[Cryptech Core] Alpha rev.03

[Pavel Shatov]

Hello!

Now that critical subsystems in Alpha rev.02 have been tested, it's time 
to order a larger batch of boards for Berlin. Before that Fredrik and I 
are going to do several changes and increment board revision number.

The most important change is form factor. The board was initially 
designed to be compatible with Intel NUC (101.6 x 101.6 mm) platform. 
That seemed like a cool choice at first, but turned out to be a 
disappointing mistake later. Apparently Intel produced several 
generations of that platform and they have minor mechanical differences, 
but this isn't clearly documented anywhere. Another sad thing we 
discovered is that despite Intel offers a huge NUC ecosystem catalog 
with literally dozens of third-party cases, it's too difficult to buy 
them if you need say 25 or 50 pieces.

Our idea was to switch to a Eurocard form factor (100 x 120 mm, aka 
"3Ux120"). That would require minimal board changes and gives us a much 
broader choice of cases.

Speaking of changes in schematics, we only edited the part related to 
USB interfaces. Right now we have Tx & Rx LEDs connected to FTDI 
transceivers, that should blink when there's activity on UARTs. We 
overlooked the fine print in the datasheet saying, that those LEDs will 
only work when there's an external configuration EEPROM available. We 
are not going to have that EEPROM, so we removed the LEDs, because they 
would be dead anyway. We also have 6-pin headers, that allow people to 
design custom USB-UART transceivers instead of using on-board FTDI 
chips. In rev.02 we forgot to expose +5.0V (Vbus) from USB connectors 
through those headers, this will be fixed in rev.03 (Peter, hello :)

I think, the only unresolved issue is backup battery. When the 
corresponding jumper is not inserted, there's still ~2.5V on Vbatt, 
which must be leakage from the 3.3V rail. I'm afraid, we don't have 
enough time right now to debug this, because production cycle is around 
5 weeks and to be on time for Berlin we need to order boards no later 
than on the forthcoming Monday.

There are no other essential changes besides relocation of some 
connectors to accommodate the new form factor. Latest PCB project can be 
download from https://yadi.sk/d/Ka-sOEf9s2K3w
Note, that you'll need to install free Altium viewer to open it. The 
project itself is still called "rev.02", because we were too afraid to 
remove all the files from it, rename them, then add all the files back 
and re-compile. The archive contains a file named "rev.03.txt" with 
details of what exactly was modified and "rev.03.pdf" with the latest 
schematics.


-- 
With best regards,
Pavel Shatov