I recently purchased a cheap usb current meter off ebay for a couple dollars from china to measure the quality of all my phone chargers I had sitting around my house. After I got it, I noticed it had a 3 to 30 voltage range so I thought of a way I could repurpose it.
I have a small homemade power supply I made a while back that I've been using that has to current or voltage indicator. I've just been using a multi-meter which meant I was always having to break the circuit if I wanted to measure the current. Not to mention I'd have to change the settings on the multi-meter and the way the probes are connected.
What I ended up doing was I made a small female usb breakout board(shown above) to connect to the input of the current meter. I then made a usb cable with flying leads for the V+ and ground to connect to power the circuit I am working on. I did a test using a 100 ohm resistor, and you can see below it reads 100 mA when I have 10 volts across it. The neat thing is this meter even calculates the resistance and displays that as well. I found however though , for any current readings below 100mA it is less accurate. It can be off as much as 10 or 20 mA. For its intended use though I think its ok.
The other thing I noticed was this meter also measures the D+ and D- voltage lines. I ended up hooking up a potentiometer to send 1VDC to the D+ line. Unfortunately the meter can only measure up to 3 volts on these lines. This could be useful for times where I want to monitor a low voltage, like a comparator reference or something.
Maybe in the future I will buy anther one of these and completely rebuild the enclosure for my power supply so I could monitor both the positive and negative voltage of my supply.