Right now, the battery is held in place by the following contraption: http://downloads.qi-hardware.com/people/werner/anelok/tmp/case-bot-clip.jpg
The idea is that the case bottom presses against the clip which in turn presses against the battery which thus makes contact on both sides. This work, but not very well. In particular, since the two case halves do not have a lot of vertical pressure, contact is easily lost when handling the current Anelok prototype. Joining the two case halves with screws may improve this. A production version could perhaps also use a custom-made steel clip that doesn't depend so much on external pressure. But to play it safe, I'm thinking of using an industrially made battery holder in the next prototype. Advantages: - holds the battery firmly, - does not depend on the case for support, and - can be globally sourced. Disadvantages: - larger than my current contraption, - thicker, too, - cost (see below), - sourcing risk (hopefully minor). Now, there are many designs to choose from ... http://downloads.qi-hardware.com/people/werner/anelok/tmp/bat-holders.jpg The simplest type I know is a single metal clip that presses the battery onto the PCB, a concept not too dissimilar from what I have at the moment: http://www.digikey.com/product-detail/en/BK-913/BK-913-ND/2329371 It's also pleasantly inexpensive (USD 0.22 @ 1000). It has three big drawbacks, though: - it exerts an enormous pressure on the PCB which also makes it hard to remove the battery, - the battery is accessed on the side so there has to be a free path in that direction which also limits the possible orientation, and - it's through-hole so there have to be sufficiently sturdy mounting holes. There is also an SMT version of it but that one doesn't even stay on the PCB if not bolted down in addition to soldering. There are various types with a round plastic shell and a "crane" type of clip but they're all quite tall. The ones at 5 and 6 o'clock in my collection are quite nice when it comes to battery removal (you press down on the little plastic tongue to release the battery) but are also rather bulky. Now, the one in the rear at 1 o'clock is also a full holder but more slender. One of its drawback is that it holds on to the battery with surprising strength - while you can pry it loose just with your fingers, a screwdriver will make this a lot easier. There are now even smaller variants of the same concept (at about USD 0.60 @ 1000): http://www.digikey.com/product-detail/en/LP2032SM-JJ-GTR/LP2032SM-JJ-GCT-ND/4246309 http://www.digikey.com/product-detail/en/BLP2032SM-GTR/BLP2032SM-GTR-ND/2077832 Using one of these would make Anelok thicker by about 1.0-1.2 mm. With a little luck a small cavity could be made in the bottom plate to accommodate the center pin of the wheel, which would allow moving most of the battery holder under the wheel. As an added benefit, traces could be run under the holder since. - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
