Digital Atomic Clock
Tune in WWVB on 60 KHz,
decode the time pulses,
and always have the True Time.
Never be late for work again. You can be in the office within a couple
milliseconds of the opening bell.
It's difficult to photograph light sources, so please bear with me as we go
through the pics.
The display is made up of 1-inch high, 7-segment modules. I used red for the
hours and minutes and green for the seconds. That combination seems to
make "reading at a glance" very natural.
The microprocessor "looks" for WWVB signals, in Fort Collins, Colorado,
beginning at Midnight. During the "seek" time, the displays are blanked to
reduce digital noise. Pushing the Reset button brings the digits back to life.
The onboard frequency standard maintains extremely accurate time between
Although there is an external antenna port, the two onboard ferrite loops do a
good job of receiving the slow pulses. Regardless of which of the three
antennas are used, the input signal needs to be filtered through a bandpass
filter, otherwise any random noise pulse or hash will disrupt the slow digital
chain and invalidate the data string.
The display brightness can be set from too
bright to too dim. Even though I have the setting
at about 20% in this photo, it's still too bright for
an automatic shutter - the room is actually well
lit in this picture.
This circuit also incorporates an alarm setting
(Event Trigger) and is of the type that
automated radio stations use to cue-in
syndicated programs, commercials, and any
other material that needs to maintain seamless
programming continuity. The events can be
controlled from a "Form-C" relay which provides
normally open or normally closed contacts.
Details of the semi-completed assembly.
The front panel is the only metal in the clock's
construction -- the case and cover are ABS plastic
to allow the sync signals to be received by the
When mounted in an equipment rack, if the rack has
a back door, it must be left open and facing West ...
otherwise the external antenna port must be used,
along with a suitable antenna. I use an available
80-meter dipole or a 160-meter Marconi.
Status and Power control
Calibrating the 8-inch ferrite loopstick to resonate at 60 KHz.
More to come as I finish this thing...
WWVB is a 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. A one-bit-per-second
time code, which is based on the IRIG "H" format of time code and derived from the same set of atomic clocks, is then modulated onto the carrier wave using a technique described as
pulse width modulation followed by amplitude-shift keying. A single complete frame of time code begins on the second, lasts one minute, and conveys the year, day of year, hour, minute,
and other information as of the beginning of the frame.
While most time signals encode the local time of the broadcasting nation, the United States spans multiple time zones, so WWVB broadcasts the time in UTC, which the radio-controlled
clocks then have to convert to their own local time.