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I am making a simple circuit. It has 5 x 74ls161 4-bit counters, and 4 logical ICs (2 x and, not, or). Regardless the logic of my circuit. After I added the last IC (bottom, 74ls32 quad and), the 2nd 4-bit counter stopped working. After 10 seconds, it worked again, then stopped after a minute. It happened before with the other leftmost 74ls161 counters. Sometimes they just stop working, or the increase count by 2 (lsb is always 0.)

I added these 47μF to each IC, but it didn't make a difference.

I am missing something here and I don't know why.

More importantly, how do I check that this won't happen again?

Thank you!!

my breadboard

Gil Megidish
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  • Check that your power supply has a high enough maximum output current. – user25093 Jul 20 '13 at 10:00
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    [What is a decoupling capacitor and how do I know if I need one?](http://electronics.stackexchange.com/questions/2272/what-is-a-decoupling-capacitor-and-how-do-i-know-if-i-need-one) – Phil Frost Jul 20 '13 at 12:05

1 Answers1

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Add a 100nF capacitor across power supply pins of every single IC and a big 47uF or 100uF capacitor once on the power rails of the breadboard. Keep the connections between IC and 100nF cap as short as possible.

The 100nF decoupling caps are much better than electrolytics (like your 47uF) at suppressing fast transients caused by the logic inside the IC's switching.

jippie
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  • Thanks for the answer! How would have I found that myself? any tools? datasheets? – Gil Megidish Jul 20 '13 at 09:57
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    Intersil application note 1325. Analog Devices application note 1099. Murata application note DCAN-58. Cypress application note 1032. Texas Instruments application note SCBA007A. And dozens more. – Ignacio Vazquez-Abrams Jul 20 '13 at 10:12