The idea for this project came about when I was experimenting with some homebrewed circuitry that, as so often happens, was powered from the 5-V supply from the USB port of my computer. What followed was an error message from the operating system saying ‘USB Hub Power Exceeded’. Unfortunately, all communication with the circuit under test also ran via this USB port, making troubleshooting somewhat difficult. What I needed was a tool that could indicate how the power supply was holding up with the connected load — and not shut down immediately if the limits were exceeded. The computer should also remain protected, to avoid any loss of USB communication, even when using an external power supply. Here is my solution.