Electronic – 60 LED chaser sequencer, two LEDs turn on at a time instead of one

cd4017

I am trying to make a 60 LED chaser. I don't want to use microcontrollers as it makes the job too easy. I have got lots of CD4017s with me. I searched the internet and got a comparatively simple circuit which I am attaching herewith. Instead of 60, I tried out a modified 20 LED version in a breadboard. Now I shall explain my problem. As per the circuit, the LEDs should turn on one at a time. But physically, Q0 of IC3 turns on first. Then Q0 of IC4 turns on (IC3 Q0 is still on). Then IC3 Q0 turns off and IC3 Q1 turns on (IC4 Q0 is still on). That way it's always 2 LEDs n at a time instead of 1. Any idea why? Any inputs deeply appreciated.

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Best Answer

The 4017 is a decoded decade counter which means that one of its outputs is always on. So at reset Q0 is active this will apply to both IC3 and IC4. When you clock IC3 it changes the active output from Q0 to Q1.

If you are trying to achieve a single light that runs from one end of a display to the other you would probably be better off building a shift register to do that using something like several 74HC595s.

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