SC's USB Clock

D

Dave Goldfinch

Guest
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?

Dave G
 
Dave Goldfinch wrote:
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?

Dave G
Click to expand...
"Network Time Protocol". NTP has the ability to synchronize computers
across multiple time servers while compensating for network jitter and
other statistical errors. Because of this ability, it is generally
suitable for the synchronization of a corporate time server to an atomic
clock on the global internet to within tens of milliseconds. This
protocol is defined in the Internet standard RFC 1305.
 
"Dave Goldfinch" <daveg50_8@NotCoolMail.invalid> wrote in message
news:t9oge4t14orlbshudf4cvi9o3h8umahjkf@4ax.com...
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?

Dave G
Click to expand...
Any errors from network delays will only last till the next synch and if
they are small will not matter.
A 2 seconds a day error will be 1 minute a month because that error is
cumulative.

John G.
 
John G wrote:
"Dave Goldfinch" <daveg50_8@NotCoolMail.invalid> wrote in message
How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?
Any errors from network delays will only last till the next synch and if
they are small will not matter.
Click to expand...
That's not how it work. Many network packets are sent to try to
establish the latency and the variance, and the measured cumulative
errors are used to form a corrective prediction against the local
clock.

The network latency can be in the hundreds of milliseconds yet the
result can be more accurate than that.
 
Davo wrote:

Dave Goldfinch wrote:
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?

Dave G

"Network Time Protocol". NTP has the ability to synchronize computers
across multiple time servers while compensating for network jitter and
other statistical errors. Because of this ability, it is generally
suitable for the synchronization of a corporate time server to an atomic
clock on the global internet to within tens of milliseconds. This
protocol is defined in the Internet standard RFC 1305.
Click to expand...
Yupe, NTP is apparently not all that accurate - it seems that, sometimes,
even under the best possible conditions, it can still be out by as much as
232 picoseconds :) So if you are planning to launch your own space shuttle
flight from your backyard to some nearby galaxy, you have been warned - you
could end up somewhere entirely different. :)
 
Moses Lim wrote:
Davo wrote:

Dave Goldfinch wrote:
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?

Dave G
"Network Time Protocol". NTP has the ability to synchronize computers
across multiple time servers while compensating for network jitter and
other statistical errors. Because of this ability, it is generally
suitable for the synchronization of a corporate time server to an atomic
clock on the global internet to within tens of milliseconds. This
protocol is defined in the Internet standard RFC 1305.

Yupe, NTP is apparently not all that accurate - it seems that, sometimes,
even under the best possible conditions, it can still be out by as much as
232 picoseconds :) So if you are planning to launch your own space shuttle
flight from your backyard to some nearby galaxy, you have been warned - you
could end up somewhere entirely different. :)
Click to expand...
The directional booster nozzles on my craft will easily account for such
minor time errors.
 
On Oct 5, 7:28 pm, "John G" <gr...@ozemail.com.au> wrote:
"Dave Goldfinch" <daveg5...@NotCoolMail.invalid> wrote in message

news:t9oge4t14orlbshudf4cvi9o3h8umahjkf@4ax.com...

This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?

Dave G

Any errors from network delays will only last till the next synch and if
they are small will not matter.
A 2 seconds a day error will be 1 minute a month because that error is
cumulative.
Click to expand...
It's not cumulative if you re-synchronise, that's the point of it.

Dave.
 
Davo wrote:
The directional booster nozzles on my craft will easily account for such
minor time errors.
Click to expand...

You can't go, unless you're willing to take Phil back to his home
world.


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On Oct 5, 4:57 pm, Dave Goldfinch <daveg5...@NotCoolMail.invalid>
wrote:
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?
Click to expand...
As others have pointed point, latency isn't really a problem.

From a practical point of view though it's a fairly useless project.
For starters it's got no seconds display, USB sync is such a pain that
no one will bother (unless you sit on your desk next to the computer),
and who is going to want a hand held project box like that as a
feature clock anyway?
It's really just a demonstration project rather than being of any
practical worth. Nothing wrong with that though I suppose.

Dave.
 
"Davo" <Dave@gmail.com> wrote in message
news:48e9820a_6@news.peopletelecom.com.au...
Yupe, NTP is apparently not all that accurate - it seems that,
sometimes,
even under the best possible conditions, it can still be out by as much
as
232 picoseconds :) So if you are planning to launch your own space
shuttle
flight from your backyard to some nearby galaxy, you have been warned -
you
could end up somewhere entirely different. :)

The directional booster nozzles on my craft will easily account for such
minor time errors.
Click to expand...
Just as they do for NASA. I sure can't imagine them trying to time a launch
to 232 picoseconds either :)

MrT.
 
On Sun, 5 Oct 2008 19:05:47 -0700 (PDT), "David L. Jones"
<altzone@gmail.com> wrote:

On Oct 5, 4:57 pm, Dave Goldfinch <daveg5...@NotCoolMail.invalid
wrote:
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?

As others have pointed point, latency isn't really a problem.

From a practical point of view though it's a fairly useless project.
For starters it's got no seconds display, USB sync is such a pain that
no one will bother (unless you sit on your desk next to the computer),
and who is going to want a hand held project box like that as a
feature clock anyway?
It's really just a demonstration project rather than being of any
practical worth. Nothing wrong with that though I suppose.

Dave.
Click to expand...

Well, thanks for the clarification guys.

I must admit I agree with DLJ - I can't really see this as a really
practical project - if you really had a need for that sort of accuracy
you would be better off building the GPS referenced clock from a few
months ago.

Dave G.
 
On Sun, 05 Oct 2008 19:05:47 -0700, David L. Jones wrote:


It's really just a demonstration project rather than being of any
practical worth. Nothing wrong with that though I suppose.
Click to expand...
Does it teach basic internet service stuff?
aka go to this ipand read this port?
 
On Oct 6, 11:34 pm, terryc <newssixspam-s...@woa.com.au> wrote:
On Sun, 05 Oct 2008 19:05:47 -0700, David L. Jones wrote:
It's really just a demonstration project rather than being of any
practical worth. Nothing wrong with that though I suppose.

Does it teach basic internet service stuff?
aka go to this ipand read this port?
Click to expand...
It's billed as a project "for the advanced constructor"
Part 1 this month is all about the surface mount soldering.
Next month they tell you how to synchronise it and run the
USBCLOCK.EXE program every time your PC starts.
Sounds like it's a two step process - synchronise your PC clock and
then the USB clock is programed from your PC time.

Dave.
 
On Oct 6, 10:54 pm, Dave Goldfinch <daveg5...@NotCoolMail.invalid>
wrote:
On Sun, 5 Oct 2008 19:05:47 -0700 (PDT), "David L. Jones"



altz...@gmail.com> wrote:
On Oct 5, 4:57 pm, Dave Goldfinch <daveg5...@NotCoolMail.invalid
wrote:
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?

As others have pointed point, latency isn't really a problem.

From a practical point of view though it's a fairly useless project.
For starters it's got no seconds display, USB sync is such a pain that
no one will bother (unless you sit on your desk next to the computer),
and who is going to want a hand held project box like that as a
feature clock anyway?
It's really just a demonstration project rather than being of any
practical worth. Nothing wrong with that though I suppose.

Dave.

Well, thanks for the clarification guys.

I must admit I agree with DLJ - I can't really see this as a really
practical project - if you really had a need for that sort of accuracy
you would be better off building the GPS referenced clock from a few
months ago.
Click to expand...
Or at least something more practical in terms of looks and syncing.
e.g. a mantel style clock with automated direct time sync via Ethernet
or wireless.
Kinda like this one:
http://www.circuitcellar.com/microchip2007/winners/second.html

I'd be surprised if any of the kit suppliers carry it.

Dave.
 
Dave Goldfinch wrote:
On Sun, 5 Oct 2008 19:05:47 -0700 (PDT), "David L. Jones"
altzone@gmail.com> wrote:

On Oct 5, 4:57 pm, Dave Goldfinch <daveg5...@NotCoolMail.invalid
wrote:
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?
As others have pointed point, latency isn't really a problem.

From a practical point of view though it's a fairly useless project.
For starters it's got no seconds display, USB sync is such a pain that
no one will bother (unless you sit on your desk next to the computer),
and who is going to want a hand held project box like that as a
feature clock anyway?
It's really just a demonstration project rather than being of any
practical worth. Nothing wrong with that though I suppose.

Dave.


Well, thanks for the clarification guys.

I must admit I agree with DLJ - I can't really see this as a really
practical project - if you really had a need for that sort of accuracy
you would be better off building the GPS referenced clock from a few
months ago.

Dave G.
Click to expand...
I work in a power station that uses some very large and widely
distributed control systems. We use a GPS device for timing, however I
can see that in other industrial situations a project like this would be
suitable for a master time system.
 
On Oct 7, 12:20 pm, Davo <D...@gmail.com> wrote:
Dave Goldfinch wrote:
On Sun, 5 Oct 2008 19:05:47 -0700 (PDT), "David L. Jones"
altz...@gmail.com> wrote:

On Oct 5, 4:57 pm, Dave Goldfinch <daveg5...@NotCoolMail.invalid
wrote:
This project is supposed to synchronise with the Internet via a PC to
ensure "accurate timekeeping"

How accurate can it be, when any time signal derived via the internet
will be delayed by the unpredictable latency of the network ?

The claimed accuracy in stand alone mode, running off a watch crystal
is 2 seconds a day. Are you really going to improve it by a daily
sync with the net ? I would have thought that all you will achive will
be to keep the clock in step with your PC and the net service from
which the PC's time is derived +/- the latency error.

Any ideas ?
As others have pointed point, latency isn't really a problem.

From a practical point of view though it's a fairly useless project.
For starters it's got no seconds display, USB sync is such a pain that
no one will bother (unless you sit on your desk next to the computer),
and who is going to want a hand held project box like that as a
feature clock anyway?
It's really just a demonstration project rather than being of any
practical worth. Nothing wrong with that though I suppose.

Dave.

Well, thanks for the clarification guys.

I must admit I agree with DLJ - I can't really see this as a really
practical project - if you really had a need for that sort of accuracy
you would be better off building the GPS referenced clock from a few
months ago.

Dave G.

I work in a power station that uses some very large and widely
distributed control systems. We use a GPS device for timing, however I
can see that in other industrial situations a project like this would be
suitable for a master time system.
Click to expand...
Here is another NTP clock project for those playing along at home:
http://tuxgraphics.org/electronics/200710/avr-ntp-clock.shtml
Just plug into your router.

Dave.
 
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