CD4031 tap looper...

cyclic · Joined: Mar 15, 2015 Posts: 95 Location: hobart

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.

dadinfinitum · Joined: Dec 16, 2019 Posts: 40 Location: Maryland, US

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!

dk · Joined: Feb 12, 2019 Posts: 115 Location: Europe

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.

dadinfinitum · Joined: Dec 16, 2019 Posts: 40 Location: Maryland, US

dk · Joined: Feb 12, 2019 Posts: 115 Location: Europe

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

Description:

4031 stripboard

Filesize:

141.04 KB

Viewed:

396 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

dadinfinitum · Joined: Dec 16, 2019 Posts: 40 Location: Maryland, US

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.

dadinfinitum · Joined: Dec 16, 2019 Posts: 40 Location: Maryland, US

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

Description:

Filesize:

3.1 MB

Viewed:

351 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

IMG_20200916_100759.jpg

Description:

Filesize:

2.54 MB

Viewed:

349 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

dk · Joined: Feb 12, 2019 Posts: 115 Location: Europe

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.

dadinfinitum · Joined: Dec 16, 2019 Posts: 40 Location: Maryland, US

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

Description:

Filesize:

2.68 MB

Viewed:

346 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

PHOBoS · Posted: Wed Sep 16, 2020 11:07 am Post subject:

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.

dadinfinitum · Joined: Dec 16, 2019 Posts: 40 Location: Maryland, US

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.

dadinfinitum · Joined: Dec 16, 2019 Posts: 40 Location: Maryland, US

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?

PHOBoS · Posted: Thu Sep 17, 2020 1:48 pm Post subject:

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

dadinfinitum · Joined: Dec 16, 2019 Posts: 40 Location: Maryland, US

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)

dk · Joined: Feb 12, 2019 Posts: 115 Location: Europe

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

zaphod betamax · Joined: Nov 27, 2020 Posts: 47 Location: sarnia

Don't forget about the CD4517.
Available at digikey.ca and other places

Estebandito

My version of the tap looper. It is pretty much the most basic version, with an external clock input as well as an inbuilt clock (with cap switch, and pulse/gate switch). Outputs are Q, inverted Q. Also there are two outputs from the 7-segment display drivers and one where I send those outputs through a NAND gate.

107D751F-9F0C-4179-9C31-B5DCD2600454.jpeg

Description:

Filesize:

3.22 MB

Viewed:

121 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

trim.0FC2BD09-614E-4ABB-ACEA-776483BC81C5.MOV

Description:

Download

Filename:

trim.0FC2BD09-614E-4ABB-ACEA-776483BC81C5.MOV

Filesize:

52.12 MB

Downloaded:

307 Time(s)

PHOBoS · Posted: Sun Dec 20, 2020 7:16 am Post subject:

veyr cool build Very Happy

what did you use to drive the displays ?

Estebandito · Posted: Sun Dec 20, 2020 8:35 am Post subject:

Two 4026’s. They are meant to drive common cathode displays but I only had common anode ones, so each display output is hooked up to a transistor with the collector connected to the display and the emitter to gnd. It works but I don’t recommend it unless you don’t mind lots of additional soldering. Razz

I forgot to mention I also used two 4017’s to limit the count to 63 (not 64 as the counter starts at 00). The photo shows the 4026’s, a 4093 (used for the clock and the erase button), and two 4017’s. So apart from the 4093 this is just to make the counter work, I hadn’t even put the 4031 in there yet.

8A69DF21-366A-4233-862F-F724AEC650B0.jpeg

Description:

Filesize:

4.27 MB

Viewed:

115 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

PHOBoS · Posted: Mon Dec 21, 2020 6:12 am Post subject:

ah, a combined counter+display driver. Main reason I asked is because it can be tricky to control more than 1 display
with some logic chips, at least from a seperate counter. It's a nice idea those displays.

Estebandito · Posted: Mon Dec 21, 2020 8:23 am Post subject:

This is my first use of 7-digit displays and drivers and they seem to be working fine. The only issue with this module is that the 4031 output sometimes goes high and stays high until the power has been switched off for a while. As far as I can tell this happens when pushing the write data button when the output is high.

dk · Joined: Feb 12, 2019 Posts: 115 Location: Europe

I'm finally getting around to de-bouncing my switches and was thinking of adding a data input (since I'll have left over 40106's anyway).

Does anyone see anything wrong with this, before I tear into the module? ( besides not using a logic gate for the switch, of course Very Happy

)

Edit: Sorry, I should have written that my build is PHOBoS' deluxe version.

tap-a-loop logic input.png

Description:

Filesize:

35.09 KB

Viewed:

107 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

dk · Joined: Feb 12, 2019 Posts: 115 Location: Europe

Just an update to the previous post. I updated it so that the switch is AND gated with the data input and also added the switch debouncing circuit. I haven't breadboarded it yet, but theoretically it should work?

tap-a-loop logic input complete.png

Description:

Filesize:

80.24 KB

Viewed:

102 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

PHOBoS · Posted: Thu May 20, 2021 7:44 am Post subject:

I'm not sure if that does what you want it to do. When the data enable switch is connected to GND, DIN1 is low and DIN2 is high,
which doesn't do anything so that would be ok I assume. Now if the data enable switch is connected to V+ (or not connected,
doesn't matter) and your data input is high then DIN1 is high and DIN2 is low. Which is the equivalent of pressing both the write
and erase button at the same time. I'll have to check the datasheet again to see what that does but I would think that you either
want to write a bit or erase a bit, not do both at the same time. If I ignore the CD4031 and just look at what would happen with
the output then U2c would be low, U2b would be high and as a result U2d and U2a would be low.

dk · Joined: Feb 12, 2019 Posts: 115 Location: Europe

Oh, you're right!

The momentary at the top is just the write switch. I was hoping (with the now-obviously incorrect bottom section) to be able to enable and disable the data input without interfering with the buttons. Do you have any ideas how to accomplish this? My first thought was to use a switch (4066), but I was trying to skimp on using an extra chip .... or perhaps I need to?