7400 competition entry: Discrete logic POV clock

Matt’s entry in the Open 7400 Logic competition: Discrete logic POV clock.

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.

Via the contact form

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