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CHRISKELLY
Joined: Apr 08, 2018 Posts: 103 Location: England
Audio files: 3
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Posted: Tue Oct 16, 2018 1:09 am Post subject:
Weird 4017 behaviour |
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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
Clock enable tied to ground and it resets correctly.
Any ideas what is happening here?? |
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Steveg
Joined: Apr 23, 2015 Posts: 182 Location: Perth, Australia
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Posted: Tue Oct 16, 2018 5:38 am Post subject:
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??? Circuit? |
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CHRISKELLY
Joined: Apr 08, 2018 Posts: 103 Location: England
Audio files: 3
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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CHRISKELLY
Joined: Apr 08, 2018 Posts: 103 Location: England
Audio files: 3
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Posted: Tue Oct 16, 2018 9:07 am Post subject:
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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
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
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Posted: Tue Oct 16, 2018 9:10 am Post subject:
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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. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
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CHRISKELLY
Joined: Apr 08, 2018 Posts: 103 Location: England
Audio files: 3
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Posted: Tue Oct 16, 2018 9:31 am Post subject:
Weird 4017 behaviour SOLVED |
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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
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
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Posted: Tue Oct 16, 2018 9:51 am Post subject:
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That won't happen. We've all posted "daft" 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. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
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CHRISKELLY
Joined: Apr 08, 2018 Posts: 103 Location: England
Audio files: 3
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Posted: Wed Oct 17, 2018 12:35 am Post subject:
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Thanks Jovian.
Thats good to hear - I've got hundreds of daft questions stored up |
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Steveg
Joined: Apr 23, 2015 Posts: 182 Location: Perth, Australia
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Posted: Wed Oct 17, 2018 3:25 am Post subject:
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Bring 'em on. |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Wed Oct 17, 2018 8:15 am Post subject:
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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. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
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