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Problem with 4017 counter

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e_neophyte

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I'm REALLY new at this so go easy! I've just breadboarded a simple circuit that uses a 555 timer to clock a 4017 counter and light a series of 10 leds in sequence. (I'm just doing this to learn how these circuits work.)

The circuit works fine except for one thing: When I turn the power on, output 2 (pin 2) lights up first followed by outputs 3, 4, 5, 6, 7, 8, 9, 10. The second sequence then starts properly with output 1 (pin 3) followed by outputs 2, 3, 4, 5, 6, 7, 8, 9, and 10.

In other words, output 1 is skipped the first cycle but each subsequent cycle works correctly.

Why does this happen? My input pins are each grounded (no floating inputs). The correct leds are connected to the correct pins (according to two different pinout sheets that I've consulted). What am I doing wrong?

As an aside, if I hook up output 1 AS THOUGH IT WERE OUTPUT 10, the leds fire in the desired order but ACCORDING TO THE PINOUT, they are firing as 2, 3, 4, 5, 6, 7, 8, 9, 10, 1.

Any help appreciated!
 

Brevor

Member
4017

You need to apply a short pulse to the reset pin at power up. This sets the counter to zero. You can do this with a .1 uf cap and a 10K resistor and a diode connected as a differentiator network to the reset pin (15).
Put the cap between pins 15 and 16 the resistor goes from pin 15 to ground,
put the diode in parallel with the resistor with the cathode (banded end) to
pin 15.
Or it may be less work to just re-label your led's.
 
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e_neophyte

New Member
Thanks for your reply Brevor. Is it normal to have to charge the reset pin of the 4017 at the beginning for it to start outputting at output 1 (pin 3)? I'm not making this circuit for any purpose other than to learn with. I'm just trying to figure out why it doesn't work the way the instructions say it should work. (I'm using the Electronics Projects for Dummies book).
 
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