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On Sat, 3 Sep 2011, Ed W wrote:
On 31/08/2011 16:48, Bill Unruh wrote:
On Wed, 31 Aug 2011, Ed W wrote:
...
I'm building something completely different, but I have similar
requirements to try and get accurate time at boot for an unattended
router type device. I'm also considering including a BlueNext GPS that
appears to come in around the $16 mark (if someone knows of a cheaper
source for USB GPS units then interested to hear?)
With or without antenna? And how do you get the timing info out? (usb
is not
so good at interrupts)
There is no PPS on the bluenext thing, so you are constrained to NMEA
accuracy. As such it's definitely not hyper accurate, but it will get
you within single ms accuracy if you adjust the offset manually.
For many requirements this is satisfactory....
Does anyone know if there are any mass market USB GPS devices which *do*
have a PPS pulse? This potentially gets the accuracy down to a few ms
without needing a manual offset correction? Having scanned the options
I don't see any which do this? I accept that USB PPS would be poor by
the standards of other PPS options, but sometimes something is better
than nothing...
The sure evaluation board has usb output and has a PPS (but you need to wire
it up to something.) You could route the pps to the serial port, or even a
parallel port, or anything else that interrupts the computer.
I do not know how the serial to usb converters operate or if they do do
somthing with teh interrupts on the control lines.
Cheers
Ed W
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William G. Unruh | Canadian Institute for| Tel: +1(604)822-3273
Physics&Astronomy | Advanced Research | Fax: +1(604)822-5324
UBC, Vancouver,BC | Program in Cosmology | unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 | and Gravity | www.theory.physics.ubc.ca/
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