This persistence-of-vision clock was built entirely out of discrete logic chips. The design consists of three boards, a LED array and a drive motor. The digit board keeps the time while the display board controls the LEDs.
The digit board
Every second, a pulse increments the value stored in a counter. When it overflows, the next counter is incremented. Each counter represents a digit in the time. A decoder selects one digit at a time and puts that digit’s value on the output bus.
The display board
A pulse from an external source wakes up the display board. It selects the leftmost digit from the digit board, formats it for a 7-segment-display, and chops up the result into a 5 x 5 pixel matrix. It lights up LEDs for each column in sequence then selects the next digit to the right.
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