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Anelok: Mk 3 (20170314) errata

Werner Almesberger werner at almesberger.net
Thu Apr 20 18:24:35 UTC 2017


Of course, not everything went quite as planned. I found a
number of issues, fortunately most of them small:

https://gitlab.com/anelok/anelok/blob/master/hw2/ERRATA

I'm not done yet with design testing, so this list may still
grow. There are also a number of configuration choices and
deviations from the schematics:

https://gitlab.com/anelok/anelok/blob/master/hw2/BOARDS

Most of the deviations were caused by me not having the right
part - usually some resistor - at hand, and should have
negligible effect on the overall performance of the prototypes.
I omitted the power consumption optimizations (configuration
choices) for now. It'll be easy to test them later.

So far, so good. However, ...


I found a rather major blunder: I placed the footprint for the
OLED connector 1.9 mm too far to the right, and didn't notice
until I had the two prototype boards already made. One can see
it in this picture:

http://downloads.qi-hardware.com/people/werner/anelok/tmp/mk3-running/shift-oled.jpg

The OLED sits on the top of the case instead of going into its
cavity, and while the FPC (flexible printed circuit) connecting
the OLED flexes nicely in the Y and Z direction, it will not
budge in the X direction.

Moving the OLED opening in the case would eliminate the "bridge"
between OLED and buttons, and the buttons would then be free to
fall out - something they already enjoy way too much with things
as they are.


I solved this by shifting the whole PCB, right into the left
side wall. The tweaked case is on the left, a normal one on
the right:

http://downloads.qi-hardware.com/people/werner/anelok/tmp/mk3-running/shift-pcb.jpg

Fortunately, the wall is 2 mm thick, so the PCB only looks odd
there but doesn't stick out. Shifting the PCB caused the LED to
end up left off the center of the buttons.

The shift also means that the USB connector is too far from the
right wall. To still be able to connect to the board while in
the case, I grew the USB hole to accommodate also the overmold
of the plug.

A "normal" case is on the top, the tweaked one at the bottom:

http://downloads.qi-hardware.com/people/werner/anelok/tmp/mk3-running/shift-usb.jpg

I also had to trim the cylinders that hold the screws, and one
of them gets too close to the inductor, transferring mechanical
stress. You may have noticed the likely consequence in

http://downloads.qi-hardware.com/people/werner/anelok/tmp/mk3-running/teardown-bottom2.jpg

Fortunately, the inductor also works without that corner. Last
but not least, I moved the "nipples" at the bottom of the button
caps such that they still touch the centers of the tactile
switches.


The proper solution will be to correct the placement of the OLED
connector in the layout for the next board revision.

- Werner



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