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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
CD4031 tap looper...
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cyclic



Joined: Mar 15, 2015
Posts: 90
Location: hobart

PostPosted: Thu Dec 19, 2019 6:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

yep, I'm pretty sure I got it then!

If I have time to PCBify something for the original tap-looper I'll
- check here with schematics etc so its checked over
- make sure I make it small enough to either get 2 on a 10x7 or make it fairly easy to chain them together.

I don;t think I'll be doing that 63step cv sequencer even though I understand it now and reckon its a pretty inspired idea, but by doing the above it should make it easier to use anything I do for it.
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dadinfinitum



Joined: Dec 16, 2019
Posts: 24
Location: Maryland, US

PostPosted: Sun Sep 13, 2020 7:29 am    Post subject: Reply with quote  Mark this post and the followings unread

I have tried to get both PHOBoS's simpler version and this version, but I can't get either of them to work. I've double and triple checked my circuit on the breadboard!
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dk



Joined: Feb 12, 2019
Posts: 59
Location: Europe

PostPosted: Sun Sep 13, 2020 7:49 am    Post subject: Reply with quote  Mark this post and the followings unread

How are you testing it? Do you have a LED strapped across the output to see what's coming out?

It's a 64 step sequence, so if you use a slow clock, and can take a while for the chip to spit out what you've input.

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dadinfinitum



Joined: Dec 16, 2019
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Location: Maryland, US

PostPosted: Sun Sep 13, 2020 9:02 am    Post subject: Reply with quote  Mark this post and the followings unread

dk wrote:
How are you testing it? Do you have a LED strapped across the output to see what's coming out?

It's a 64 step sequence, so if you use a slow clock, and can take a while for the chip to spit out what you've input.


I have the output as a gate for a 40106 osc. Also using a 40106 osc (albeit a slower one) for the clock. I have LEDs on both of those. Also using a multimeter on both the data in and the data out.
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dk



Joined: Feb 12, 2019
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Location: Europe

PostPosted: Wed Sep 16, 2020 4:08 am    Post subject: Reply with quote  Mark this post and the followings unread

How about when you have the output disconnected and you just hang a LED and dropping resistor off of it?

These circuits are really simple, so it's likely that either you have a big error somewhere that doesn't want to be seen or you have a bad chip.

For what it's worth, I built 2 of the more complex versions and they work fine. I've attached my stripboard layout, in case it helps. You can ditch the voltage regulator and associated parts if you don't need them, and directly attach your voltage to the trace BELOW gnd. Also, beware on the right side than I have 2 jumpers sharing the same hole (not very elegant, but whatever).


4031 Tap-A-Loop.png
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4031 stripboard
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4031 Tap-A-Loop.png



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dadinfinitum



Joined: Dec 16, 2019
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PostPosted: Wed Sep 16, 2020 5:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, it seemed pretty simple, which is why I've been surprised it hasn't worked. I'll see if I can emulate your stripboard.
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dadinfinitum



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PostPosted: Wed Sep 16, 2020 7:09 am    Post subject: Reply with quote  Mark this post and the followings unread

So, still no luck. The LED at the end doesn't light up, and the oscillator that is using the output as a gate doesn't activate. Using my scope on the output, it looks constantly high? Which is really weird.


IMG_20200916_100058_1.jpg
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IMG_20200916_100058_1.jpg



IMG_20200916_100759.jpg
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dk



Joined: Feb 12, 2019
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Location: Europe

PostPosted: Wed Sep 16, 2020 7:27 am    Post subject: Reply with quote  Mark this post and the followings unread

Hard to tell from the pic, but it looks like you haven't grounded the chip? Pin 8 should go to ground, while pin6 should connect with pin 10 and your output..

EDIT: I was under the impression that between pins 6 and 8 there was a loop, but that's probably just the picture cutting it that way.

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dadinfinitum



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PostPosted: Wed Sep 16, 2020 8:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry, that picture was mostly to identify the chip. Here's a better picture (pin 8 is grounded via row 27, and pin 10 to pin 6 via row 41).


IMG_20200916_105812.jpg
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PHOBoS



Joined: Jan 14, 2010
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Location: Moon Base
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PostPosted: Wed Sep 16, 2020 11:07 am    Post subject: Reply with quote  Mark this post and the followings unread

From what I can tell that looks ok.
You could try the bare minimum to see if the chip does anything at all:

pin1: GND
pin2: fast (KHz) oscillator input
pin3: NC
pin4: NC
pin5: NC
pin6: output
pin7: NC
pin8: GND

pin9: NC
pin10: GND
pin11: NC
pin12: NC
pin13: NC
pin14: NC
pin15: slow oscillator input
pin16: V+


If the CLK (2) frequency is fast enough the output (6) should pretty much follow the oscillator on the input (15).

Also move the chip to another part of the breadboard.

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dadinfinitum



Joined: Dec 16, 2019
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Location: Maryland, US

PostPosted: Wed Sep 16, 2020 5:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

Good news: it works. Now to figure out what's wrong with the circuit. I even read through the datasheet and the CMOS cookbook to try and troubleshoot/test other configurations.
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dadinfinitum



Joined: Dec 16, 2019
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PostPosted: Thu Sep 17, 2020 12:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

I got the circuit to work!

The only issue: it starts high, so I have to hold erase through a cycle to clear it. I tried pulldowns on the write and erase switches, but nothing. Thoughts on that?
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Thu Sep 17, 2020 1:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

cheers good to hear it works

shiftregisters and a lot of other CMOS chips often start up in a random state so unless it has a reset input there isn't much you can do about it.
I guess you could add an extra switch which enables a fast CLK and pulls the data input low at the same time

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dadinfinitum



Joined: Dec 16, 2019
Posts: 24
Location: Maryland, US

PostPosted: Thu Sep 17, 2020 4:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

If an easy solution is just "start in erase mode," then that's fine. (I'm using a traditional toggle switch for erase, and a keyboard switch for tapping)
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dk



Joined: Feb 12, 2019
Posts: 59
Location: Europe

PostPosted: Sat Sep 19, 2020 5:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Glad to see you got it working! I have two in my rig, one of which starts up empty, the other full. It's a bother, but not enough for me to fix it Laughing
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