LED alarm clocks all lose accuracy over time

[Cydrome Leader]

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.

I think it was GE that had an alarm clock like that in the late 70s. It
was actually pretty cool. It had a little keypad on it.

 

[Geoffrey S. Mendelson]

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".

That's dead. What's left as of March 2012 is a plan to move from AM to BPSK,
which is supposed to make it possible to receive the signal farther away
and in areas with more noise and multipath distortion.

There was a trial in early March, any see any results yet?

How will this affect any old devices that use the AM signal method?

Will someone be selling, as I proposed (and shouldda patented) devices that
get the correct time via NTP and broadcast microwatt signals for local area
time sync?

Geoff.

 

[William Sommerwerck]

I think it was GE that had an alarm clock like that

in the late 70s. It was actually pretty cool. It had a
little keypad on it.

I mentioned that in a preceding post. It was the 7-4760, I believe. I still
have it. The keypad needed cleaning every couple of years.

 

[Smarty]

Not quite correct.

AFAIK, Heath made the world's first digitally tuned stereo FM tuner. The kit
was appallingly expensive -- around $550 35+ years ago. It used little cards
you notched for a particular station. I saw it at a hi-fi show, with the
Heath rep explaining how you could use it to monitor the station's broadcast
frequency. (In my best Menckenesque manner, I set him straight.)

Tuners with direct frequency entry were and are uncommon, because it
requires a keypad, plus a decoder to output the digital value needed to set
the local oscillator. As the tuner would have a station memory anyway, which
most people would use to store their favorite stations, direct entry has
little advantage (except during initial setup).

GE made at least two clock radios with direct entry. (Yes, I have one.)
Because there's no overlap between AM and FM frequencies (in kHz and MHz),
you didn't need to specify the band.

Component tuners with direct entry are virtually unheard-of. Toshiba had
one, I believe, and my Parasound T3 permits direct entry from the remote
control.

Does anyone know of any others?

Dick Sequerra made one as I recall, and the RACAL, Rhode and Schwartz,
and other surveillance receiver makers also had direct synthesis /
tuning as well.

 

[Cydrome Leader]

I mentioned that in a preceding post. It was the 7-4760, I believe. I still
have it. The keypad needed cleaning every couple of years.

I once had the older vacuum flourescent version. They changed to LEDs at
one some point. I forgot how/why mine broke.

 

[Geoffrey S. Mendelson]

If you're building a clock, the noise and jitter aren't very important;
long-term drift is.

It's also part of the modern perception that precision is much greater than
it is. A clock that reads hours and minutes is accurate to around 30 seconds.
A clock that reads hours minutes and seconds is accurate to 1/2 second.

Neither are accurate to a millisecond.

I it started with airlines who would write 12:30 for "sometime before 1
o'clock" for departure and 2:00 for "around 1:30" for arrival. People
expect exact numbers where they are approximate, and it is easy to
arrive on time if you allow enough "slop" to commenpensate for anything.

Mousillini (pardon the spelling) "made the trains run on time" by adjusting
the schedules to reality.

I've also seen it in ham radio where the frequency really is around 14.200,
but someone logs it as 14.203154 because that's what their (inacurate)
receiver reads it as and in computers where someone thinks floating
point numbers are integers. :-(

For most people a clock that reads in minutes is ok, and for almost everyone
who needs more accuracy seconds is ok. Just about every clock made stays
within a second for a few minutes, and auto correcting via GPS, NTP or WWV
would do well enough.

I would expect that an HF receiver clock where you set the minutes and it
autocorrects to the minute pips on WWV or CHU would do fairly well, and
in most of the US and Canada do it without the interference problems
the VLF radios have.

Note that I don't have access to any of those sources, or the EU equivalents.
The best that I can do is to run real NTP clients on all my computers,
which sync to a main NTP server on my network.

The main NTP server syncs to a variety of sources, which confuses it because
they are all within a millisecond of each other except for two Apple EU ones
which are 5 seconds off. I put them in a long time ago and probably should
remove them.

The irony of all of this is the only thing that needs accurate timing is
catching a bus, which never comes at any exact time anyway and recording
programs off of the DBS system I susbscibe to.

Since we have their PVR, it gets its time and programing information
from the feed, but is set to start recording early and end late.
They don't even trust themselves.

Geoff

 

[JW]

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>

Too expensive.
Get this while it lasts for $135:
http://www.ebay.com/itm/TRIMBLE-GPS...315?pt=LH_DefaultDomain_0&hash=item27c728a56b

I almost went for one of those, but instead decided on this:
http://www.ebay.com/itm/28065523326.../sch/i.html?_sacat=0&_nkw=280655233263&_rdc=1

Not quite as accurate as the thunderbolt, but good enough for my bench.

 

[William Sommerwerck]

I once had the older vacuum flourescent version. They
changed to LEDs at one some point. I forgot how/why
mine broke.

The vacuum-fluorescent version did 'not have a digital tuner. (I have that
one, too. It works, but it could stand a bit of fixing-up.)

 

[William Sommerwerck]

It's also part of the modern perception that precision

is much greater than it is. A clock that reads hours
and minutes is accurate to around 30 seconds. A
clock that reads hours minutes and seconds is
accurate to 1/2 second.

You're confusing accuracy and resolution. You're also ignoring the fact that
the user can //see// when the minutes change. If you make sure the minutes
change at the same time your reference clock changes, the clock's accuracy
can be less than one second.

I've also seen it in ham radio where the frequency really
is around 14.200, but someone logs it as 14.203154
because that's what their (inacurate) receiver reads it as
and in computers where someone thinks floating
point numbers are integers. :-(

I don't think most digital communications receivers display the frequency
with a precision the LO is capable of.

 

[William Sommerwerck]

I've also seen it in ham radio where the frequency

I don't think most digital communications receivers
display the frequency with a precision the LO is
capable of.

WHOOPS! That should have been "incapable of".

 

[Geoffrey S. Mendelson]

WHOOPS! That should have been "incapable of".

Well, my 1980's Kenwood TS-430 is capable of tuning in 10Hz steps, and
the modern high priced rigs in 1Hz steps.

Geof.

 

[William Sommerwerck]

My 1980's Kenwood TS-430 is capable of tuning in 10Hz

steps, and the modern high-priced rigs in 1Hz steps.

I'd like to make a joke about "high-priced [band]spread", but I will
refrain.

The former resolution would require the synthesizer's crystal to be accurate
to about 1 part in 100,000, which is not out of the question.

My Yaesu FTD-1000 is in storage. I don't remember its resolution, or the
tolerance of its crystals.

 

[jeff_wisnia]

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....)

I wish the most recent MW oven I bought for our office worked like that.
Its clock gains about one minute a day and I doubt that there's any
syncing to the line frequency built in. It keeps far worse time than the
$10 battery powered wall clocks we use around the office.

Could be the problem is that the temperature of the electronics in that
MW oven moves around quite a bit more than those in the clock on the
wall next to it due to the high power loads when the oven is heating
stuff. That could screw up a simple RC or even xtal oscillator, eh?

OTOH the MW oven in our home's kitchen is always dead nuts on time,
barring power failures, after which it needs resetting.

Jeff

Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.

(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.)

--

 

[Geoffrey S. Mendelson]

I wish the most recent MW oven I bought for our office worked like that.
Its clock gains about one minute a day and I doubt that there's any
syncing to the line frequency built in. It keeps far worse time than the
$10 battery powered wall clocks we use around the office.

More likely it has one of those chips that detects if there is power line
signal or battery backup and uses a built in crystal to keep time if the
power line goes off.

Unfortunately, at least one of the cheap Chinese versions is broken and uses
the crystal all of the time. I have a clock like that.

The crystals are spec'ed to run a microprocessor in the chip and not keep
time. :-(

Geoff.

 

[Spehro Pefhany]

I think it was GE that had an alarm clock like that in the late 70s. It
was actually pretty cool. It had a little keypad on it.

I had one of those- nice. IIRC, the keys failed over time though.


Best regards,
Spehro Pefhany

 

[Geoffrey S. Mendelson]

Then why did they replace the WWVB towers & transmitters a couple
years ago? They built a better antenna array, and raised the
transmitter power so that it can be received in Florida on a $20 'Atomic
clock'.

They are playing "cheap catch up". The original plans were to build an
east coast station, but they were unable to get any government installation
to "host" it, (NIMBY) and lost the funding.

Not only are they not looking to discontinue the service, but they
are looking at a new modulation method to improve noise immunity. This
web page from NIST says that there are about 50,000,000 radio controlled
clocks using WWVB in the United States:

The are using the improved modulation to keep relevant. In most large cities,
the noise from computer and home electronic equipment, BPL (still very much
in use but not for internet to customers), aDSL, etc has made it next
to impossible to receive a signal.

They exist today because people are willing to accept the poor service they
get as it is the only game in town at that price tag. Most users never
pay attention to how often they get sync, if ever.

If they have to pay $100-$150 for a BPSK decoding clock, GPS or Wifi NTP clocks
will seem a lot better deal.

I'd love to know how they came up with the number of clocks in use. Anyone
have an idea?

Geoff.

 

[Geoffrey S. Mendelson]

Many switching power supplies run at about 60KHz. I have one
somewhere around my computer/TV pile, which kills WWVB reception if I
get anywhere near it.

Exactly, how many people have one?

Most WWVB devices have an indicator on the LCD display to show that
the clock was recently synced with WWVB time. My weather stations and
assorted digital clocks all have this feature.

What's recent? 1 minute? 1 Hour? 1 Day? a Week?

It's my understanding that only the modulation scheme will change, not
the encoded data. A universal chip that works using both system
should be possible without a major price jump.

Well no. The data is the same, but a new receiver needs to be used.
The old one just did on/off for an AM pulse, the new one uses BPSK,
which is two tone modulation. So not only does it have to decode
the carrier being there at all, it has to decode two different tones.

Then you have to decode the BPSK stream to get the data. This not a big
deal, you could do it with a sound card and a microprocessor, but it's
a different receiver design, and reprograming the microprocessor.

The kind of thing that if you really were going to sell 50 million of them
you could do it for a few dollars a chipset/board, which is probably what the
current ones cost, but if you want to break even with 10,000 you have to
sell them for at least $100, maybe more.

It's like I saw an article about an Israeli startup that had sold 200,000 of
their product. The article was entitled "sales of xxx disappointing".
I guess they planned on selling a million of them. :-(

I'm a bit mystified with the "new type of PM receiving antenna"
mentioned in:
<http://www.nist.gov/pml/newsletter/radio.cfm>
I didn't know that antennas were modulation specific.

Where have you been the last five years? I surprised that you have not
been swamped with HDTV antennas.

I expect it's another gimick to say you need to buy a higher gain antenna,
or that's why your device can't sync. I expect that everyone will need
to buy 1/2 wavelength end fed wires.

(for the humor impared, that's a joke, a wavelength is 5 kilometers).


Geoff.

 

[josephkk]

Well no. The data is the same, but a new receiver needs to be used.
The old one just did on/off for an AM pulse, the new one uses BPSK,
which is two tone modulation. So not only does it have to decode
the carrier being there at all, it has to decode two different tones.

Ummm. No. BPSK is a variant of Manchester encoding.

Binary Phase Shift Keying. Single frequency.

 

[Carolee]

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

Thanks in advance,
Bill

Maybe you should switch to sundials, you fucking peckerhead.