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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Weird 4017 behaviour
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CHRISKELLY



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PostPosted: Tue Oct 16, 2018 1:09 am    Post subject: Weird 4017 behaviour Reply with quote  Mark this post and the followings unread

I'd set up a simple 8 step sequencer using a 4017 on breadboard which worked as expected.

Just transferred to perf and it's behaving differently:

Each step is only gating on the first half of the clock cycle so instead of a seamless stream of notes, I get half notes Shocked

Clock enable tied to ground and it resets correctly.

Any ideas what is happening here??
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Steveg



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PostPosted: Tue Oct 16, 2018 5:38 am    Post subject: Reply with quote  Mark this post and the followings unread

??? Circuit?
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CHRISKELLY



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PostPosted: Tue Oct 16, 2018 7:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Very crude sketch Very Happy


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PHOBoS



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PostPosted: Tue Oct 16, 2018 8:31 am    Post subject: Reply with quote  Mark this post and the followings unread

What signal are you trying to switch with the 4066 ? The 4017 can't turn ouputs off for half a clock cycle
which you should be able to check, maybe with some LEDs.

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CHRISKELLY



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PostPosted: Tue Oct 16, 2018 9:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeh the first check I did was with an LED which displayed the same half cycle output.

Really strange.

Its an audio output from a 4040 going through the 4066 switch.
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JovianPyx



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PostPosted: Tue Oct 16, 2018 9:10 am    Post subject: Reply with quote  Mark this post and the followings unread

This may be a longshot -

Not sure what 555 chip you used - if it's a 7555 or other CMOS 555, then ignore this.

However, if it's a bipolar 555 timer and the 555 is not properly bypassed, it can inject serious current spikes into the PSU whenever pin 3 changes state. These current pulses could easily disturb the logic in the 4017.

This is a well known problem with those older 555 chips.

There are a couple of ways to fix it:

1) Replace the bipolar 555 with a 7555 CMOS 555 equivalent.
2) Apply power to the 555 through an LED, then put a 100 uF electro cap from the 555 power pin to ground. Note that the LED will not light up.

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CHRISKELLY



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PostPosted: Tue Oct 16, 2018 9:31 am    Post subject: Weird 4017 behaviour SOLVED Reply with quote  Mark this post and the followings unread

Embarassed
OK so i tried sending the outputs through another diode to see what happens. And it wouldn't close the switch at all.

So I realised it was a voltage issue. I moved the Vcc connection from a shared breadboard and onto a rail right next to the main power supply.

... And its working again.

So it was the 4066 not being supplied enough Volts to o
Close the switch for a full cycle.

Sorry for wasting your time guys. I feel like Mosc might ban me if I post any more daft problems like this!
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JovianPyx



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PostPosted: Tue Oct 16, 2018 9:51 am    Post subject: Reply with quote  Mark this post and the followings unread

That won't happen. We've all posted "daft" Smile stuff. There is no such thing as a stupid question (except for the one you don't ask). Look what happened by your asking - you discovered the problem and fixed it - and I'd bet you learned something as well which is why we're all here.
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CHRISKELLY



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PostPosted: Wed Oct 17, 2018 12:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Jovian.

Thats good to hear - I've got hundreds of daft questions stored up Laughing
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Steveg



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PostPosted: Wed Oct 17, 2018 3:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Bring 'em on.
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PHOBoS



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PostPosted: Wed Oct 17, 2018 8:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Steveg wrote:
Bring 'em on.




it's not a bad idea to double up on power connections when breadboarding especially if you use the common
(dupont) breadboard wires. Decoupling caps can be helpful as well although I often leave them out when
breadboarding. But if you have a digital circuit that acts a bit odd it could make all the difference.

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