[onerng talk] The world's (other) most secure TRNG

[Paul Campbell]

On Sat, 11 Oct 2014 21:55:54 Bill Cox wrote:
> It's very low-speed, but I think secure.  I'm sure anyone with any
> experience could tell me the 100 things I got wrong on this tiny design.  I
> welcome such feedback.

so some minor suggestions:

- the circuit board etch USB pug  idea is cheap and cool - but it's is 
terribly unreliable (everyone with one of my programmers that use this rightly 
complains) - I've switched to proper plugs (SMT plus 2 thru holes) - for what 
you're doing you need to tape your board out in 2mm thick board (2.2-2.4 if 
you can) with ENIG plating, and even then you'll usually need a bit of masking 
tape on the back of the connector to stop it falling out of some sockets

- I prefer to lay down ground planes on both sides and have Eagle take care of 
them- in Eagle create a polygon on each side then name it 'gnd' the click the 
flow (ratsnest) button - personally for my RNG there are NO traces on the 
bottom under the analog portion, it's all shield - drop vias where possible to 
stitch the two planes, and drop vias next to ground pins on ICs

(your analog world may require more of an audio approach to grounding - you 
can create split ground planes pretty easily using this technique)

- you can likely get away with much much smaller vias (check the eagle layout 
file you got from your board house - I typically use .35mm) - ideally you want 
them small enough that they get tented with solder mask

- looks you probably don't have the layers on that handle component 
restriction layers - that's OK for something you're planning on assembling by 
hand - a P&P machine might run into trouble (just a guess from eyeballing it)

	Paul