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 Forum index » DIY Hardware and Software
Atari Punk Console with sequencer to multiple inputs
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bcnx



Joined: Jun 19, 2018
Posts: 8
Location: Belgium

PostPosted: Sat Sep 08, 2018 5:40 am    Post subject: Atari Punk Console with sequencer to multiple inputs Reply with quote  Mark this post and the followings unread

Hi all,

I designed an APC circuit with two APCs on it and a step sequencer, which basically cycles through a series of potmeters with a 5V voltage to it.
When I route the sequencer to one discharge pin on the 555 IC, it works fine, but I would like to be able to route it to more potmeters (4 4in total).
When I do that, things stop working.
I figured a solution might be to use a buffering opamp. This does not work however, because the output current is too high. When I lower the current with resistors or voltage dividers, the sounds comes back, but it is different.
What is needed, I think, is a way to copy/buffer the voltage AND current of the sequencer to every 555 discharge input.
Anyone a hint on how to do that?

cheers,

BC

This is the circuit: https://www.circuitsonline.net/forum/file/34912/forum-post
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Sat Sep 08, 2018 10:59 am    Post subject: Reply with quote  Mark this post and the followings unread

welcome party!


Although I think it is possible that could get very difficult. You'd need to make 2 voltage controlled resistors which are then
controlled by the same voltage. You might be able to do this with vactrols/FETs/OTAs but getting them to respond the way
you want will probably be very hard.

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Last edited by PHOBoS on Sat Sep 08, 2018 3:05 pm; edited 1 time in total
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bcnx



Joined: Jun 19, 2018
Posts: 8
Location: Belgium

PostPosted: Sat Sep 08, 2018 1:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Phobos,

I indeed start to get the impression that this is not straight forward.
Someone suggested to change my sequencer principle. I'm no sure at this point, but I think they mean to use the CV input on the 555s and have a sequencer based on VCOs. This would mean however a complete redesign of my circuit, which I'm not really looking forward to, but if that would mean things work the way I want ...


cheers,

BC
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bcnx



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PostPosted: Sat Sep 08, 2018 3:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Phobos,

why actually two voltage controlled resistors? Because each APC ahs two potmeters?

cheers,

BC
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PHOBoS



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PostPosted: Sat Sep 08, 2018 3:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

yeah, using pin 5 is a more standard approach for controlling the frequency of a 555 but will probably sound different
than you have now which has to do with how the pulsewidth is affected.

Quote:
why actually two voltage controlled resistors? Because each APC has two potmeters?

1 for each APC so 2 in total.
edit: I might have misunderstood your initial post now that I read it again, so I guess you need 4 ?

oh I forgot to mention I can't see the schematic (toegang geweigerd) probably have to be logged in for it.

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bcnx



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PostPosted: Sat Sep 08, 2018 3:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

I will upload the schematics here. This is not my schematic but I use the same principle. It shows only one APC and only one potmeter is replaced by a sequencer. I use two APCs and am willing to control 4 pots.

One would thus indeed need four voltage controlled resistors.
The initial design uses 500K potmeters, so I would need voltage controlled resistors in that range. Would FETs or Vactrols be able to do that?
The vactrols on thonk.co.uk only go up to a couple of tens of Kohm.
I found a calculation example for FETs on https://www.youtube.com/watch?v=HEVuVMmMZ6o, but they are also in the same range as the Vactrols are.

cheers,

BC


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bcnx



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PostPosted: Sat Sep 08, 2018 4:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

This seems to be a component that has a wide resistance range:

http://www.mouser.com/ds/2/149/h11f1m-185284.pdf

might have to look into that one,

BC[/url]
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PHOBoS



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PostPosted: Sat Sep 08, 2018 4:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

just be sure: you want to use 1 sequencer and use the same CV to control 4 pots ? Or do you actually want to create
4 seperate CV's (for 10 steps that would need 40 pots in total) but with the same 4017 ? I assume it's the first as the
latter option should just work I think, or you could use 4x 4017 instead.

hmm I just realized that if you would only want to replace 2 pots you could actually make a sequencer with stereo-pots.
I think there are also quad pots (actually I think there are even ones that can be extended in the same way some rotary
switches can) but that would probably get rather expensive. In that case you'd be better of to actually use seperate
pots or even better; completely seperate sequencers.

Maybe there is another option. There are digital pots which are chips that use a digital signal to create a varying resistance.
So it might be possible to first convert the output of the 4017 to a digital signal and use it to control 4 of those. However it
would probably be easier to use an arduino instead of 4017 to control the chips directly which would also give you a LOT of
possibilities for sequencing.

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PHOBoS



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PostPosted: Sat Sep 08, 2018 4:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

bcnx wrote:
This seems to be a component that has a wide resistance range:
http://www.mouser.com/ds/2/149/h11f1m-185284.pdf


ah yes, the H11FxM range. Some people here have experimented with those and I think there is a thread about it
somewhere on this forum.

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bcnx



Joined: Jun 19, 2018
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PostPosted: Sat Sep 08, 2018 5:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Phobos,

the first option, not using 4 times 16 pots Wink

I already contemplated the stereo-pots route, but we then have 2 inputs covered, not 4.
Did not know about quad pots, but as you say, they will too expensive, most certainly as I need 16 pieces.

I also looked at digital potmeters, but that would require, as you state correctly, a microcontroller.

Actually, I start to question if routing the sequencer to several different APC inputs would actually produce so much more interesting sounds. Maybe I just should leave the design as it is: one sequencer, routeable to one input on one APC.

BC
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bcnx



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PostPosted: Sat Sep 08, 2018 5:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

The H11FxM range seems nice, I could use to also sequence other potmeters, like for the PWM part of my circuit.

BC
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PHOBoS



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PostPosted: Sun Sep 09, 2018 11:11 am    Post subject: Reply with quote  Mark this post and the followings unread

You could also use some smaller sequencers for the other pots, even 2 steps could already have some nice effects,
especially when you use different tempos (or divisions). Maybe even audiorate modulation.

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bcnx



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PostPosted: Sun Sep 09, 2018 3:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

My PCB real estate is pretty big as it it is already, but I might indeed consider extras. However, I'd like to get the current problem out of the way first,

cheers,

BC
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