If you need to log voltage over time, this does the trick. The Voltmeter with USB interface designed by Tindie Seller Digital Measure is a small module that measures voltage on a set of screw terminals and sends the data to a PC via the USB connection.
Measurements are made with an ADC using an optical isolator, so you don’t need to worry about transient voltage making it back to your USB port. There is also a voltage divider and an EMI filter at the input of the A/D converter.
All of this convenience extends to the software side of things as well. The PC software is a simple windows application that will display the value and even lets you save the data in a CSV file format. The API is based on the .NET framework if you choose to roll your own software.
Finally, the USB works as a Human Interface Device (HID), utilizing drivers already present in Windows. So once you plug in the USB, it is immediately ready for use!