Jake Wachlin's MetaShunt Is a 10,000,000:1-Range Current Measurement Device for Low-Power Projects
Offering a range from as low as 50nA to 500mA, the MetaShunt delivers power analysis for even the lowest-power of devices.
Maker Jake Wachlin has designed a device that aims to accurately analyze the power usage of ultra-low-power gadgets, including those built for use on the Internet of Things: the MetaShunt, a "high dynamic range" current measurement tool.
"MetaShunt leverages a simple idea," Wachlin explains of his design. "By quickly and accurately measuring the voltage across a current shunt resistor and engaging additional shunt stages when needed, MetaShunt ensures that it can provide accurate current measurement across a range of approximately 10,000,000:1 (from 50nA to 500mA) without providing [a] significant voltage burden."
That range, from nanoamps to milliamps, wasn't chosen at random: MetaShunt was designed specifically for ultra-low-power devices, in particular energy-sipping projects built for the Internet of Things — and delivering the accuracy required to test not only the hardware but the software too.
"By measuring current rapidly over time," Wachlin explains, "the total energy use during a given portion of your code can be determined. MetaShunt acts as a virtual ground for your system, so that you can use your battery. Or, MetaShunt can provide 3.3V or 5V to the system under test if desired."
When connected to the device on test, MetaShunt streams measurement data over its USB port at almost four kilo-samples per second (4kS/s), Wachlin says — with a "burst mode" offering 25kS/s using on-board buffering. Open source Python-based software provides an easy way to capture the data including setting burst-mode to trigger on current rising above or falling below a set current threshold.
The MetaShunt is listed on Wachlin's Tindie store at $249, though at the time of writing was showing as out of stock; the software sources are available on GitHub under the permissive MIT license.