PSN-L Email List Message
Subject: Re: Subject: Re: Atomic Time Source for data logging
From: "Jonathan Peakall" jpeakall@............
Date: Sun, 23 Feb 2003 06:29:04 -0800
Bob, All,
Following Bob's ideas and with his help, I made basically the same =
system. The only difference was I used an photogate of the style that is =
used in floppy drives, and painted the second hand white. Works like a =
champ and is cheap. I put the gate on an arm that pivots on the "hands =
holder", and clamps on the edge of the face for easy adjustment.
Later however, when I was trying to get the actual time and date from =
the unit, I realized how easy it was to pull a direct 1PPS from the =
unit. I then got rid of the photogate and used that to make marks via =
the DATAQ 194-RS. This is much better, no bounce. I eliminated the =
actual clock mechanism, and now the battery lasts forever. Mind you, it =
isn't very useful as a clock anymore! Bob, if you are interested in =
details let me know. It's very simple surgery.
The main reason for going to all the trouble I did for atomic time is I =
wanted to be able to make more than minute marks on my log, and I have a =
number of projects that can use an accurate time base. Since I will have =
at least 4 devices using the timebase, it was a reasonably economical =
solution as well, I have a total of less then US$100 into the atomic =
time broadcast system. A clock chip for all my projects would have been =
about the same or a little less, but then I don't have to use any =
buttons and I/O pins used (except one I/O pin) or use program space on =
time setting routines.
Another reason is the cheap clock I was using didn't link very often to =
WWVB. This is due to my poor reception. The module I am using now is =
much better.
Now all I have to do is weatherize my seismic sensor and get back to =
work on it. The school year is crazy for me, so I hope to get it all set =
up this summer, if I don't have to move.
Regards,
Jonathan
www.madlabs.info
----- Original Message -----=20
From: Bobhelenmcclure@..........
To: psn-l@.................
Sent: Saturday, February 22, 2003 9:52 PM
Subject: Subject: Re: Atomic Time Source for data logging
My nearby seismic buddy and I have established a local area =
tripartite network for the study of microseisms. We record for short =
periods simultaneously at three sites, and require accurate timing of =
the three records in order to calculate time differences of arrival. We =
use Dataq RS-154 and RS-194 digitizers which have a digital input for =
registering time marks on the records. We use WWVB controlled wall =
clocks for generating minute marks.
My buddy uses large LCD RadioShack clocks, and photo-optically looks =
at the lower right segment of the tens-of-seconds digit. This segment =
is black for all digits except for the digit "2," so every minute it =
disappears at 20 seconds past the minute for 10 seconds. His pickup =
circuit has a logic high output whenever the segment is black and low =
when it is absent. The Dataq recorder will make a mark at either of the =
transitions. He uses the high-to-low transitions, so gets minute marks =
20 seconds past the minute.
I use an analog wall clock, brand name "Atomix," distributed by =
Cheney Instruments. I removed the plastic face, glued a . 25-inch =
circle of aluminum foil reflector to the sweep second hand, and replaced =
the face. The pickoff is held in place by a rubber band and string, and =
is positioned on the clock face to detect the second hand when it is at =
the even minute. The pickoff circuitry is mounted in a wooden block, =
painted black. The light source is a red LED and the detector is a =
phototransistor, coupled to a medium-gain NPN transistor. There are =
some potential problems with this scheme. For one thing, the clock goes =
through an adjustment procedure every few hours to synchronize with =
WWVB. It starts running fast and then slows down to fall into alignment =
with the radio signal. Except for the few minutes when this is going =
on, the clock is very accurate. Another potential problem is that the =
second hand does not simply jump from one second to the next, but =
overshoots before settling down. The pickoff must be carefully =
positioned to avoid sensing the bounce from second 59 and well as the =
dwell at second zero. I purchased two of these clocks from =
HeartlandAmerica, and one of them had too much bounce to be useful.
We have tested both marking schemes at the same site on a single =
digitizer, and have determined that there is no detectable differences =
in our timing (except for the fixed 20-second offset.)
With analog wall clocks, it is also possible to generate one-second =
marks by inductively picking up the clock's stepper motor's current =
pulse.
If anyone is interested in trying the above schemes, I will be happy =
to give further details.
Bob McClure=20
Bob, All,
Following Bob's ideas and with his =
help, I made=20
basically the same system. The only difference was I used an photogate =
of the=20
style that is used in floppy drives, and painted the second hand white. =
Works=20
like a champ and is cheap. I put the gate on an arm that pivots on the =
"hands=20
holder", and clamps on the edge of the face for easy =
adjustment.
Later however, when I was =
trying to get=20
the actual time and date from the unit, I realized how easy it was to =
pull a=20
direct 1PPS from the unit. I then got rid of the photogate and used that =
to make=20
marks via the DATAQ 194-RS. This is much better, no bounce. I eliminated =
the=20
actual clock mechanism, and now the battery lasts forever. Mind you, it =
isn't=20
very useful as a clock anymore! Bob, if you are interested in details =
let me=20
know. It's very simple surgery.
The main reason for going to all the =
trouble I did=20
for atomic time is I wanted to be able to make more than minute marks on =
my log,=20
and I have a number of projects that can use an accurate time base. =
Since I will=20
have at least 4 devices using the timebase, it was a reasonably =
economical=20
solution as well, I have a total of less then US$100 into the atomic =
time=20
broadcast system. A clock chip for all my projects would have been about =
the=20
same or a little less, but then I don't have to use any buttons and =
I/O=20
pins used (except one I/O pin) or use program space on time =
setting=20
routines.
Another reason is the cheap clock I was =
using=20
didn't link very often to WWVB. This is due to my poor reception. The =
module I=20
am using now is much better.
Now all I have to do is weatherize my =
seismic=20
sensor and get back to work on it. The school year is crazy for me, so I =
hope to=20
get it all set up this summer, if I don't have to move.
Regards,
Jonathan
----- Original Message -----
Sent: Saturday, February 22, =
2003 9:52=20
PM
Subject: Subject: Re: Atomic =
Time Source=20
for data logging
My nearby seismic buddy and I have =
established a=20
local area tripartite network for the study of microseisms. We =
record=20
for short periods simultaneously at three sites, and require accurate =
timing=20
of the three records in order to calculate time differences of =
arrival. =20
We use Dataq RS-154 and RS-194 digitizers which have a digital input =
for=20
registering time marks on the records. We use WWVB controlled =
wall=20
clocks for generating minute marks.
My buddy uses large =
LCD=20
RadioShack clocks, and photo-optically looks at the lower right =
segment of the=20
tens-of-seconds digit. This segment is black for all digits =
except for=20
the digit "2," so every minute it disappears at 20 seconds past the =
minute for=20
10 seconds. His pickup circuit has a logic high output whenever =
the=20
segment is black and low when it is absent. The Dataq recorder =
will make=20
a mark at either of the transitions. He uses the high-to-low=20
transitions, so gets minute marks 20 seconds past the =
minute.
I=20
use an analog wall clock, brand name "Atomix," distributed by Cheney=20
Instruments. I removed the plastic face, glued a . 25-inch =
circle of=20
aluminum foil reflector to the sweep second hand, and replaced the =
face. =20
The pickoff is held in place by a rubber band and string, and is =
positioned on=20
the clock face to detect the second hand when it is at the even =
minute. =20
The pickoff circuitry is mounted in a wooden block, painted =
black. The=20
light source is a red LED and the detector is a phototransistor, =
coupled to a=20
medium-gain NPN transistor. There are some potential problems =
with this=20
scheme. For one thing, the clock goes through an adjustment =
procedure=20
every few hours to synchronize with WWVB. It starts running fast =
and=20
then slows down to fall into alignment with the radio signal. =
Except for=20
the few minutes when this is going on, the clock is very =
accurate. =20
Another potential problem is that the second hand does not simply jump =
from=20
one second to the next, but overshoots before settling down. The =
pickoff=20
must be carefully positioned to avoid sensing the bounce from second =
59 and=20
well as the dwell at second zero. I purchased two of these =
clocks from=20
HeartlandAmerica, and one of them had too much bounce to be=20
useful.
We have tested both marking schemes at the same =
site on=20
a single digitizer, and have determined that there is no detectable=20
differences in our timing (except for the fixed 20-second=20
offset.)
With analog wall clocks, it is also possible to =
generate one-second marks by inductively picking up the clock's =
stepper=20
motor's current pulse.
If anyone is interested in trying =
the=20
above schemes, I will be happy to give further details.
Bob=20
McClure
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