Archive for June 5th, 2010

Bike Helmet Earbud/Mic Connections

I’m in the process of reworking the interface box between the amateur radio HTs on our bikes and our helmet-mounted earbud & mic lashup. Mary needed a new helmet before I got the new interface ready, soooo there’s an adapter cable in the middle.

This time around, the helmet cable uses a male USB-A connector, rather than a female 6-pin Mini-DIN PS/2 keyboard connector. Either one is cheap & readily available as assembled cables, which gets me out of soldering teeny little connector pins. These days, though, USB cables are more common.

The motivation for a non-latching, low-extraction-force connector at the helmet is that when (not if) you drop the bike, the helmet doesn’t tie your head to the bike and snap your spine. Falls on a recumbent are much less exciting than on an upright bike, but you still want the bike to go that-a-way while you go this-a-way. Been there, done that.

The old helmet cable connector: female 6-pin mini-DIN. The wire color code is not standardized. Viewed from rear of female connector or the front of the male connector, with the key slot up:

 ear com - Gn   5  |_|  6  K - ear hot
 mic com - Or   3  key  4  Y - mic hot
        gnd - Bn  1   2  R - gnd

The new helmet cable connector: male USB-A. Mercifully, they standardized the wire colors. Looking at the front of the male USB-A connector with the tab down and the contacts up, the pins are 4 3 2 1:

  • 1 – R – ear hot
  • 2 – W – mic hot
  • 3 – G – mic com
  • 4 – K – ear com

The female USB-A connector is exactly the same.

That arrangement should produce the proper twisted pairs in a USB 2.0 cable, but all the USB cables I’ve seen so far lay all four wires in a common twist inside the shield. Maybe it’s the cheap junk I buy, huh?

It’s worthwhile to scribble some color in the background of the trident USB symbol so it’s easier to mate the connectors.

Easy-align USB connectors

Easy-align USB connectors

Memo to Self: verify the connections & proper operation before shrinking the tubing!

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