How do auto-set clocks grab the time?

I believe that they have battery-backup real time clock chips just like you would find in a pc.

Bob

I don't know but my VCR gets its time from a TV channel. There's also something called WWV.

My cordless phone got its time from caller ID. Now if only they could all agree...

approx.

the

time

GPS receiver?

Maybe RDS / RBDS. It only requires an FM receiver, and some logic to scan the band for a suitable station.

"BobW" wrote in news:OtednWXI3dUit-LanZ2dnUVZ snipped-for-privacy@giganews.com:

That much seems clear, but I'd like to know how the time stays current, e.g. what signal keeps it from getting steadily off track? I assume it must come from either the "air" or the 60hz AC line. I ruled out "air" because no mention is made of a receiver or FCC rules.

I own 2 "Atomic" (Colorado radio signal) clocks, which update almost nightly and are very accurate.

It looks to me like "auto-set" clocks are less (pinpoint) accurate than manually setting a normal clock once a month or so. The convenience of instant reset after an outage seems like the main appeal.

Unless it's pure marketing, they must be different than a regular clock with a 9V battery backup, but how exactly?

Jack

I know that PBS stations broadcast time signals, and I assume NPR stations do the same.

They probably use a sub carrier and some FSK to burst out the time info.

"Richard Henry" wrote in news:AEJfj.25807$ snipped-for-privacy@newsfe16.phx:

There's no mention of any receiver, and $15 for a GPS circuit would be a steal. The exact model is a Sony ICF-C318. The manual says the time was preset (EST) at the factory and makes vague references to temporary inaccuracy. You have to verify or change your time zone at first run.

One buzzword I found is ATS (Automatic Time Set), which does use a radio signal, but so far I only see that mentioned for the UK.

Jack

innews:AEJfj.25807$ snipped-for-privacy@newsfe16.phx:

The WWV signal is shortwave, maybe your clock uses the house wiring as the antenna. I haven't stuck a scope in the wall outlet ever, there might be all kinds of fun stuff on there.

innews:AEJfj.25807$ snipped-for-privacy@newsfe16.phx:

It more likely uses WWVB, with is a 60KHz signal, available most everywhere in the continental USA.

See...

for a WWVB receiver I designed in 1973-74.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

WWVB is a special NIST time signal radio station near Fort Collins, Colorado, co-located with WWV. WWVB is the station that radio-controlled clocks throughout North America use to synchronize themselves. The signal transmitted from WWVB is a continuous 60 kHz carrier wave, derived from a set of atomic clocks located at the transmitter site.

Since WWVB's low frequency signal tends to propagate better along the ground, it requires a shorter and less turbulent path to get to the radio receivers than WWV's shortwave signal, which is strongest when it bounces between the ionosphere and the ground. This results in the WWVB signal having greater accuracy than the WWV signal as received at the same site.

The auto set clocks I have seen, use a loopstick antenna.

donald

innews:AEJfj.25807$ snipped-for-privacy@newsfe16.phx:

I have an inexpensive Casio 'atomic' watch that reads WWVB automatically, periodically when it can, and corrects the time. A bit bulky.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I see, thanks. Makes me want to buy one of these clocks and cracking it open.

innews:AEJfj.25807$ snipped-for-privacy@newsfe16.phx:

Probably uses a loop antenna ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

There are at least three possibilities:

1 - When the 60Hz power is available, it keeps the RTC updated (since the 60Hz is MUCH more accurate than any 32KHz crystal), and then when the ac power goes away it reverts to the 32KHz crystal.

b - The RTC is always updated by its 32KHz crystal.

3 - the clock runs off 60Hz (when available) and the RTC when no ac is present.

If it were mine, I would take the dang thing apart and figure out how it worked. Then, I would go buy another one because I can NEVER get anything I take apart back together again.

I looked at these a while ago, and decided that the WWVB clocks were much better -- although they're more temperamental.

Bob

Seems like they're using television signal.

fe16.phx:

The manual suggests that it contains a lithium CR-2032 button cell to power the factory set CMOS timer IC when the unit is not plugged into the national grid. Their publicity blurb says it is a radio settable clock (which in the UK would certainly be possible off the FM channel RDS info). However, it also includes instructions for manually setting the time and talks abut coming up 00:00 if the backup battery fails which tends to suggest that it isn't a truly self setting automatic radio clock.

My CH clock includes a similar backup clock circuit (they are as old as the hills) to avoid having to reset it after a power failure (unlike the oven and microwave which do not).

A lot of UK clocks (and European ones) use either Rugby MSF 60Hkz or the German DCF-77 to automatically set themselves. Ad men usually adevrtise them as atomic clocks. Some modern FM radios can do it too via RDS, although I have an early model Hitachi AX-M68D that can decode the signals and in use displays time date OK, but fails to update its standby clock. It clearly has one but the model I have seems to lack the right firmware - it displays the time as " _ _ : _ _ " in standby. Later models work OK. There may be a hidden keychord to force set time mode but I have yet to find it (anybody know of one for this model ?).

NB. DAB based time signals can be up to 1-2s out of sync with reality. There was no standardisation of the decode time and so it even varies with chipset. Listening to the UK pips on FM and DAB simultaneously is amusing. Only astronomers and the military tend to get upset about a few seconds error in reference time signals though.

Regards, Martin Brown