Recently I’ve been doing an Internet of Things project with energy harvesting, and this brings some unique challenges for the power profiling. Namely I have these requirements:
- The profiler must be able to measure typical li-ion battery voltage range, from 3.0 V to 4.2 V.
- The profiler must be able to measure bidirectional current, both charging and discharging the battery
- The profiler must have high enough current capacity for a wide area radio transmission bursts
- The profiler must be able to accurately measure currents down to microampere range.
- The profiler must be fast enough to measure current spikes of under a millisecond, for example Bluetooth Low Energy advertisements.
Neither Nordic kit or uCurrent fill these requirements: Nordic kit doesn’t have high enough voltage or current range, and uCurrent in combination with my oscilloscope forces a decision between milliampere and microampere range.
As the profiler is made for this sort of measurements, we’ll give it a try.
Unboxing the profiler
Buying the profiler went smoothly, DHL delivered the package within a few days. Always remember to account for customs fees and taxes, for example in Finland there is a 24 % VAT.
Software installation was a bit complicated. First, the Windows Defender warns about the installer possibly being malicious, maybe the installer image should be certified with Microsoft somehow? Second, the program requires license files which come with attached USB stick. Maybe this is to protect the profiler against cloners, but it still feels a bit strange to install licenses on a program which is distributed free.
The software itself is straightforward to use on 1.3.0, just click “Connect” and wait for the warm-up counter to count down to zero.
On the calibration the program asks user to connect GND and BATT. I assume the software nulls any offsets at this point. Note that this means connecting the battery to system without load, not shorting anything. After the calibration has run, the load can be connected and profile of the device measured.
There are some differences in the results between Nordic power profiler and ZS-2102, Nordic profiler reports higher peaks and lower average consumption.
The higher peaks can be seen visually in the Nordic Profiler data, maybe they’re glitches in the profiler or maybe a sensor turn on happened to match exactly a BLE transmission. Difference in averages is within the specified accuracy of the meters and might be because of longer wires with higher resistance with the ZS-2102.
Profiling the harvester
Next we can get into where ZS-2102 shines: Profiling energy harvesting system. We add a energy harvesting circuit in parallel with the load, and let’s see how the total energy consumption looks like.
As the profiler software is Windows-only and my laptop has OSX, I’m bound to my office which doesn’t get direct sunlight but has a Windows 10 PC. It’s comfortable for working but inconvenient for profiling solar harvester. In any case, a bright LED can pump out enough light to get good results.
One feature which I would like to have is fast voltage sampling, voltage is sampled at 50 ms interval and hardware is capable of 10 ms sampling. This means that transient events, such as voltage droops on radio activity are not seen on the voltage graph. On the other hand such transients should be measured with an oscilloscope anyway to avoid disturbing the power delivery with series resistor and extra length of wires.
While the ZS-2102 advertises profiling times limited only by the hard disk space, the hard disk space fills quickly. In the above series 80 second data was 613 MB, capturing a week of data is not really feasible with the kind of hardware I have at the office.
The ZS-2102 is a great tool for measuring power profile of battery-driven IoT devices, and it’s hard to match the current price of 699 USD for equivalent features.
- The profiler has good voltage and current ranges as well as accuracy for IOT devices.
- Bidirectional currents can be measured.
- Current sampling rate is fast enough for any reasonable power profiling at 1 MHz.
- The profiler is easy to use in most cases, just tap between battery and load.
- Profiler is physically small enough to fit in a small drawer of the lab when not used.
- It’s easy to take even long profiles as long as there is disk space available
- There is no input protection against accidental shorting of battery to ground.
- Voltage is sampled only at 20 Hz, which might miss voltage transients
- Long profiles consume a lot of disk space.
- GUI software is Windows-only, but Mac and Linux support are on a roadmap.
I’ll hope that the profiler will last me as long as my uCurrent did, ironically my uCurrent was destroyed when I accidentally shorted the current measurement across a battery. If you want to have one, head over to the Angler Circuits shop.
I received a greatly discounted profiler for this review.