Overview
Power consumption of embedded and IoT devices is getting reduced day by day. It is quite challenging to reduce the power consumption without measuring the dc current and energy properly generally done using power profilers.
Are DC current energy analyzers/power profilers available?
There are only a handful of devices available in the market which can help you easily analyze and estimate how much power embedded device is consuming at different stages of operations and over the period of time how much energy it is consuming.
This analysis becomes even more critical if you are building a device which will be powered by battery or will have some kind of power back up.
Traditional Way
Many of the engineers still uses the traditional approach of the series shunt resistor or multimeter based current measurement, which doesn’t gives accurate results. Why? because in a typical embedded system design, the current requirement changes from time to time at a very fast rate. It’s hard to measure those dynamic current.
If you don’t have a very fast sampling frequency high precision DC current meter with PC interface and custom software, it will be very hard to do the analysis.
Even if you could do that, you will need voltage measurement and then energy calculation for each measurement. Ideally you need a measurement device with can give you atleast voltage, current, and computed energy readings on a running graph plot. With the help of graph plot it will be much easier to understand how the current consumption of embedded product is changing based on state of it operation and then hardware and firmware engineers can optimize the power consumption.
New Approach in 2021
Fortunately, there are two companies who has designed such a product to help engineers
Let’s talk to about them one by one in some details.
1. Joulescope (~799$)
Joule scope measures current from nanoamps to amps while simultaneously measuring voltage, power, and energy.
Joulescope will connect your power supply in series to do all the measurements. It can operate in multimeter mode where you can see all measurement readings and in oscilloscope mode where you can see current graphs.
The instrument is powered by USB and transfers all the data to PC software via USB 2.0 high speed interface. The PC software comes along with the instrument.
Technical Specification
- -1V to 15V voltage range
- -1A to 3A current range, continuous (10A pulses)
- 1.5 nA resolution, equivalent to 32-bits of dynamic range
- 250 kHz bandwidth with 2 million samples per second, 14-bit, simultaneous current and voltage
- Rapid 1 μs switching between shunt resistors for seamless dynamic current measurement
- Computes power and total energy
- Sensor ports electrically isolated from USB
- Works with Microsoft® Windows®, Apple® Mac® OS X®, and Linux®
Current Accuracy
Voltage Accuracy
For more details, please read the user guide.
2. Otii Arc (~699$)
Otii Arc is truly versatile. It is a 2 quadrant source measure unit (SMU) with a constant voltage or constant current source and sink together with a high precision multichannel multimeter. Set it up as a constant, linear power supply or a battery of your choice (with Otii Battery Toolbox).
Use it as a power analyzer or profiler to record and display real-time currents, voltages and/or UART logs. It provides nA resolution current measurements with a sample rate of upto 4ksps.
Otii Arc measures 10,9cm x 14,4cm x 4,4cm (WxLxH) and weighs 450 grams and the PC software works on Linux, Mac and Windows platforms.
You can power it by USB for portability, or by using an external DC-adapter.
Voltage Accuracy
It can measure the voltage upto 5.0V(MAX) with an accuracy of ±(0.1% + 1.5 mV) with sampling rate of 1ksps.
Current Accuracy
Current Measurement(0 – 2.5A, 5.0A peak) Accuracy is ±(0.1% + 50 nA) for upto +-19mA, above that the accuracy is ±(0.1 % + 150 µA).
Please go through the technical spec carefully before taking a purchase decision.
3. Nordic Semiconductor Power Profiler Kit 2 (PPK2 – 89$)
4. NanoRanger by AltoNovus (£159.95 / ~ 220$)
NanoRanger is a 3.5 Digit DC current meter very useful to measure very low currents down to nano amps
With auto-ranging feature across nine range, it is able to measure currents anywhere from 800mA to 1nA, with a maximum resolution of 10pA 🙂
Burden drop is only 50mV for full range.
Display shows average, maximum, minimum current as well signal to noise ration which is very good for quick understand of power consumption.
NanoRanger current measurement tool could be used by engineers, makers who are interested in precise current measurements, specially who are building low power embedded products powered by batteries.
It has USB port for PC interface but lacks a software which can show readings, create graphs, generate reports, etc. This is a major downside of this current measurement tool.
Good thing is they keep updating their firmware and the latest one gives you ability to get 150 reading per second. You can build your own little software to plot the graphs.
You can download the latest firmware and read more about how to update the firmware.
5. Current Ranger by Low Power Lab (120$)
CurrentRanger is a nano amper current meter with an OLED display .It has auto-ranging and can measure current in both directions.
It has Bluetooth data logging option as well.
It is a highly configurable and affordable ultra low-burden-voltage ammeter, appropriate for hobby and professional use where capturing fast current transients and measurement precision are important. Mainly if you are building a low power embedded device using battery as power source.
Features:
- Low noise zero-offset with 3-ranges (1mV output per nA/µA/mA)
- Low input burden voltage, high precision & bandwidth analog outputs
- Increased flexibility and usability with several input and output terminal options
- Auto-ranging capable
- Use it as a standalone meter with a small OLED display or with a multimeter/oscilloscope
- Ultra fast range switching between any ranges (even nA to mA) without any glitching/bouncing of a mechanical switch
- Low Pass Filter mode – very useful to capture low noise signals on oscilloscopes
- Unidirectional mode – most used mode in measuring DC currents ranging from [0, 3.3A]
- Bidirectional mode – split supply biasing allows AC currents measurement ranging from [-1.65A, 1.65A]
- LiPo battery powered – long life and extended measurement range, auto-power-off
- Full digital control for power & range switching via touch pads
- Datalogging possible via Bluetooth serial module
- SAMD21 Cortex M0+ powered, change firmware to your needs
- Optional buzzer for audible feedback
I hope you have found this information useful.
6. ZS-2102-A IOT Power Profiler (649$)
7. Battlab One Battery Life Optimizer (99$)
8. Hardkernel SmartPower 3 (45$+ 9.4$)
Hardkernal is known for ODROID Linux Single board computers but this time they have come up with a very different product, a power supply with inbuilt power measurement.
This power supply can be used during product development and can help you monitor the power consumption and hence help you in optimization.
Current measurement is in milliampere range so it cannot used used for battery powered device optimization.
This supply was mainly designed for developers who are using Linux boards which generally consumes current from a few milliamps to a 1 – 2 Amps.
SmartPower 3 Features
LCD 480×320 3.5“ TFT LCD
- Two output channels (Max 50W + 50W)
- Output Voltage DC 3.0 V ~ adapter voltage -1 V
- Output Current DC 3A (Max) per channel
- Measurement Voltage, Current, Watt : sampling rate : 200Hz Max. (5msec interval)
- Tolerant 3% typical (above 5V 1A)
- LED RED(Power), BLUE(Alive) C, D
- Keys for ON/FF, channel Selection
- Encoder Switch for easy configuration
- Output Terminal 4mm diameter banana jack
- Input Voltage DC 9V ~ 21V using external adapter
You can connect the device via USB-C port and can monitor the power readings at 200 times per sec Max. (5ms ~ 1s sampling time) Max.
There is no software provided by the company, you can store the log in CSV format using readily available serial terminal and then open the file and plot on xls sheet to do the analysis.
Limitations
The price is attractive but make sure you understand the technical limitation before proceeding for a purchase.
- Current resolution is in milliamps
- PC software is not available for easy analysis
- Power supply can output min 3V, cannot go lower than that.
- External adapter is required.
From my point of view, if they add readily available easy to use software only then it becomes a useful power analysis tool, it is not that useful.
I hope found this article useful.
You can read my other interesting blogs & articles on embedded system design here.
I help embedded engineers and start ups build reliable and successful embedded products. If you need any help please let me know here.
Happy Learning to you!