Keychain microUSB cable

Why

Many devices, from ebook readers to cellphones, now use microUSB connectors. Often it is needed to connect them to a computer in an unexpected situation. As few people routinely carry cables, a rather frustrating situation often occurs when the only thing missing for a successful data transfer is a stupid cable.

A short cable was therefore devised, optimized for wearing on a keychain. The design criteria were mainly small size and robustness. A 5-cm short cable was therefore chosen, as a compromise between easy portability and sufficient length to attach most devices to most USB ports; the awkward mutual position of the device and a host computer is considered the cost of the always-on availability of the cable.

Construction

The cable is built from standard USB-A and microUSB-B connectors. Twisted pairs from a Cat5e stranded-wire cable were used on the basis of availability and thickness; the relatively thick multistrand wires suggest hopefully decent degree of mechanical robustness and resistance to breaking.

For compactness of the assembly and protection of the fragile microUSB connector, a microUSB female was soldered to the top of the USB-A connector. This allows snapping the cable ends together, forming a fairly compact loop.

The wires were soldered to the connectors and secured with hot glue. A bare stranded wire was added to connect the shells of the connectors; this wire was purposely made a little shorter to carry most of the mechanical loads, as in addition to being somewhat disposable it is also thickest of them. The wire bundle was coated with a transparent heat-shrink tube for added mechanical protection. The ends were protected with few layers of a heat-shrink tube to increase the diameter to better fit to a larger heat-shrink.

Larger heat-shrink tubes were used as connector housings for both the A and micro-B sides, due to the much smaller achievable form factor than if regular plastic housings were used. The few millimeters saved are pretty significant for a keychain.

Drops of red and blue paint were used to mark positive and negative side of the connectors, for the purpose of eventual in-the-field improvisations.

For better aesthetical factor, the USB-A side was spray-painted matt black. Tissue paper was stuffed into the connectors, the cable and microB side were wrapped in sticky tape, and paint was applied. After drying, the tape was removed.

Images

Parts	MicroUSB female connector on the male	MicroUSB female connector on the male	MicroUSB female connector on the male
Internal assembly	Internal assembly	MicroUSB side	USB-A side
MicroUSB-F and eye	Heatshrink-insulated	Heatshrink-insulated	Heatshrink-insulated
Heatshrink-insulated	Heatshrink-insulated	Heatshrink-insulated	Heatshrink-insulated
Snapped together in a loop	Snapped together in a loop	Snapped together in a loop	Painting
Painting	Black-painted	Black-painted	Black-painted
Black-painted