LED alarm clocks all lose accuracy over time

[Geoffrey S. Mendelson]

Bill Proms wrote:

As a possible replacement, I have considered an atomic LED clock, but these
appear to be next to impossible to come by for some reason. I see LCD
atomic clocks everywhere, but most or all have to have the backlight pressed
to see the time in dim conditions.

It's because the US is trying to get rid of those broadcasts. With GPS they
are obsolete.

Geoff.

--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(

 

[Ian Field]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:jp8p22$8i8$1@dont-email.me...

Jeff Liebermann <jeffl@cruzio.com> wrote in message
news:h9dfr71u6fchkgccmmpjd31m95ifn47s6k@4ax.com...
On Sat, 19 May 2012 07:53:46 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net> wrote:

I once modified a vacuum fluorescent alarm clock to keep accurate
time. I opened the device, figured out what chip was used, looked at
the data sheet, and replaced the crappy RC oscillator with a 32KHz
clock crystal. When the AC power disappears, the display goes blank
and the internal 9v battery runs the clock. The problem is that the
battery drain was so high that it would kill the 9V battery in about 6
hrs. There was also no charging circuit. So, I replaced the 9V
battery with 4ea AA NiCd batteries (the clock chip would still run on
about 6VDC), and added a crude trickle charger.

The world's first clock-radio with an all-electronic digital clock -- a
GE,
which I still have, 40 years after I bought it (!!!) -- used a
nicad-powered
oscillator running at ~ 60Hz to keep the timer going. I don't think it
ran
more than about 10 minutes.

I think I remember seeing those. Todays version will last about a
year before something blows or it falls apart. Progress?

Way back in college daze (1960's), one of my friends was trying to
devise a method of running a motor drive electric clock during power
outages. I designed a line sync blocking oscillator, that ran in sync
with the 60Hz power line frequency when that was present, but ran off
battery power at roughly 60Hz when that disappeared. To get
sufficient power to run the clock, it had two 2N3055 transistors
playing push-pull oscillator to a small power transformer. It was
big, noisy, and ugly, but worked quite well. Keeping the wet cell
battery charged was the major challenge. We were thinking of
manufacturing these, but was talked out of the idea by someone with
more marketing sense than us.

The analog wall clocks in high skool were all wired to central time
controller. Curious as to how it worked, I dragged an oscilloscope
into the main hallway to clip onto the only accessible wires I could
find. Every 15 minutes, a sync pulse would appear on the line,
resetting the clocks to the nearest 15 minutes. Every hour, two
pulses would reset the clocks to the nearest hour. At noon and
midnight, 5 pulses would reset the clocks to midnight. Unfortunately,
gathering this intelligence required almost constant monitoring, which
attract too much attention. I was caught before I could make the
clocks run backwards. Not a great start for my first attempt at
hacking.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558



I used to "wind-up" my father by stopping the synchronus-motor clock and
with a bit of backwards pressure on the seconds hand , while turning the
power back on , the clock would go backwards

............then some smart-arse invented the shaded pole motor.

 

[Geoffrey S. Mendelson]

Bill Proms wrote:

Yes, there are power interruptions and surges on occasion, but the former
LED clocks I had never lost time over periods of years.

As a possible replacement, I have considered an atomic LED clock, but these
appear to be next to impossible to come by for some reason. I see LCD
atomic clocks everywhere, but most or all have to have the backlight pressed
to see the time in dim conditions.

The real answer which has yet to be rolled out to consumers is to use NTP
(networked time protcol) self correcting clocks. They basically are are
cheap router with a single ethernet and wifi interfaces, and a display.
All of them already run NTP, it's a matter of adding the time display,
changing the setup to limit them to things needed to connect to the internet
and set the clock and repackaging them.

Figure a consumer price for the cheap ones of around $25-$30 and another
$10 for self setting GPS one.

Geoff.

--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(

 

[Jeff Liebermann]

On Sat, 19 May 2012 14:31:48 -0500, Jim Yanik <jyanik@abuse.gov>
wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote in
I once modified a vacuum fluorescent alarm clock to keep accurate
time. I opened the device, figured out what chip was used, looked at
the data sheet, and replaced the crappy RC oscillator with a 32KHz
clock crystal. When the AC power disappears, the display goes blank
and the internal 9v battery runs the clock. The problem is that the
battery drain was so high that it would kill the 9V battery in about 6
hrs. There was also no charging circuit. So, I replaced the 9V
battery with 4ea AA NiCd batteries (the clock chip would still run on
about 6VDC), and added a crude trickle charger.

was that a 32KHz crystal,or a 32KHz ceramic resonator?

Neither. It was a junk RC oscillator. Just a resistor and capacitor.
There was a reference designator on the PCB showing a ceramic
resonator, but what was installed was a resistor and a capacitor. My
replacement was a common 32KHz crystal that I found in my junk box.

I suspect it's the latter.that would explain the poor freq.stability.
You can trim up an XTAL oscillator.

Ceramic resonators aren't all that horrible and can also be tuned.
I've used plenty (usually Murata) for IF filters in radio designs at
455KHz and 10.7MHz. I will admit to matching them by frequency (bin
test) rather than deal with tuning and tweaking.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Sat, 19 May 2012 21:20:26 +0100, "Ian Field"
<gangprobing.alien@ntlworld.com> wrote:

Incidentally, I'm building my own 10MHz GPSDO for running my test
eqipment and ham junk. It's NOT a trivial or inexpensive exercise:

A while back (I think it was) EPE magazine (or might have been Elektor)
published a GPS frequency standard generator projects.

There are plans all over the internet. Almost all of them use the
Rockwell Jupiter board, which has a convenient 10KHz output. That
would normal be the way to go, except that I have a large pile of
Novatel Allstar 12 boards, which have 1Hz and 10Hz outputs. That
makes the design somewhat more complicated.

Its available as a kit, so although not particularly cheap it is fairly
easy.

Complete GPSDO modules can be found for about $300.
<http://www.navsync.com/GPS_timing.html>
<http://www.navsync.com/docs/CW46_prod_brief.pdf>
I'm building mine much the same way, with integrated antenna, etc.

The 1pps output can be used to run a digital clock, but I would hate
to see the final cost.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[William Sommerwerck]

Many years ago I reviewed Heath's "Most-Accurate Clock" for one of Ed Dell's
magazines. It used the Bureau of Standards' shortwave time signals. Sync was
a bit touchy (I eventually replaced the carbon calibration pots with
ceramic), but it otherwise worked very well. It even had an interface that
allowed your computer to reset its clock each time the machine restarted.

When I needed money a few years back, I sold it on eBay for something like
$400, without anyone questioning the price.

If Heath wants to come back as a kit company, it needs to design products
that have no commercial equivalents.

 

[Geoffrey S. Mendelson]

Jeff Liebermann wrote:

The 1pps output can be used to run a digital clock, but I would hate
to see the final cost.

We are talking about a clock here, something most people are to seeing
display hours and minutes. Few of them have seconds. None have 10ths,
hundreds, etc.....

While an NTP interface with wifi would do for probably 90% of the world,
the few people that don't have any internet access, would need a GPS unit.

If you can get one in a cheap cell phone these days, how much would it cost
to put in a clock? I understand that it won't give you milisecond accuracy,
but a window view that can "see" 3 or 4 satellites (or an outside antenna
would do.

However, I'd happily buy 5 or 6 of them with wifi. I'm tired of battery
run analog or even line operated digital clocks ones that are off several
minutes a week.

Yes, they have a design flaw, but I can't return them after they start
showing the time gain or loss, it takes too long to show up.

Geoff.

--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(

 

[micky]

On Sat, 19 May 2012 08:51:38 -0400, "Bill Proms" <none@anywhere.us>
wrote:

I have 3 Intelli-Time LED alarm clocks around the house, just like the one
here:

I don't think the LEDs are causing the problem.

http://www.acurite.com/clock/alarm-clock/intelli-time-digital-alarm-clock-13027a2.html

I initially bought these due to them keeping time when the power goes off
and auto resetting for DST. There is a problem, however. Each of the
clocks becomes inaccurate over time. If I set them all manually to the same
time, within a few months, each one will be off by 3-5 minutes.

So I ask, what is the problem and is there any way to repair it?

If it's based on a quartz crystal, you could shave a little quartz off
the big piece, or sand it off, or attach some more, depending on if
the clock is slow or fast.

Thanks in advance,
Bill

Just kidding.

 

[gregz]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

Many years ago I reviewed Heath's "Most-Accurate Clock" for one of Ed Dell's
magazines. It used the Bureau of Standards' shortwave time signals. Sync was
a bit touchy (I eventually replaced the carbon calibration pots with
ceramic), but it otherwise worked very well. It even had an interface that
allowed your computer to reset its clock each time the machine restarted.

When I needed money a few years back, I sold it on eBay for something like
$400, without anyone questioning the price.

If Heath wants to come back as a kit company, it needs to design products
that have no commercial equivalents.

Heath had an fm tuner with direct frequency entry push button. I never saw
another for home use, but there may have been another or commercial use.

Around about 1974, bought my first led clock, and first calculator. The
clock, cubo, from js&a was unique. Had separate buttons for hours, seconds,
etc. You turned it upside down for snooze.

Greg

 

[Klaatu]

"Bill Proms" <none@anywhere.us> wrote in message
news:jp850p$fk2$1@dont-email.me...

I have 3 Intelli-Time LED alarm clocks around the house, just like the one
here:

http://www.acurite.com/clock/alarm-clock/intelli-time-digital-alarm-clock-13027a2.html

I initially bought these due to them keeping time when the power goes off
and auto resetting for DST. There is a problem, however. Each of the
clocks becomes inaccurate over time. If I set them all manually to the
same time, within a few months, each one will be off by 3-5 minutes.

So I ask, what is the problem and is there any way to repair it?

Thanks in advance,
Bill

http://www.ebay.com/itm/Westclox-70026A-LCD-Atomic-Digital-Alarm-Clock-/261019821915?pt=LH_DefaultDomain_0&hash=item3cc5fe675b

or, if you want to see the display at night

http://www.ebay.com/itm/Atomic-Projection-Alarm-Clock-/310396561330?pt=US_Clocks&hash=item484513a7b2

I've used one of the projection alarm clocks for 4 years now, with the
projector light on 24/7.
No problems. Its has battery back-up, but no projection if the power fails.
All the alarm and wall clocks in the house are now atomic. So is my
wristwatch.
IMHO, If a clock doesn't show the correct time, its not a clock...its a
timer.

 

[Jim Yanik]

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:0jvfr79mm8osvjt6k651q09lngv9fla5go@4ax.com:

On Sat, 19 May 2012 14:31:48 -0500, Jim Yanik <jyanik@abuse.gov
wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote in
I once modified a vacuum fluorescent alarm clock to keep accurate
time. I opened the device, figured out what chip was used, looked at
the data sheet, and replaced the crappy RC oscillator with a 32KHz
clock crystal. When the AC power disappears, the display goes blank
and the internal 9v battery runs the clock. The problem is that the
battery drain was so high that it would kill the 9V battery in about 6
hrs. There was also no charging circuit. So, I replaced the 9V
battery with 4ea AA NiCd batteries (the clock chip would still run on
about 6VDC), and added a crude trickle charger.

was that a 32KHz crystal,or a 32KHz ceramic resonator?

Neither. It was a junk RC oscillator. Just a resistor and capacitor.
There was a reference designator on the PCB showing a ceramic
resonator, but what was installed was a resistor and a capacitor. My
replacement was a common 32KHz crystal that I found in my junk box.

I suspect it's the latter.that would explain the poor freq.stability.
You can trim up an XTAL oscillator.

Ceramic resonators aren't all that horrible and can also be tuned.
I've used plenty (usually Murata) for IF filters in radio designs at
455KHz and 10.7MHz. I will admit to matching them by frequency (bin
test) rather than deal with tuning and tweaking.

an IF filter has a wider BW than what you want for an osc.
Xtal gives a beter freq stability,because of it's sharper BW and high Q.
you don't see ceramic resonators in freq. standards.

Also,32KHz xtals aren't the best freq standards.
1-10 Mhz are the usual ones used for standards,better stability.

--
Jim Yanik
jyanik
at
localnet
dot com

 

[Jim Yanik]

"Ian Field" <gangprobing.alien@ntlworld.com> wrote in
news:9bTtr.549288$yJ4.364502@fx07.am4:

"gregz" <zekor@comcast.net> wrote in message
news:1124369627359136873.854687zekor-comcast.net@news.eternal-september
.org...
"N_Cook" <diverse@tcp.co.uk> wrote:
Bill Proms <none@anywhere.us> wrote in message
news:jp850p$fk2$1@dont-email.me...
I have 3 Intelli-Time LED alarm clocks around the house, just like
the one
here:


http://www.acurite.com/clock/alarm-clock/intelli-time-digital-alarm-c
lock-13 027a2.html

I initially bought these due to them keeping time when the power
goes off
and auto resetting for DST. There is a problem, however. Each of
the clocks becomes inaccurate over time. If I set them all
manually to the
same
time, within a few months, each one will be off by 3-5 minutes.

So I ask, what is the problem and is there any way to repair it?

Thanks in advance,
Bill



I've always put this down to hash on the mains being interpreted as
extra cycles by the clock monitoring input. The supply companies
contractually have to correct the mains frequency so an exact number
of cycles per day (50/60)x60x60x24, but at any instant can be above
or below the nominal frequency.

I doubt if any use power line for sync. Most have battery backup.
Crystals jump frequency from time to time.


Even one I bought recently uses mains sync, but it has a battery &
crystal divider backup to cover outages.

The mains frequency varies depending on peak demand/off peak, but long
term its average has less drift than the cheap crystal oscillator
they're going to put in a radio alarm clock.

radio alarm clock probably won't even use an xtal;like Jeff L. says,they
may use a cheap RC osc.

I note my MW oven clock that derives it's clock from line freq. has better
stability than other "digital" clocks.(like my PC clock....)

(of course,I use an internet program to keep the PC clock fairly close. I
used to use a program(Atomic Clock) that direct-dialed the Naval
Observatory,but the long distance calls cost too much.)

--
Jim Yanik
jyanik
at
localnet
dot com

 

[Jeff Liebermann]

On Sat, 19 May 2012 21:39:04 +0000 (UTC), "Geoffrey S. Mendelson"
<gsm@mendelson.com> wrote:

Jeff Liebermann wrote:

The 1pps output can be used to run a digital clock, but I would hate
to see the final cost.

We are talking about a clock here, something most people are to seeing
display hours and minutes. Few of them have seconds. None have 10ths,
hundreds, etc.....

1pps is one pulse every seconds. A second hand is quite common and
useful.

While an NTP interface with wifi would do for probably 90% of the world,
the few people that don't have any internet access, would need a GPS unit.

I've watched several "wired home" type projects flounder and
eventually fail. I'm still somewhat optimistic, but not much. One of
my friends bought a refrigerator that's connected to the internet via
wi-fi.
<http://en.wikipedia.org/wiki/Internet_refrigerator>
He thinks it's cool. His wife hates it and hangs a towel over the
display. I saw much the same reaction as I watched the fully
automatic microwave oven fail miserably. It's going to be a while
before we have a wired (or wireless) home.

If you can get one in a cheap cell phone these days, how much would it cost
to put in a clock? I understand that it won't give you milisecond accuracy,
but a window view that can "see" 3 or 4 satellites (or an outside antenna
would do.

Not too expensive using a SONET GPS chip, which has a convenient 1pps
output:
<http://www.analog.com/pr/AD9548>
<http://www.analog.com/en/press-release/6_11_09_Clock_IC_First_to_Harness_GPS/press.html>
For a commodity alarm clock, the chip does not need to be powered
continuously. Wake it up a few times per hour, grab the time, update
the alarm clock, and go back to sleep. A WWVB 60KHz clock is cheaper,
but a GPS clock is "cool".

Note that you do NOT need to see 3 or 4 birds. You need that if you
want a lat-long-altitude position fix, but only one bird is needed for
the time, which is sent by all the birds as part of the almanac.
<http://en.wikipedia.org/wiki/GPS_signals#Almanac>

However, I'd happily buy 5 or 6 of them with wifi.

There are several SBC (single board computah) that will run Linux.
Adding an cheezy dot matrix LCD display and running NTP is fairly
simple.

I'm tired of battery
run analog or even line operated digital clocks ones that are off several
minutes a week.

Well, we could make a wind-up digital clock, but I don't think it will
sell. I gave up wearing a watch long ago and use the clock in my cell
phone or smartphone. Verizon (CDMA) keeps very accurate time.

Yes, they have a design flaw, but I can't return them after they start
showing the time gain or loss, it takes too long to show up.

It might have something to do with the internal construction. I'm
running into the same mid-life mortality issues with cheap weather
stations. The problem is that the old designs used discrete parts,
SMT parts, and packaged devices. These days, the junk from China uses
COB (Chip On Board) construction. The main chip is buried under a
blob of epoxy or other goo. The epoxy has a different coefficient of
thermal expansion as the PCB. It's not much, but over a fair number
of thermal cycles, it will eventually rip the underlying chip apart.
<http://www.empf.org/empfasis/dec04/improve1204.htm>

Geoff.
--

Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Sat, 19 May 2012 23:30:24 +0000 (UTC), gregz <zekor@comcast.net>
wrote:

Heath had an fm tuner with direct frequency entry push button. I never saw
another for home use, but there may have been another or commercial use.

Heath AJ-1510. It may have been the first true digital synthesized FM
tuner.
<http://www.fmtunerinfo.com/AJ-1510a.jpg>
I have one. Besides the keypad, it has 4 slots for preset frequencies
which are programmed with edge notches on a 1x2" paper card. It's a
good sounding tuner and was quite advanced in its day (1972-1975).

Around about 1974, bought my first led clock, and first calculator. The
clock, cubo, from js&a was unique. Had separate buttons for hours, seconds,
etc. You turned it upside down for snooze.

Weird.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Sat, 19 May 2012 19:36:05 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

If you can get one in a cheap cell phone these days, how much would it cost
to put in a clock? I understand that it won't give you milisecond accuracy,
but a window view that can "see" 3 or 4 satellites (or an outside antenna
would do.

Not too expensive using a SONET GPS chip, which has a convenient 1pps
output:
http://www.analog.com/pr/AD9548
http://www.analog.com/en/press-release/6_11_09_Clock_IC_First_to_Harness_GPS/press.html

Oops. Bad choice of chips and much too expensive.
This is more like it:
<http://geoffg.net/GPS_Synchronised_Clock.html>
Unfortunately, GPS boards are still rather pricy:
<http://www.sparkfun.com/search/results?term=gps+&what=products>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[micky]

On Sat, 19 May 2012 20:45:54 -0500, "Klaatu" <whichway@today.org>
wrote:

http://www.ebay.com/itm/Westclox-70026A-LCD-Atomic-Digital-Alarm-Clock-/261019821915?pt=LH_DefaultDomain_0&hash=item3cc5fe675b

or, if you want to see the display at night

http://www.ebay.com/itm/Atomic-Projection-Alarm-Clock-/310396561330?pt=US_Clocks&hash=item484513a7b2

I've used one of the projection alarm clocks for 4 years now, with the
projector light on 24/7.

When my mother was about 80, I bought something simiilar for her, so
she wouldn't have to roll over to see her clock. But I don't think she
much liked the time on the ceiling. Do you use that? I think the
street lights might have made it hard to see. She didn't mind the
street lights.

I got another one at a yard sale, but I've been sleeping on my belly
or side, so I still have a hard time seeing the ceiling. Worse yet,
the radio is distorted, which is probably why it was only a dollar.
(Well it was on my last trip. I meant to try it here where I know
which stations come in right.)

These clocks were not atomic.

I have a second-hand atomic clock too. I use it to set the time on
my DVDR, which supposedly can set it's own time, but doesn't.

The DVDR doesn't work off of NIST but off of some tv station that
carries the time . Last fall the DVDR got off daylight savings time
by itself, but was still wrong on the minutes! How can that be? On
manual, the clock runs fast 20 seconds a week or so, and a friend
bought the next model, Magnavox instead of Philips, and it does the
same thing. On automatic, it's still wrong by 30 or 60 seconds!

(Ohter than this and a couple other problems, it's a good machine, and
the only one under 600 dolllars designed to work off the air, without
cable or satellite.

No problems. Its has battery back-up, but no projection if the power fails.
All the alarm and wall clocks in the house are now atomic. So is my
wristwatch.
IMHO, If a clock doesn't show the correct time, its not a clock...its a
timer.

 

[isw]

In article <XnsA0589DFE52B22jyaniklocalnetcom@216.168.3.44>,
Jim Yanik <jyanik@abuse.gov> wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:2hafr7t16440eur5henfoq8rl2sj9ie9sk@4ax.com:

On Sat, 19 May 2012 08:51:38 -0400, "Bill Proms" <none@anywhere.us
wrote:

I have 3 Intelli-Time LED alarm clocks around the house, just like the
one here:

http://www.acurite.com/clock/alarm-clock/intelli-time-digital-alarm-clo
ck-13027a2.html

I initially bought these due to them keeping time when the power goes
off and auto resetting for DST. There is a problem, however. Each of
the clocks becomes inaccurate over time. If I set them all manually
to the same time, within a few months, each one will be off by 3-5
minutes.

So I ask, what is the problem and is there any way to repair it?

Several problems and combination of problems.
1. Noise on the power lines triggering added pulses. This will make
the clock run fast.
2. Internal free running oscillator is off frequency.
3. Crappy design.

I once modified a vacuum fluorescent alarm clock to keep accurate
time. I opened the device, figured out what chip was used, looked at
the data sheet, and replaced the crappy RC oscillator with a 32KHz
clock crystal. When the AC power disappears, the display goes blank
and the internal 9v battery runs the clock. The problem is that the
battery drain was so high that it would kill the 9V battery in about 6
hrs. There was also no charging circuit. So, I replaced the 9V
battery with 4ea AA NiCd batteries (the clock chip would still run on
about 6VDC), and added a crude trickle charger.

was that a 32KHz crystal,or a 32KHz ceramic resonator?
I suspect it's the latter.that would explain the poor freq.stability.
You can trim up an XTAL oscillator.

ALmost certainly a crystal; ceramic resonators have way too much drift
with temperature. 32 KHz crystals are very difficult to trim because
they don't like to have any extraneous capacitance hung on them.

Isaac

 

[isw]

In article <h9dfr71u6fchkgccmmpjd31m95ifn47s6k@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

On Sat, 19 May 2012 07:53:46 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net> wrote:

I once modified a vacuum fluorescent alarm clock to keep accurate
time. I opened the device, figured out what chip was used, looked at
the data sheet, and replaced the crappy RC oscillator with a 32KHz
clock crystal. When the AC power disappears, the display goes blank
and the internal 9v battery runs the clock. The problem is that the
battery drain was so high that it would kill the 9V battery in about 6
hrs. There was also no charging circuit. So, I replaced the 9V
battery with 4ea AA NiCd batteries (the clock chip would still run on
about 6VDC), and added a crude trickle charger.

The world's first clock-radio with an all-electronic digital clock -- a GE,
which I still have, 40 years after I bought it (!!!) -- used a nicad-powered
oscillator running at ~ 60Hz to keep the timer going. I don't think it ran
more than about 10 minutes.

I think I remember seeing those. Todays version will last about a
year before something blows or it falls apart. Progress?

Way back in college daze (1960's), one of my friends was trying to
devise a method of running a motor drive electric clock during power
outages. I designed a line sync blocking oscillator, that ran in sync
with the 60Hz power line frequency when that was present, but ran off
battery power at roughly 60Hz when that disappeared. To get
sufficient power to run the clock, it had two 2N3055 transistors
playing push-pull oscillator to a small power transformer. It was
big, noisy, and ugly, but worked quite well. Keeping the wet cell
battery charged was the major challenge. We were thinking of
manufacturing these, but was talked out of the idea by someone with
more marketing sense than us.

The analog wall clocks in high skool were all wired to central time
controller. Curious as to how it worked, I dragged an oscilloscope
into the main hallway to clip onto the only accessible wires I could
find. Every 15 minutes, a sync pulse would appear on the line,
resetting the clocks to the nearest 15 minutes. Every hour, two
pulses would reset the clocks to the nearest hour. At noon and
midnight, 5 pulses would reset the clocks to midnight. Unfortunately,
gathering this intelligence required almost constant monitoring, which
attract too much attention. I was caught before I could make the
clocks run backwards. Not a great start for my first attempt at
hacking.

When I was in college, (mumble) years ago, I built a 4-channel SCR light
dimmer for the theater department. To my delight, the noise it put on
the power lines would not only set the clocks, but also ring the bells.
It was fun disrupting bridge games in the student union.

Isaac

 

[isw]

In article <gkqfr7tifijlt1n4l7frdrb5pumccv7tad@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

On Sat, 19 May 2012 18:24:04 +0000 (UTC), "Geoffrey S. Mendelson"
gsm@mendelson.com> wrote:

It's because the US is trying to get rid of those broadcasts. With GPS they
are obsolete.

I beg to differ. The cost of a GPS disciplined oscillator or clock in
a consumer product is prohibitive. Running continuously, GPS is a
major power drain. GPS doesn't work well indoors. There are huge
number of products that currently use 60KHz time sync that will go
dark if the US pulls the plug on WWVH and WWVB. That's not going to
happen. Quite the contrary, there are plans to add a US east coast
transmitter. See:
http://en.wikipedia.org/wiki/WWVB
under "Service Improvement Plans".

Incidentally, I'm building my own 10MHz GPSDO for running my test
eqipment and ham junk. It's NOT a trivial or inexpensive exercise:
http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm

You can get short-term performance equal to a good crystal and long-term
accuracy pert' near equal to the cesium beam clocks on the satellites
for a whole lot less than that.

Start with a 10 MHz rock in a home-brew oven, and divide it down to make
a "regular clock". Compare the time given by that clock to GPS time, and
twiddle the crystal oscillator to make it track, using a very long time
constant filter in the loop. The longer it runs, the more accurate it
gets.

After it's run for a while, you can do without GPS updates for fairly
long periods (depending on how good your oscillator/oven is) with very
little loss in accuracy.

I've considered building that sort of rig where the oscillator's
frequency is controlled by altering the temperature of the oven. The big
advantage of doing things that way is that there are no extra paths for
noise to get into the oscillator, as there would be if you used some
sort of variable capacitor.

Isaac

 

[isw]

In article <501gr7tu7t78vukr1a1fnjsirfqc00dvfg@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

On Sat, 19 May 2012 21:20:26 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:

Incidentally, I'm building my own 10MHz GPSDO for running my test
eqipment and ham junk. It's NOT a trivial or inexpensive exercise:

A while back (I think it was) EPE magazine (or might have been Elektor)
published a GPS frequency standard generator projects.

There are plans all over the internet. Almost all of them use the
Rockwell Jupiter board, which has a convenient 10KHz output. That
would normal be the way to go, except that I have a large pile of
Novatel Allstar 12 boards, which have 1Hz and 10Hz outputs. That
makes the design somewhat more complicated.

Its available as a kit, so although not particularly cheap it is fairly
easy.

Complete GPSDO modules can be found for about $300.
http://www.navsync.com/GPS_timing.html
http://www.navsync.com/docs/CW46_prod_brief.pdf
I'm building mine much the same way, with integrated antenna, etc.

The 1pps output can be used to run a digital clock, but I would hate
to see the final cost.

Why use the 1 pps? Any cheap GPS you get on eBay will output NMEA
"sentences" in ASCII that tell you the precise time. Just use those.

Say, $15 for the GPS, another $15 for an Arduino, $5 for an LCD, and
whatever crystal you have on hand, stuck in a home-made oven. Maybe
another $20 for all the "glue", and the rest, as they say, is just
software.

Isaac