Nordic Power Profiler Kit II

One of the most critical challenge of embedded systems is managing the power budget. And very often, measuring power consumption turns into another major challenge.

I have already reviewed proprietary solutions like EnergyTrace, albeit optimised for Texas Instruments silicon, and more general tools like the volt-amp-watt-meter based on the INA219.

Nordic comes with an interesting option: a universal ammeter with 8 logic inputs.

Hardware

The kit includes the ammeter in a translucid case, a 4-way cable and a 10-way cable.

The device features two USB ports: one for data and power, another for power only; a swtich button and a RGB LED whose colours are not documented.

Software

The installation of the software requires two steps:
Good point, the source code is open source and available at a GitHub repository. It is also platfrom agnostic and runs on Linux, Mac and Windows.

However, on Linux, the device was listed with lsusb but wasn't detected by the Power Profiler application. The documentation doesn't mention that Linux computers require an additional step:
  • Install the nrf-udev package, which contains udev rules for nRF development kits.

Usage

The ammeter operates in two different modes:
  • Source mode: The ammeter provides the power, limited to 600 mA;
  • Ampere mode: The ammeter measures the current, up to 1 A.

One the device has been selected and the mode set, the left pane offers other parameters, like the voltage to be supplied in source mode, the number of samples per second, up to 100 k, the duration, and the logic channels to monitor.
The RGB LED adapts its colour to the selected mode:
  • green: device connected:
  • red: source mode:
  • blue: ampere mode.

Surprisingly, the documentation doesn't mention the meaning of the different colours.
The ammeter records current in Ampere, time in seconds and electric charge in Coulomb. One Coulomb corresponds to one Ampere during one second.

To translate Coulomb into mWh, commonly used to rate the capacity of batteries, multiply the Coulomb by the voltage, and then by 3.6.
1 C Coulomb = 1 A Ampère × 1 s second
1 W Watt = 1 V Volt × 1 A Ampère
1 J Joule = 1 W Watt × 1 s second
1 J Joule = 1 V Volt × 1 A Ampère × 1 s second
1 J Joule = 1 V Volt × 1 C Coulomb
1 Wh Watt·hour = 3600 J Joule
1 mWh milliWatt·hour = 3.6 J Joule
1 mWh milliWatt·hour = 1 V Volt × 1 C Coulomb × 3.6
Additionally, the device can record up to 8 logic signals. This is a great way to identify parts of an application. Alas, there is no option to use those logic inputs as triggers, for example to start or stop the trace.

The connections are:
  • On the left, power: Vin and Vout with an external power supply, Vout in source mode, and ground.
  • On the right, input references for high and low signals, and 8 logic inputs.

In the example pictured, the device is configured on source mode and the USB cable supplies the power.
The Power Profiler application displays the recorded data with a very clear graphic. Data can also be exported as a CSV file, perfect for later analysis with a standard spreadsheet.

Data appears as rather noisy, and the application provides no filters.

Conclusion

At around EUR100, the Nordik Power Profiler II offers an insteresting solution for measuring power consumption of embedded systems.

The 8 logic inputs allow to set markers on the code to identify the specific parts of the applications under review.

The limitations I have experienced (incomplete procedure, lack of trigger feature) could be easily solved by updating the documentation and the software.

Pros

  • Platform agnostic application
  • Ease of use
  • Standard CSV output

Cons

  • Incomplete installation procedure for Linux
  • No trigger feature

Wrap-Up

  • Affordable solution
  • Intuitive software
  • Some features missing

Links
Posted: 15 Apr 2022
Updated: