Re: Advice in mini-ITX

On Sat, 17 May 2008 23:53:14 +0100, Martin Gregorie wrote:

[SNIP]

The trigger for this interest was being given a pair of Fujitsu 20 GB
2.5"
drives that came out of Pace HDD VCRs. Are these likely to be always on?
Is there any way I can easily find out?


Check the model number against the manufactures data***. Like I said
very few are, and will die after about a year being on 24x7. You can get
around two if you get them sleeping through the night. It is just not
worth the hassle.


For power I use a picoPSU at 60W. The idea here is that with a 6-26V DC
input I can build a battery backed PSU rather than a UPS. The concept is
that the a 12V lead acid can provide the power when the mains goes away,
without conversion back to mains. That said I have not got around to
actually building it yet. The only issue is this version does not
produce much on the 12V line so all storage has to be laptop based.

Good idea. I like the idea of having the battery continuously on,
especially as it should make a decent buffer against mains
fluctuations and spikes. You'd really need a dual mode charger (one with
bulk charge and trickle modes) if it is to do much more than keep up with
the computer's demand. Otherwise it will just wreck the battery, but I
expect you know this already. Does anybody know if the Maplins dual mode
chargers can switch back to bulk charge from trickle mode without being
switched off and on again? They're good chargers though not terribly
efficient judging by their normal operating temperature.


The problem with the trickle chargers is that they don't provide enough
juice to power the system and trickle charge. After some more thought and
some Googling at the weekend, I am thinking of one of these

http://www.powerstream.com/DC-UPS-1212-5A.htm

Would be just the ticket, and designed for the job. What I would like to
do though is add some sort of battery level detection so I can
automatically shutdown the machine before the battery protection kicks in.
The question is whether to use a simple comparator, battery protection
kicks in at 10V, comparator signals on the serial port at say 10.1V by
twiddling a status line. Or do I do a ADC level detection between 13.1 and
10V for battery capacity, something like a TLC548 with an op-amp level
shifter in front and bit bash the serial port. A bit more complicated but
much more pro :-)

I would also want to assert the ring indicator on mains power, so I can
have "Wake on Ring" set in the BIOS to automatically bring it back when
the mains returns.

Power would come from a toroidal mains transformer, but with centre tapped
rectification, avoiding the second diode voltage drop with bridge
rectification, and using some nice expensive Super Barrier Diodes for
extra efficiency. One does not need a regulated output cause the DC-UPS
and the picoPSU take care of that at silly >95% efficiencies anyway.


I used a Pack-Box A4 for the case, with the fan removed (my system is
fanless for increased reliability).

I like the look of the Morex Venus 669 case:
http://www.mini-itx.com/store/?c=3#venus
because I don't need the rig to be all that small and I like the
tidiness of an internal PSU.

Well the picoPSU is internal :-) The idea is for the battery backed PSU to
be in a separate wall mounted box, mounted next to the server. It is all
under the stairs, and pretty tidy anyway.

If I was being really pro I would build it all into a 10" rack cabinet

http://www.cablemonkey.co.uk/acatalog/cabinet.html


Finally I have my own design radio clocks (both
MSF and DCF77) hooked up to a serial port. The whole lot is mounted on
the wall under the stairs.

I forgot to mention serial ports. Thanks for the reminder: I need two of
those too. One for an MSF clock (your design!) and one for transferring
data (devices like a Garmin GPS II+ and an EW flight recorder).


The Via board that I use has one on the ATX IO plate and a header on the
board for another.


JAB.

--
Jonathan A. Buzzard Email: jonathan (at) buzzard.me.uk
St. Andrews, United Kingdom.
.