A while back I wanted to monitor how much current my iPhone could draw under different conditions. I had seen a cable before where somebody brought it into a project box with a couple of screws on top exposing the two unshorted positive leads and the straight-through ground (such that you could measure both current through the cable or voltage across it), but I felt I could make things both smaller and more fully-featured. My version uses an 8-up dip switch bank, two rows of four male headers, and a little piece of protoboard. Switches 3-6 can be turned on or off to connect or disconnect each of negative, tx, rx, or positive (useful for enabling the cable for data while you meter it). Switches 1 and 8 are unused, and switches 2 and 7 each connect one half of the RF shielding to the other (best avoid as much interference as possible – I just leave these on always).
I’ve found it super useful for characterizing various USB loads. One key aspect to the design is that I chose to use headers. This makes it easy to use my meter’s hook leads to measure power, or perhaps in the future, it’d make for an easy test hook connection for a logic analyzer. I built the inital version a while ago, but I didn’t have any real headers so I used pieces of solid-core wire. That was annoying and fragile, so today I added actual headers. Now it’s much cleaner and more compact.
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