Introduction

Building a clock from TTL (Transistor to Transistor Logic) chips is a challenging but rewarding project. It requires careful planning, precise wiring, and a deep understanding of digital logic. On this page, I'll be sharing my journey as I design and construct this classic piece of electronics. Expect to see schematics, breadboard layouts, and maybe even a few troubleshooting tips as I work through the inevitable bugs. This project is a great example of the engineering design process in action, and I hope it inspires you to tackle your own hardware challenges. 

Parts List (Bill of Materials)

How it Works

This clock uses a combination of integrated circuits (ICs) to keep time and display it. It all starts with a 555 timer, which acts like a tiny heartbeat, generating a precise electrical pulse every second. This pulse drives a shift register with 30 LEDs. Each pulse lights up one LED, creating a visual representation of the seconds ticking by. After 30 seconds, all the LEDs are lit, and the shift register empties, turning off LEDs one by one for the next 30-second cycle.

These second pulses also feed into counters. A 7490 decade counter counts the minutes up to 10, and then triggers a 7493 4-bit binary counter to increment the 10s of minutes. Similarly, the minutes counter triggers another 7490 and 7493 to increment the hours. These counters store the time in binary coded decimals (BCD).

To display the time on the 7-segment displays, we use 7447 decoder ICs.

These decoders translate the binary code from the counters into the signals needed to light up the correct segments of the display for each digit.  So, the large 7-segment displays show us the time in a way we can easily read.

Block Diagram

The Clock and Shift Register