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
 
www.madlabs.info
 
----- Original Message -----
From:=20 Bobhelenmcclure@....... =
To: psn-l@..............
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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