A compact, electrically isolated, USB-controlled instrument designed to deliver accurate, stable constant current across more than seven decades of range, from 10 nA to 400 mA.

Unlike typical lab power supplies, this device is optimized for ultra-low-power and mixed-signal work, where nanoamp-level accuracy, repeatability, and electrical isolation are critical. It was originally developed as a calibration and reference tool for high-resolution power measurement systems, and has evolved into a versatile standalone current source for embedded development and research. It is NOT an SMU. You do not select a voltage output and then a current maximum. Instead you command a current from 10nA to 400mA, and this device provides that up to a voltage of about 4V.

The unit is galvanically isolated from the USB host, eliminating ground loops and protecting sensitive devices under test. Current setpoints are digitally controlled using an open-source Python interface, making it ideal for scripting, automation, and repeatable test profiles.

This fills a gap between hobby-grade current sources and professional SMUs, offering capabilities that are typically unavailable at this size and price point.

Key Features

• Constant current output from 10 nA to 400 mA
• Extremely wide dynamic range without manual range switching
• USB-powered with full galvanic isolation from host PC
• Digitally controlled current setpoint for automation and repeatability
• Designed for low noise and high stability at nanoamp levels
• Suitable for continuous operation across the full current range
• Open source hardware and firmware
• Compact form factor suitable for bench or fixture use

Typical Use Cases

• Photodiode or energy-harvester emulation
• Sensor and analog front-end characterization
• Testing 4-20mA sensor interfaces
• Calibration of power measurement tools and shunt systems
• Research, education, and lab automation
• Testing of LEDs for brightness evaluation or other constant-current devices

Specifications

• Output mode: Constant current source
• Current range: 10 nA to 400 mA
• Power input: USB
• Electrical isolation: Yes (USB to output)
• Control interface: USB (software-controlled, open source Python interface)
• Hardware / firmware / software: Open source

Accuracy

I performed detailed analysis of the accuracy of this device, which can be found here. The high-level summary across current scales is shown below.

I also performed physical accuracy testing using a 6.5 digit desktop digital multimeter here, which showed perfect accuracy within the measurement accuracy of the multimeter every time, from 20nA to 389mA.