When you’re working with USB devices you often need to measure the overall power consumed. You need to measure Current (Amps) and Voltage (volts).

Sometimes you’re trying to add power management support to a driver, perhaps the device feels hot even when its not being used. If this bothers you enough to investigate then you’ll probably end up modifying the device driver to control the power dynamically. Neat! You’ll need to validate your work by measuring power before and after any changes you make.

Another use case: Perhaps you’re not dealing with a heat issue, but perhaps the device is unstable in certain modes of operation. For example, Analog TV mode vs Digital TV mode. You might want to look at power consumption to understand the differences.

The USB2.0 specification generally states that USB2.0 compatible devices should draw no more than 500ma of current. Perhaps your unstable or warm device is going over the recommended power budget? (Sidenote: Most PC Motherboards will happily provide more than 500ma of current).

You can measure power a number of ways but if you want something relatively cheap and mostly accurate, for the price of a couple of large coffees, I have something to recommend, the AboveTek USB Current/Power Meter.

Checkout the Amazon pictures to see exactly how you connect it. You’ll see it goes in-line inbetween the USB cable from your device to your computer. The LCD display toggles between Volts and Amps and has precision to two decimal places.

For fun, I measured the current and voltage of a device independatly to see how reliable the AboveTek measurements were. The good news is that the Voltage measurement is accurate all the way down to 10mv. Slight downside, the Current reports lower than ideal values by approximately 20ma.

To put this into perspective, a USB device may draw 460ma of current from your PC USB port, the AboveTek word report it’s drawing more like 480ma. Not a big difference but an annoyance.

Should you buy one of these when you already have a perfectly good Multi-Meter? Probably yes. It takes five seconds to plug the device in and start taking measurements. By contrast, it probably takes you a minute or so to grab the meter, connect the probes, find your magic inline usb power cable or special power break-out do-hickey widget.

When I’m working on non-company projects at 3am, it now only takes a moment to take a quick USB power measurement.

Based on measured usage, the AboveTek device consumes 20ma of current and automatically attempts to compensate for its own power burden in the resulting LCD information.