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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Automated voltage divider thingy
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Estebandito



Joined: Dec 25, 2017
Posts: 19
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PostPosted: Tue Apr 26, 2022 12:38 pm    Post subject: Automated voltage divider thingy
Subject description: something I’m wiggling on
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Hey everyone, just before leaving the studio today I threw together this thing on the breadboard. It’s a simple idea for an automated voltage divider. I put it together as a starting point for my next studio session and I haven’t actually tried using it yet. Looks like I need to amp the output before it is at all useable, or use smaller resistances? what do you think? I think I will try using this double mux thing in an oscillator as well.


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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Tue Apr 26, 2022 5:57 pm    Post subject: Re: Automated voltage divider thingy
Subject description: something I’m wiggling on
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Estebandito wrote:
Hey everyone, just before leaving the studio today I threw together this thing on the breadboard. It’s a simple idea for an automated voltage divider. I put it together as a starting point for my next studio session and I haven’t actually tried using it yet. Looks like I need to amp the output before it is at all useable, or use smaller resistances? what do you think? I think I will try using this double mux thing in an oscillator as well.


A couple of notes if you want to use it as drawn,. so connected between GND and +5V.
If you set both muxes to address 111 you are basically creating a direct short through the 2 chips which they probably won't be too happy with.
Also at the moment you have 6-bits as an input which in theory could give you 64 different voltages but in this configuration there are some
duplicates, for example if the address is the same for both muxes. (assuming all the resistors have the same value). This isn't necessarily a bad
thing though and honestly I am kinda curious what the levels and distribution of those would be.

I am actually currently working on a circuit that is half of that (1 mux + resistors) to use as a DAC, though it's wired up a bit differently.
That first circuit you drew is basically a DAC, be it a bit of an odd one. I do like how you approached this and how each mux is one half
of a voltage divider but adjustable, so it is like having 2 potentiometers in series. Could be interesting depending on how you control it.
I guess you could do a similar thing with 2 R2R resistor ladders.

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Estebandito



Joined: Dec 25, 2017
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Location: Amsterdam
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PostPosted: Wed Apr 27, 2022 12:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
If you set both muxes to address 111 you are basically creating a direct short through the 2 chips which they probably won't be too happy with.


You’re right. I could add a resistor to the +5v input, but wiring the chips up differently and using all different resistors is actually more interesting because I’d more easily avoid the duplicates.

One of the things I want to use this for is to drive a vactrol.

I am expecting the 4069 to work to beef up the output level, otherwise a 358?


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This is a version I didn’t test but I assume it works, and this is probably similar to the design you mention you are working on?
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PHOBoS



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PostPosted: Wed Apr 27, 2022 6:38 am    Post subject: Reply with quote  Mark this post and the followings unread

yes using different resistor values can make it more interesting,. I bet there is a way of using certain ratios
that results in the max amount of diffent combinations but it can also be fun to just grab whatever you have.
Of course you could use potentiometers but then you're probably going to end up with a sequencer.

Not sure if the 4069 is very suitable for this,. I never experimented much with it as an opamp but
I believe its range is rather limited. For driving a vactrol you'll have to experiment anyway as it's
not so easy to control a LED with a voltage (current would work better) and the repsonse of a vactrol
itself is far from linear. Vactrols can sound nice if you use them to control the frequency of an oscillator.


The DAC idea I am working on uses a resistor string between a reference voltage and GND and the mux
just selects a voltage from that. However I also designed and tested an R2R version which has a much lower
component count and is a bit more versatile. It's a bit less accurate but has the advantage that you can plug
in analog signals directly and it will just function as a mixer with a fixed ratio between the inputs.


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PHOBoS



Joined: Jan 14, 2010
Posts: 5394
Location: Moon Base
Audio files: 699

PostPosted: Wed Apr 27, 2022 12:35 pm    Post subject: Re: Automated voltage divider thingy
Subject description: something I’m wiggling on
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PHOBoS wrote:
I am kinda curious what the levels and distribution of those would be.

I couldn't resist so here's the list of voltages assuming all resistors have the same value and the muxes don't have any internal resistance.

5.000, 5.000, 5.000, 5.000, 5.000, 5.000, 5.000
4.375
4.286
4.167
4.000
3.889
3.750, 3.750
3.571
3.500
3.333, 3.333, 3.333
3.182
3.125
3.000, 3.000
2.917
2.857
2.778
2.727
2.692
2.500, 2.500, 2.500, 2.500, 2.500, 2.500, 2.500
2.308
2.273
2.222
2.143
2.083
2.000, 2.000
1.875
1.818
1.667, 1.667, 1.667
1.500
1.429
1.250, 1.250
1.111
1.000
0.833
0.714
0.625
0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000

which gives you 37 unique values.


it might be interesting to control one or both of the muxes at audio rates and us it as a waveform generator.


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