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 Forum index » DIY Hardware and Software » Developers' Corner
Voltage controlled counter or 1-to-8-multiplexer?
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richardc64



Joined: Jun 01, 2006
Posts: 614
Location: NYC
Audio files: 25

PostPosted: Wed May 15, 2013 1:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
I didn't re-read the datasheet in detail, if the inhibit puts the 4051 outputs into high impedance mode you'll want pull down resistors on the outputs to use the inhibit.


Not necessarily. Yes, if the inputs/outputs are being used to mux/demux logic levels, but if used to select/rout analog levels, as in a sequencer, the non-selected pins don't need termination. The ins/outs of the 4051 are analog switches, like the 4066, so the so-called high impedance state is more like open switches than "floating" digital inputs.

I couldn't find the original posting, but below is a schema using 2x 4051 and a 4029.


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Cynosure
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Joined: Dec 11, 2010
Posts: 667
Location: Toronto, Ontario - Canada
Audio files: 34

PostPosted: Wed May 15, 2013 2:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

This method is much easier. Just one chip for the demux.

Phobos made this schematic for me when I made mine.




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analog_backlash



Joined: Sep 04, 2012
Posts: 391
Location: Aldershot, UK
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PostPosted: Wed May 15, 2013 4:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
I couldn't find the original posting, but below is a schema using 2x 4051 and a 4029.

I did look at my schematic today and thought "Did I really need the 4066s?" - obviously not! I built this before I started posting here and I must have learned a few things since then...

Cynosure's/PHOBoS' 4514 solution looks simpler, but this is a gate sequencer, if I've read it correctly, so you would need to add transmission gates in order to produce CVs from this (I think). Please tell me if I'm wrong Very Happy .

Gary
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Cynosure
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PostPosted: Wed May 15, 2013 5:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

The one I built was a gate, but the 4514 outputs Vdd voltage on each step. You can attach a pot to ground on each step instead and use it for CV just like you do with a baby 10.
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elmegil



Joined: Mar 20, 2012
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PostPosted: Wed May 15, 2013 6:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Richard, I had my use of the 4051 going backwards, thinking I needed to wire it like the Baby-10. That's excellent.
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analog_backlash



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PostPosted: Thu May 16, 2013 12:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Cynosure wrote:
The one I built was a gate, but the 4514 outputs Vdd voltage on each step. You can attach a pot to ground on each step instead and use it for CV just like you do with a baby 10.

Thanks for the clarification Cynosure. I've seen a lot of 8- (or 10-) step sequencers based on 4017s in the past, which do include a 4016/4066 switch in the CV output circuitry. I think that I had this as a default "rule" in my mind. As you say, the Baby 10 works without this, so there's no reason why your circuit shouldn't work this way.

Gary
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bunker



Joined: Mar 19, 2009
Posts: 57
Location: Manchester, UK

PostPosted: Thu May 16, 2013 2:38 am    Post subject: Reply with quote  Mark this post and the followings unread

If you really want to use the LM3914 why not use it as nature intended? If the 'fade' is the only real issue then why not hook up 8x LED's and 8xLDR's? That way I'm assuming you can tailor the threshold of the LDR circuit so it switches a transistor on/off when the LED is above/below the 'fade' stage? A bit of a faf I know but it's an alternative to more IC's and should be an easier circuit to understand. Do a search for LDR circuits and you should be able to see how you can control the on/off threshold.
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beep



Joined: May 05, 2013
Posts: 84
Location: Germany

PostPosted: Thu May 16, 2013 2:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think, I'll use the LM3914 in dot mode, because it does exactly what I want
on one chip with low parts count. I still want to quantize a variable control voltage to a defined scale for organic arpeggios from sample&hold sequences and stuff.

But first I have to build something nice for my girlfriend. it's her birthday this month Very Happy

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L´Andratté



Joined: Sep 23, 2012
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Location: Hamburg, Germany
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PostPosted: Tue May 21, 2013 1:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Reminds me of the Doepfer A152 Addressed Switch, which I couldn´t do without... It uses some chips called DG408DJ which seems to be some kind of dedicated 8-stage multiplexer.
http://www.digchip.com/datasheets/parts/dg/parts_dg06.php
Quote from datasheet:"Break-before-make switching action protects against momentary crosstalk between adjacent channels."
They have 2 or 3 in there-

I built my girlfriend an optical metronome, real simple but she´s fond of it with the piano, no more ´tock-tock´
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Dave Kendall



Joined: May 26, 2007
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Location: England
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PostPosted: Thu Jun 06, 2013 5:24 am    Post subject: Reply with quote  Mark this post and the followings unread

There's also the 4067 16-channel mux/demux chip.

cheers,
Dave

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