Graham,
I think that is the real challenge here: most folks don't know what
"precise" means for them. Timing is such a novel technology that most folks are
amazed that we are trying to get parts per trillion (or better) accuracy and
stability!
We get customers all the time that want very precise timing, very good
phase noise, and overall very good performance but are only used to TCXO's with
maybe 10ppm frequency accuracy and cannot specify anything beyond that.
The challenge is to explain the cost-benefit to them, like:
1ppm == $1
0.01ppm = $300
10ppt == $1500
0.1ppt == $$$ etc.
Once dollars are mentioned, desired specifications usually are attained at
fairly quickly :)
We recently had an inquiry that we forwarded to a major atomic oscillator
vendor, and the estimated $10 Million design cost and 10 year design time
quickly shut that idea down..
bye,
Said
In a message dated 7/12/2014 08:54:09 Pacific Daylight Time,
gh78...@gmail.com writes:
Shane:
The question I think that is being asked is ...
What does "precise" mean to you?
To the nearest order of magnitude, what kind of accuracy are you looking
for
on your three signals. This defines the kind of system you will need.
This group normally aspires to the more accurate end of the scale.
If you are doing simple time logging of some process, then you are
probably at the other end of the possible accuracy scale, and can
do things much more simply and cheaply.
So ...
1 PPS: +/- 1 ns? 10 ns? 100 ns? 1 us? 10 us ?
NTP: +/- 10 ms? 100 ms? 1 second?
10 MHz: +/- 10E-6? 10E-9? 10E-12? 10E-14?
--- Graham
==
On Sat, Jul 12, 2014 at 3:57 AM, Shane Morris <edgecombe...@gmail.com>
wrote:
Hal,
As much as I'd like to explain the "big picture" in list, it would make
God
awful noise - if you wish to know any details, I encourage you to respond
to me off list. Given the fact that the robotics is so totally off topic,
I'm not willing to discuss them here. Thats only out of respect to the
topic of the list. The only real stipulations at this design part of the
project is 10MHz out, 1PPS out, and NTP out. Please don't think I'm being
narqy, I'm really not going to pollute the list with off topic chatter. I
am more than happy to discuss off list, as and when.
David,
I was planning to use RaspberryPis in some part of the network, and of
course, I must be silly, they have ethernet, and can run Real Time Linux
(the LinuxCNC distros that have been made for control of CNC machines).
By
the way, the whole network uses heterogeneous CPU types, I'm pretty
agnostic to CPU type, as long as it does the job I need it to. The actual
ethernet interface won't be as deterministic as we'd like, being chained
to
the USB bus, but if one was not to put any other USB devices on, nor
attach
anything that draws power, the USB performance would be good enough for
second accuracy NTP frames. This is without any real analysis of any spec
sheets, although I have this link:
http://www.synclab.org/?tag=raspberry%20pi
Thats an interesting read in and of itself. An additional link is:
http://www.geekroo.com/products/795
Which is a Mini ITX motherboard for RaspberryPi, which can then go nicely
into a 1RU case. Add LCDs and other bits and bobs as needed (I saw a nice
little LCD with an ATMega driver taking TTY strings in the ODROID
Magazine
earlier today - it was meant for an ODROID, but it will work with
anything
that'll output VT100 codes). Once in an 1RU case, it looks neat, and
would
work just as well as a $500 NTP ethernet time source second hand off
eBay,
if not much more configurable and hackable.
Many thanks for the thoughts!
Shane.
On Sat, Jul 12, 2014 at 5:50 PM, Hal Murray <hmur...@megapathdsl.net>
wrote:
> edgecombe...@gmail.com said:
I am needing a GPS source of precise time, in three flavours - 10MHz
(or
so), 1PPS, and ethernet NTP. In the beginning, the NTP will be most
> important, and as time goes on, I'll need the 1PPS signal.
...
If a static CW12-TIM ethernet clock could be made, I would be willing
to
try
my hand at mounting them to mobile robots, again, for synchronised
timing of
events.
I'm missing the big picture. Are the robots the end target? What are
you
going to do before that?
Do the robots have a network connection? (maybe only WiFi to a local
PC
> controlling them)
How accurately do the robots have to be synchronized?
--
> These are my opinions. I hate spam.
>
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