Or, happy thought, simply use a pointer laser at the target end, triggered
by the target chrono, and received at the bench chronograph. Simple, and the
remote stop pulse easy to pick up with simple optics. Heck, use an old
scope. Shoulda thought of that first.
Even a picaxe will give you sufficient accuracy, and the 18x has an IR
input.
Don
----- Original Message -----
From: "Don Latham" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Sent: Monday, November 01, 2010 11:34 PM
Subject: Re: [time-nuts] A real world project need for timing accuracy...
I guess i don't understand. If you start a counter with the start pulse
from the local chrono, and send back a stop pulse from the start pulse of
the distant chron over the zigbee link using an interrupt on the distant
controller, the response time can be subtracted. Simple calibration of the
electronics delay should be measureable?
Don
----- Original Message -----
From: "Hal Murray" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Sent: Monday, November 01, 2010 10:10 PM
Subject: Re: [time-nuts] A real world project need for timing accuracy...
[email protected] said:
However, time-of-flight info (via an RF link requires
that I sync the 10MHz clocks at both ends together.
Use of GPS receivers seems to be the most likely way
to do this but how do I keep the cost and complexity
down?
What level of accuracy do you need?
I think GPS will do what you want. You can get one of the
mouse/hockey-puck
units for well under $100. I think you need one at each end so that
doubles
the cost. Be sure to avoid the USB units because they don't have PPS
signals.
Option 2: How long can you coast? (holdover mode) If your crystal is
off
by 1E-6 and you coast for 1000 seconds, you will be off by 1 ms. Is that
good enough? You can get better accuracy with better hardware and/or
better
software. By software I mean 1) correcting for the initial calibration
error, and 2) correcting for the temperature. [It would be fun to see
what
you could do starting with an inexpensive oscillator package.] You can
double-check and/or get more data for correction if you bring the unit
back
to the base station at the end of the run and see how far it has drifted.
Option 3: Use a bi-directional RF link. Send a "PPS" signal to the gear
at
the target. I think you will have to calibrate out the delays through
the RF
links but that should be simple if you assume symmetry.
What sort of RF gear are you considering? Are the normal units both
transmit
and receive, or do you have to buy another pair for the other direction?
Option 4: Send the PPS signal upstream and compensate for the clock drift
at
the upstream end. Again, I think you may have to calibrate for the
delays
through the RF link which may vary slightly with distance and antenna
setup.
PS: How accurately do you measure the distance?
--
These are my opinions, not necessarily my employer's. I hate spam.
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