An SMU or Source Measurement Unit works a bit like a power supply, in that it can source current into a load and a bit like an electronic load, in that it can sink current from a power source. It includes a crossover circuit, so that it cleanly and predictably swaps between sink and source modes automatically. This makes it terribly useful for testing all manner of power circuits, charging and characterizing batteries or just saving bench space by replacing two separate boxes.

This DIY-SMU from analog electronics guru [Dave Erikson] is a full four-quadrant design, meaning that it can operate with both positive and negative voltages. The design shows excellent performance, comparable to commercial instruments that cost serious money, which is testament to [Dave]’s skill and experience.

The quadrants can be understood if you imagine a graph with voltage on the horizontal axis, and current on the vertical. Both axes can swing to both polarities, with quadrants I & III indicating power delivered into a load and quadrants II & IV power absorbed from a source.

The very detailed project logs show every gory detail, every problem found and the work to solve it. Its a long read, which for those interested in such devices, will be time well spent in this scribe’s humble opinion.

The DIY-SMU is mostly analog in nature, with the control portion courtesy of a Teensy 3.2, with a Nextion TFT display with touch for the user interface. The firmware even supports SCPI over USB to allow remote control and data gathering, so its ready to drop right into your test and measurement stack. For more reading goodness, checkout JSMU, a related project, taking inspiration from the DIY-SMU. Details can be found on this project GitHub repo.

Many power supply projects have graced these pages over the years, like this 2015 Hackaday Prize Entry but this is one of the few four-quadrant designs to be found, so hats off!

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