Anelok: towards Mk 3 - new PCBs (1/3)

[Werner Almesberger]

A while ago I finished the schematics for Mk 3, and recently also
the layout. Since the goal is to make Anelok as small as possible,
the PCB size depends the on shape of the case, which is why the case
design had to stabilize before I could proceed with the layout.

The schematics:
http://downloads.qi-hardware.com/people/werner/anelok/tmp/mk3-partial/anelok.pdf

The design files for the circuit live in
https://gitlab.com/anelok/anelok/tree/master/hw2

There are a few changes I haven't mentioned on the list yet:

- I've removed the mechanical rfkill switch and replaced it with
  an electronic one, controlled by the cMCU. The reason is mainly
  that I couldn't find a good place for this switch to go, and that
  it would have made assembly of the device quite messy.

  I'll eventually want to move control of the switch to the sMCU,
  which is more trusted than the cMCU.

- I've added an optional low-voltage mode to reduce standby current.
  It works by letting the sMCU choose whether the boost converter
  delivers 3.3 V or 1.8 V.

  All the MCUs - including BT LE - can operate at 1.8 V, and having
  to boost the battery voltage to only 1.8 V should save some power.

- In addition to the sMCU LED, also the cMCU LED goes under the
  buttons. The idea is to make the buttons diffusely translucent, so
  one can see the LEDs through them.

I've started to assemble two boards. In this picture, the upper PCB
shows the top side and the lower PCB the bottom side:

http://downloads.qi-hardware.com/people/werner/anelok/tmp/mk3-partial/pcbs-partial.jpg

On top there are the cMCU and the sMCU, and the tactile switches.
The display and the cMCU's crystal are still missing. On the bottom
we have the USB connector, the memory card header, and the boost
regulator. The RF section is still missing.

>From a different angle:

http://downloads.qi-hardware.com/people/werner/anelok/tmp/mk3-partial/pcbs-partial-angled.jpg

- Werner