Paul Dugas wrote:
> Anybody know of something like a Soekris net4801 board/chassis with a
> temp spec of -40 to +85C? One that can run m0n0 obviously ;)
Conditioned enclosures are available that will keep an otherwise solid
PC-like board in
environmental conditions that it can survive.
Getting the actual board to survive in those extreme temps will be quite
difficult. At the low end you'll have to deal with both condensation
(freezing condensation) which can create shorts on the uninsulated
traces (on the PCB) as well as the pins and solder joints for the
components places thereon.
You'll also want to think about the very real possibility of a "cold
start". That is, if the power fails, and the entire board gets to
sub-zero temps (esp -40C (which is the same as -40F,)) then the crystal
oscillators(s) on the board can freeze. Without the crystals, you get
no clocks. Without the clocks, you get nothing from the CPU and other
components that require at least one stable clock.
This is why many conditioned enclosures have heating elements that
maintain the inside of the enclosure to a temperature just above freezing.
At the high(er) temps, you'll have difficulty with the decreasing "theta
T" or difference between the case (and junction) temperature of the
components on the board and the temperature inside the enclosure, as
well as the decreasing theta T between the temperature inside the
enclosure and that of the ambient outside of it.
Note that 85C = 185F, and such an atmospheric ambient has never
naturally occurred on the earth (though ground temps of 185F have been
measured quite close to volcanic sites. (In fact, the highest
atmospheric ambient ever recorded on the earth is some 50F less.)
Thats not to say that a poorly-designed or poorly installed enclosure
can't submit the electronics inside it to extreme (even fatal)
temperatures, but keeping the enclosure from being an oven is often
1) paint (or powder coat) it a light color. There is far less heat
gain from solar heating for a box painted a light color than one that is
painted a dark color.
2) shield it (my favorite trick). keep the direct solar loading
(heat gain inside the box) at a minimum by keeping the box shaded as
much as possible, while allowing circulation around the box.
3) keep the box as small as possible, though properly shaded, larger
boxes have more surface area to shed the heat being generated inside the
box. (That same surface area bites you if its
being heated by the sun.)
4) keep the heat being generated inside the enclosure to a minimum.
You're on the right path
with a Geode (or perhaps VIA) CPU.
Be careful, you'll find many companies who claim "-40 - 85C" who can't
really do it. Test it yourself before you accept more than a small
quantity of any offered solution.