Digital Clock

24 Hr Digital Clock only with basic CMOS Chips

This is a 24 hour clock based on dual decade counters, AND gates, OR gates, BCD to Decimal Converters, and a 555 timer clock source. No micro controllers are used in this project.

Parts List

(6) 74HC390 Dual Decade Counters

(6) 4543 BCD to seven segment decoder ICs

(1) 74HC08 Quad AND Gate

(39) 500Ω or 1000Ω drop down resistors for 7 segment displays

(3) 10kΩ Resistors

(6) Common Anode 7-Segment Displays

(1) 100 uF Capacitor

(1) 555 timer ic

(3) Momentary Switches

(1) 3 mm Red LED

Block Diagram

WORKING

555 generates a 1 Hz clock signal which is fed into the first dual decade counter [IC3] which runs from 0-9. The binary coded decimal from IC3 is fed into a BCD to seven segment decoder IC  4543 [IC4] which drives the seven segment display. The drop down resistors, 500Ω for a bright display or 1000Ω for a dimmer display are used in series with the seven segments but not shown in the diagram.

IC3 triggers IC5 by feeding its IC3's q3 output into IC5's clock input. IC5 runs from 0-5 and resets via an AND gate when it hits 6. The AND gate also feeds into IC7 which is the minutes section. IC9 resets at 6 as well. This completes the minutes section.

The AND gate from the minute section increments the hour section. Another AND gate in the hours section resets IC11 and IC13 simultaneously when  they collectively reach 24.

Video of Final Working Product