A digital clock keeps track of time and displays time in three numeric values - hour, minute and second. Each value is displayed using two decimal digits. The minute count and the second count display integral values ranging from 00 to 59. In the 24-hour mode, the hour count displays integral values ranging from 00 to 23; in the 12-hour mode, the hour count displays integral values ranging from 01 to 12 and the clock would show whether in the AM or in the PM using an additional indicator. The second count increments its value by 1 at the rate of 1 Hz. When the second count overflows, the minute count is incremented by 1; when the minute count overflows, the hour count is incremented by 1. This is a link to an online digital clock.

In addition to running the time and displaying normally, a digital clock also need a setting mode, in which the minute value and the hour value can be adjusted manually.

Our digital clock implements all of the above functionalities. It displays the three numeric values on six 7-segment LEDs on the printed circuit board (PCB). It keeps track of the current time and computes the display outputs in the integrated circuit (IC).

The figure above shows the core part of the project. It uses off-chip crystal to provide a stable clock resonance and inside the IC is where all the digital logic computations take place (boxed by dotted lines). We added extra circuitries for reliability, but the diagram above shows the essential components in the entire project.