how are you measuring? I would like to do the same in order to calculate and optimize battery life.

I have an oscilloscope (Rigol DS1104Z Plus) but to be honest haven’t really learned how to use it yet. I don’t need ultra-precise measurement, but rather a general idea of the current my carrier board and the Boron LTE are using over time.

Any tips the community can provide are very welcome (especially tutorial video links!). Thanks in advance.


#2

If you want to do it accurately, I suggest externally measuring the voltage drop across a precision resistor (0.1% or better.) Selecting the resistor value can take some thought - at max current draw (e.g. cellular tx), you want the voltage drop to be low enough that the device does not brown-out, while at min current draw (e.g. sleep), you want the voltage drop to be large enough that you can still measure it accurately.

I have found that using a low resistance, and using a x100 instrumentation amplifier can give very good results - you can measure the raw voltage drop for the large current excursions, and the x100 value for the low current periods.

You can use the capture capability of an oscilloscope to record the voltage drop(s) against time, and easily calculate the area under the curve, which is the energy used. Don’t forget to also track the supply voltage over time. Converting the data collected into coulombs is the best way to calculate and predict battery life, in my experience.

There are other methods you can use, such as hall-effect sensors (which have the advantage of negligible voltage drop) but frequency response and dynamic range need to be considered carefully.


#3

Check this post @Rftop has a great suggestion


#4

Both are great suggestions. Thanks for the tips.


#5

@picsil, besides a high quality bench multimeter, I also use a uCurrent Gold which basically implements what @AndyW describes. By attaching it to a multimeter, you can measure very low currents without any burden voltage, ie impact to the circuit you are measuring. Hooking it up to an oscilloscope allows you to measure the current consumption in real-time an characterize dynamic vs static current.

One note if you get one of these, the button cells don’t last very long so there is enough room in the case to wire up a 2xAAA battery holder, giving a much longer run time.


#6

+1 for the µCurrent Gold. It’s what I use for measuring Sleep Current.

I’ve been looking at this lil guy lately:
https://lowpowerlab.com/guide/currentranger/
image


#7

Looks like this is currently unavailable, though it looks good. I realized after your post I had already looked at some videos on it.


#8

The current ranger looks nice! Love the built in LCD display eliminating the need for a external multi-meter.


#9

@RWB, and it has a Bluetooth option… for wireless data logging.


#10

SOLD :smile:


#11

Gotta get me one of those!


#12

Nordic has a power profile kit you might find useful…

I also use a Keil Ulinkplus to measure power consumption aligned with code execution.