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Physical Hinge

A project log for InterBand

An open physical and electrical interconnect standard for wearable band modules

noviriumnovirium 08/17/2015 at 14:090 Comments

The point of the physical part of the InterBand standard is to only define the shape of the end of modules, allowing them to happily interconnect with a range of modules without unnecessarily restricting the shape or form of the rest of the module. For instance, battery modules would probably lend themselves to a flatter, thinner form intended to sit underneath the wrist, possibly with a lug on the side to house a USB micro port for charging. Smaller sensor modules would happily sit on the side of the wrist, being shorter and allowing a greater curvature.

There are several forms this hinge could take, and like the electrical connection, I'm yet to firmly settle on one. In general, it seems like a good idea to use two hinge sections, one on each side, with a gap in the middle for the electrical connection. While I'd like the body of the modules to be 3D printable, the hinge axis itself is something that should probably be a separate component. The goal is to have the hinge be similar in size to conventional watch bracelet links, 22mm wide and no more than 4mm high. At these sizes, a pin in a 3D printed hole would not be strong enough.

So far I've found two options for the hinge axis: either use standard watch band pins, protruding all the way through the hinge, or small screws (likely M1.6). It's reasonably easy to get hold of either of these. Watchband pins have the advantage that they're fairly low profile, but I suspect that they rely on fitting tightly into a hard wearing hole to retain their position effectively (not how I'd describe the ABS and PLA used in 3D printing). Another disadvantage of these pins is that they obstruct the middle of the hinge, meaning any electrical connection would have to go around the center axis of the hinge, rather than being able to pass through it as it moves.

Small screws would have to be used in pairs, one on each end of the hinge, and can self tap relatively easy into 3D printed plastic. A potential problem with them is that the thread might slowly wear on the sliding half of the hinge (possibly even loosening the screw)

Of course, having a triplet of interleaving lugs on each side of the hinge isn't the only option. I've briefly thought having a short bar snap into a sort of cup (think a closed lug with a slot cut into the side of it), but am pretty sure that trying to print this at diameters under 4mm would fail.

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