[time-nuts] looking for low-power system for gps ntp timekeeping

[Hal Murray]

folkert at vanheusden.com said:
> I own a couple of GPS modules (garmin 18(x) lvc) which I would like to use
> as a time-source. Now my server already has such a module connected (via
> gpsd and a pci rs232 interface) and my raspberry pies too (adafruit modules)
> so I'm looking for a low-power computer with a complete RS232 connector
> (DB9) with all signals attached so that I can feed it a PPS. Also real RS232
> so that I don't have to mess with resistors and such.

I'm not sure what you mean by "resistors and such".  At a minimum, you will 
have to do some wiring to provide power.

> I'm considering either this one:
> http://www.antratek.com/nanosg20-with-128-mb-sdram-and-512-mb-flash
> or this one:
> http://www.antratek.com/ontwikkelboard-met-cirrus-logic-ep9302
> What do you guys think: would they be any good for
> timekeeping? Known issues?

Both web sites have schematics.

On the Olimex board, there is nothing connected to the PPS input pin.  It is 
a dev board, so it should be easy to connect up power and PPS.

On the Ledato board, there are level shifters on all the signal pins.  One of 
the connectors has a slot for a resistor to supply power on RI.

------------

I think there are 2 basic approaches.

One is to use a board like the above or others that have been discussed here. 
 You will probably have to do some fiddling.  They don't have a real disk so 
you may not want to do a lot of logging.  This is the lowest power approach.

The other is to use an embedded PC.  If you get one with an Atom chip, the 
power can be pretty low.  I have one (with disk) that uses 14 watts.

-------------

There are a handful of tangled considerations:

Cost of initial gear and cost of power:
  You can get refurbished PCs for under $200.  An embedded type PC with an 
Atom chip will pay for itself in under a year.

How much fiddling do you have to do to the hardware?
How much fiddling do you have to do to the software?
  Using a real PC often simplifies both.
  If you can find a HOWTO type web page, that may be good enough.

PCs use display and keyboard/mouse to get off the ground.  Low end boards 
without a display probably default to using an RS-232 port to get off the 
ground.  Once you get setup, you can probably run both over the Ethernet.

Some PCI-RS232 cards have a jumper to supply power on one of the signal pins. 
 They were intended to power things like scanners before USB.  (I'll fish out 
some details if anybody wants them.)  You still have to solder the wires from 
the GPS hockey-puck to a DB-9 connector.



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