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On Wed, May 30, 2007 at 10:13:10AM -0400, Timothy J. Weber wrote:
> Peter Todd wrote:
> > Unfortunately in this case the device is going to be battery powered,
> > so heaters are totally out, well, almost, plutonium powered heaters
> > would last long enough... :)
> 
> What's your budget?  :)

I've heard the last time Nasa needed some plutonium for electrical
generation on one of their probes even they couldn't get enough due to a
slowdown in work at Sandia Labs due to a security incident.

That said, I hear depleted uranium is something they're trying to give
away, not that I've ever found a nice online store to buy a kilo of it.
Love some to go on my keychain next to my tritium glow stick, sutably
encapsulated of course, it is a chemically toxic heavy metal after all.

> > A conformal coating wouldn't work in my case as I have a display, and I
> > don't want condensation between the display and the (acrylic) walls of
> > the box. 
> 
> Seems like you have two potentially separable issues, then - 
> condensation causing electrical shorts on the board, and condensation 
> getting in the way of the display.

I should clarify, not so much shorts per say, but rather condensation
draining the limited lithium batteries.

> Can you bond the display flush to the box wall with some clear adhesive? 
>   Or cast the display face in resin to make a piece that could bond 
> flush with the display wall?  Then you could conformal coat the rest of it.

It's an interesting idea... but it could add a lot of complexity. One of
the more "interesting" things about the displays I'm using, the
ChLCD "electronic paper" displays from Kent Displays, is that they are
very pressure sensitive. If you touch them at all they leave a ugly
visible mark that won't go away until you do an electronic clear.

So in the case of the fully encapsulated option the thickness of resin
was going to be fairly thick, at least half an inch, maybe more, to
resist flexing. Any mechanical pressure on the encapsulation would be
immediately transmitted to the display surface.

If there is an airspace between the display face and the enclosure
things get much easier.

Not to say it isn't doable, but it's a lot more work, and then I have to
worry about stuff like bonding the polyester resin to the acrylic making
up the rest of the enclosure.

- -- 
http://petertodd.ca
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