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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Control Voltage Mixing Module
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nathanxl



Joined: Apr 24, 2012
Posts: 73
Location: Wa

PostPosted: Fri Jun 08, 2012 8:33 am    Post subject: Control Voltage Mixing Module
Subject description: 4 Lunetta signals in - 1 CV out
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Hello.
Havent been able to find a definate answer to my newbie question. Sorry if has been covered before.

I want to make a module where I can patch 4 gates/signals from seperate lunetta modules into it and this module would mix them down and spit out a control voltage that I can use with my regular modular synth gear.
No need to worry about tuning or attenuation but some protection of some sort so no spikes fry my pricey gear would be good.
Maybe with a slew feature to smooth out the square wave steps if its easy for someone with limited skilz...

Any idea where I can find a simple schematic or any tips on how to pull this off would be ace.
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Uncle Krunkus
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PostPosted: Fri Jun 08, 2012 9:59 am    Post subject: Reply with quote  Mark this post and the followings unread

I would just put the 4 signals into an R/2R network. 4 bits would give you a resolution of 16 steps. To "slew" between them, include an op-amp stage with a cap in the feedback path (I think? Help me Les! Laughing )
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JingleJoe



Joined: Nov 10, 2011
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PostPosted: Fri Jun 08, 2012 12:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yup, the R2R ladder as suggested by Uncle K is a digital to analogue converter Smile
Uncle Krunkus wrote:
To "slew" between them, include an op-amp stage with a cap in the feedback path (I think? Help me Les! Laughing )

You can just include a passive low pass filter on the output, that works too.

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nathanxl



Joined: Apr 24, 2012
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PostPosted: Sun Jun 10, 2012 7:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Ive seen this R/2R ladder DAC bandied about and am thankful you clarified that it is infact what I need in this application. I am however a noob that requires some hand holding it would seem, sorry.
I have done some googling and searching here, have gathered that I need two different resistor values for the ladder, have seen a lot of mathematical equations to work out these values but my brain froze trying to recall what my highschool teacher was yelling about all those years ago...
R2 being double the value of R1 I cannot find clear enough directions on what I actually need for my particular application. I feel somewhat guilty and embarressed about showing my ineptitude but I know this is a friendly place.
Im running my lunetta on a single 9VDC psu and the opamp buffer I will use on the back end of this R/2R ladder will tap into this psu...
I require the output CV from this ladder to be in the range of 0V to 5V at around 50kohms for my other gear.
I am yet to experiment with this on a breadboard yet but will head out to purchase resistors to do it in the next day or two.
Can anyone shed some light on what resistor values I should buy to play around with?
You guys are great, thanks in advance.
Also with the slewing, Id like to have its effect pot controllable.
Cheers
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JingleJoe



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PostPosted: Sun Jun 10, 2012 10:01 am    Post subject: Reply with quote  Mark this post and the followings unread

nathanxl wrote:
Ive seen this R/2R ladder DAC bandied about and am thankful you clarified that it is infact what I need in this application. I am however a noob that requires some hand holding it would seem, sorry.
I have done some googling and searching here, have gathered that I need two different resistor values for the ladder, have seen a lot of mathematical equations to work out these values but my brain froze trying to recall what my highschool teacher was yelling about all those years ago...

you can just throw in almost any values if you aren't worried about accuraccy, 100k and 220k are pretty close to the values required, 330k and 680k are too. Use whatever you have to hand, just remember don't go too low, you don't want to overstress your CMOS outputs with something ridiculously low like a ladder made from 10 ohm and 22ohm resistors Rolling Eyes

Quote:

I require the output CV from this ladder to be in the range of 0V to 5V at around 50kohms for my other gear.
[...]
Can anyone shed some light on what resistor values I should buy to play around with?
You guys are great, thanks in advance.

No problem, my cause is to further the weird sounds in the world Smile
I would make an op-amp amplifier, of the non-inverting variety. You could do a lot of reading to simplify things a bit for yourself here Wink or just look up the standard non-inverting op amp amplifier, then you can use it to attenuate the signal from your R2R ladder to be a lower voltage. Most A to D converters I see have that amplification stage tacked on the end to scale the voltages you get out of it.

Quote:

Also with the slewing, Id like to have its effect pot controllable.
Cheers

exchange the resistor in the standard low pass filter for a potentiometer and you have a variable slewificator. Smile Might be an idea to put the pot in series with a low value resistor.

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jcintheus



Joined: Oct 16, 2011
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PostPosted: Sun Jun 10, 2012 3:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

You can use all the same value resistors.
Use two in parallel for "R" and one for "2R".
Or, use one for "R" and two in series for "2R".
This makes it easier to get the proper ratios with what you may have on hand.
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nathanxl



Joined: Apr 24, 2012
Posts: 73
Location: Wa

PostPosted: Mon Jun 11, 2012 6:21 am    Post subject: Reply with quote  Mark this post and the followings unread

jcintheus wrote:

Or, use one for "R" and two in series for "2R".


This is what I did today with some resistors I had laying around... It worked and Im extremely happy.
I am constantly surprised how easy this stuff actually is with just a little effort what Im also super excited about is that with a little help from you guys in this fabulous forum I will be able to make the objects in my head a physical reality.
Thankyou
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wolfdog



Joined: Jun 12, 2012
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Location: Colorado

PostPosted: Tue Jun 12, 2012 7:58 am    Post subject: Reply with quote  Mark this post and the followings unread

looking forward to following w/great enthusiasm
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JingleJoe



Joined: Nov 10, 2011
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PostPosted: Tue Jun 12, 2012 8:24 am    Post subject: Reply with quote  Mark this post and the followings unread

http://electro-music.com/forum/topic-50859.html
Too sleep deprived for lots of words; Observe, for I have done a similar circuit before.

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nathanxl



Joined: Apr 24, 2012
Posts: 73
Location: Wa

PostPosted: Tue Jun 12, 2012 7:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Will solder everything up today and work on a slew module. Have found a schematic for smooth glide/slewing here:
http://www.sdiy.org/pinky/data/bin5schem.pdf
The two op amps in the bottom right corner around P5; the 1M pot...

Here is a vid of its first run spitting out CV.

Fun stuff.
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