But that design used a keyring recoil, which was quite strongly sprung. I wanted one that latched... like one of those USB cables for laptops... so I picked up a couple for cheap and started experimenting.
Step 1: Gather Your Materials and Tools
1) two retractable USB cables. Can be USB extension or power or anything. No electrical signals are transmitted. I got a set of 3 for �1 each in Pound Land.
2) a photo-frame style micro memory stick
3) A spare keyring
5) epoxy resin
6) stiff wire for twisting
7) electrical tape
1) couple pairs of pliers
2) wire cutter
3) measuring calipers
4) Sharp craft knife or set of knives
Step 2: Version II
Then on the remaining end, I clipped off the plug and tied the micro usb stick to the end.
Version II works but isn't very satisfactory.
Step 3: Interlude
The drum has a large coiled spring inside. The cable enters and goes around a channel at the side, which keeps it out of the way of the spring.
The other side of the drum has a complex pattern of channels cut in it, and there's a small ballbearing that runs in those channels to provide the latching effect.
Step 4: The Fun Bit Begins
The USB plug was not so cooperative. I had to destroy two of them to save the two parts I needed: the metal shielding and the plastic/rubber body. The innards I threw away because they are getting replaced by the micro USB drive.
The second picture shows the innards, and the flash drive inserted into the shielding for a test.
Step 5: Measure Twice, Cut Once!
The original innards were 1.7 mm thick, whereas the strpped-down flash drive was only 1.3 mm. So I needed 0.4 mm of padding. As it turned out, three thicknesses of electrical tape did the job. I stuck them on the back of the flashdrive and trimmed them carefully with scissors.
Also in this shot are the cable end and the body of the other plug, which I cut in half in order to hollow out to accommodate the flash drive.
Step 6: Assembly
To attach the cable, I got a small length of stiff wire and twisted it around the end of the cable, just to make an "anchor", and hollowed out a bit of the body to accommodate it.
Then mixed up some expoxy and set everything in position.