Embedded devices

Levi Pearson levipearson at gmail.com
Thu Dec 19 09:20:54 MST 2013


On Wed, Dec 18, 2013 at 2:07 PM, Matthew Frederico <mfrederico at gmail.com> wrote:
> This may be a question more for a hackerspace community .. but it is linux
> based.
>
> I am consulting for a small local Utah company who is entering the market
> with a platform of embedded hardware that essentially does edge
> *hardware*monitoring.  It's utilizing modern wireless (900mhz and up)
> and current 3G
> and 4G networks to "phone home" about how certain aspects of how hardware
> is performing - e.g. uptime of security cameras, switches, routers yadda
> yadda .. Its pretty ingenious  idea - but I digress.
>
> We're currently looking to perform some weatherproofing and was wondering
> if any embedded linux gurus out there had any tips regarding inexpensive
> heating/cooling?  Many of these devices will be "living" outside and some
> in extreme (arctic) weather conditions, especially devices that are
> security related.
>
> I have heard methods ranging from immersing entire PCB's into vegetable oil
> to creating a "heat" process that waits for low system load to increase cpu
> usage thus inducing heat...
>
> Anybody out there find any success with keeping hardware warm and cozy?

I am an embedded engineer, though the most demanding environment I've
had to work with is automotive. But the automotive electronics
environment is demanding enough and of high enough volume that there
are generally custom 'manufacturing grades' for automotive use, as
they have to function in harsh weather and EM environments as well as
conform to strict EM emissions restrictions.

Anyway, extreme temperatures are definitely an issue for electronics,
especially the analog portions of a board. Most analog components do
change their operating characteristics based on temperature; they're
typically imprecise to begin with. Good boards are designed to not be
terribly sensitive to component variation, but it's especially
important when extreme temperatures are in play.

Wide cycles in temperature cause unequal thermal expansion across the
different materials on a board. This can cause problems at solder
joints, especially if they're questionable to begin with. Any
mechanical components (spinning media, servos, etc) are going to be
especially sensitive to cold, and you'll want to be sure that you
specify ones that have been designed to operate in the temperature
range you will be seeing.

If you're using batteries at all, be aware that typical batteries
function poorly at very low temperatures. Be sure you look at the
temperature ranges of any batteries you specify; I believe lithium
battery chemistry is a good cold-weather choice.

So, with that out of the way, it seems the two general approaches you
can use are to build something for a harsh environment; one would be
to make sure the design functions correctly in the environment, and
the other would be to manage the operating environment.  Managing the
environment is not terribly difficult if you have a continuous power
supply and a big power budget, and certainly makes component selection
and design much easier.  Some insulation, a thermostat, and a heater
are pretty easy to design, but that's not very power-budget conscious.

Here's an article with some more discussion on cold weather design:
http://www.ecnmag.com/articles/2012/12/design-electronics-cold-environments

As for environmental management, there are solutions like this that
might already be in place for the equipment that's to be monitored:
http://www.oksolar.com/enclosures/heat_smarter.htm

Another option to manage the temperature of just your device would be
Peltier junction technology.  This company makes them and supplies a
lot of good information on their site: http://www.tellurex.com/

Hopefully at least some of that was helpful. Good luck with your
design and engineering!


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