If you have ever used your flash drive or external hard drive in someone else's computer, you may have been concerned about the USB port and whether it was wired correctly. Some years ago, a friend blew up a new flash drive by plugging it into an incorrectly wired USB port. Following that incident, he always tested USB ports with a USB light. I also got into this habit and I took a standard USB light and shortened the shaft to make the whole light around 90mm long. I keep this with my flash drive for testing unknown USB ports.
This project demonstrates how to convert a dead flash drive into a handy USB Port Tester that you can take with you and test unknown USB ports, before plugging in your valuable hardware.
Multimeters have been been around for decades now and most people use a digital multimeter these days, with the older style analogue instruments now being few and far between.
You might get readings such as 5.02V on your digital display, but just how accurate is your multimeter? Multimeters can be sent for re-calibration, but the cost of this service is usually more than the value of a low-end instrument. Now you can check the accuracy of a multimeter on the DC voltage ranges, with this low cost and easy to build precision voltage reference.