Anelok: case design (3/3): omissions and known bugs
werner at almesberger.net
Fri Jul 10 22:23:35 UTC 2015
There are a few known issues in this design:
- the barrels in the bottom half only attach to the battery bay
but not to the bottom face. This is not completely wrong (i.e.,
with stiff enough plastic and a good 3D printer, this ought to
work), but might be inconvenient to manufacture.
- the "funnel" of the USB receptacle is about 1.6 mm from the
outside wall, but the standard only gives us 1.3 mm to work
According to the Micro USB 1.01 specification, the main body
of the receptacle should protrude 0.7 mm over the PCB edge,
plus 0.3 mm for the "funnel" (both in figure 4-11 on page 24).
Then there is a clearance of at least 1.3 mm between funnel
and the overmold of the plug (figure 4.9, page 22).
That's a total allowance of 2.3 mm between PCB edge and outside
wall, while we have 2.2 mm. So making this fit nominally may
just be a question of moving the USB receptacle closer to the
PCB's edge. In real life, we'd want a bit more mechanical
tolerance, too, I'd say at least 0.4 mm.
- there are no cut-outs for USB and the switch yet.
- for the switch, I should also design the user-visible knob that
I'm having second thoughts about horizontal placement of the screws.
Now that I know that relatively short threads are available, it may
be better to design with that in mind, and make the screws
perpendicular to the bottom face. Near the battery, we have about
7 mm between the outer surface of the bottom half and the bottom
side of the PCB. A 5.0 mm screw (thread length) should therefore
A vertical arrangement would allow moving the screws closer to the
battery, since the bulky thickening around the head would slide
under the curvature of the battery cover. The screws could also be
offset by a few mm from the side, thus making room for components.
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