What time is it? Is a common phrase, but at one time the answer was a bit more ambiguous than the super accurate timing that we have access to through NTP, GPS, and various RF-broadcast atomic clock signals. Once such signal is known as DCF77, and emanates from Mainflingen, Germany.
While most would just use such a signal and go about their slightly-more-accurate day, hacker Brett Oliver designed a clock that displays info about the signal itself. Not only does it reveal the decoded time and date using 7-segment characters, but also the actual binary data received in a series of two concentric 60-LED rings on the outside of the face. Further info is shown by a number of status LEDs.
The CDF77 clock works using a pair of ATmega328P-PU microcontrollers laid out in a veroboard setup. These control LEDs with the help of three MAX7219 LED driver modules, and play sounds through two JQ6500 sound modules. An RTC module is included in the design as well, along with of course, a DCF77 receiver. A Superfilter routine running on one of the MCUs is available to help keep accurate time, even with a noisy signal. Clock settings can be changed via a series of switches that swing down from the bottom of the clock.
Two different physical clock configurations have been implemented so far, a classic round face and another with a more modern square look. For another take on the design, you can find info on the first version here.