WWV Radio-Controlled Clock


This is a digital clock I designed and built, initially over 20 years ago. In 2001, I upgraded the original design to use a PIC chip for decoding and time keeping and I redesigned the the receiver for better performance. This clock automatically synchronizes itself to the National Institute of Standards and Technology (NIST) atomic clock and displays the precise time of day. The NIST broadcasts time of day and other information on 5, 10, 15, and 20 MHz. These shortwave stations also broadcast a time code on a 100 Hz subcarrier using a modified IRIG-B format. My clock has a crystal-controlled radio that receives WWV on 5, 10, and 15 MHz. The radio will scan for the strongest signal. The clock has a Microchip PIC that decodes the 100 Hz time code to set its internal clock to the correct time. A DIP switch tells the PIC which time zone to use since WWV sends time in Universal Coordinated Time (UTC). The clock also adds 1 hour for Daylight Saving Time (DST) and illuminates a LED when DST is active. Pushing a button on the lower right of the clock will display the day of the year as sent out by WWV. A switch to the right of the display sets the display to display either local time or UTC. The meter in the center of the front panel displays received signal strength. Three LEDs below the display indicate status of the time setting. There is one LED each for seconds, minutes and hours. When the clock has updated seconds, minutes, or hours, the appropriate LED extinguishes. WWV sends out the time via the modified IRIG-B format in series. Seconds is synchronized with the 1000 Hz tone at the beginning of the minute. When that tone is received, the clock will set the seconds to zero. Next the minutes is transmitted, followed by hours, followed by day of the year, and finally DST. Thus the LEDs extinguish in a sequence.

The internal radio does not remain on all of the time. Once the time has been set, the radio turns off and turns on again 1.5 hours later. Thus the time is updated approximately every 1.5 hours. If the signal strength is not sufficient, the clock will not set but maintain the time it determines using its internal crystal-controlled oscillator.

Below is a picture of the CPU board and the inside top of the clock. Yes, I know it is messy, but it works. The mass of wires on the right is associated with the display. The display was not redesigned.



Below is a picture of the receiver board located on the underside of the clock.



The original version of this clock comprised over 40 CMOS integrated circuits and a single conversion radio receiver. Incorporation of the PIC allowed me to add the day of the year feature and better error correction techniques. I designed and added a dual conversion receiver to improve sensitivity and selectivity. Below is a picture of the original digital electronics. This board was all point-to-point wiring.



Below is a picture of the original receiver. I retained the original point-to-point wired frequency select board (it uses blue perf board as seen in the picture of underside of the clock shown earlier). However, some of the original circuitry was incorported in the new digital board and therefore some ICs were removed.



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