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 Forum index » DIY Hardware and Software » Musical Interfaces
DIY ribbon
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frijitz



Joined: May 04, 2007
Posts: 1712
Location: NM USA
Audio files: 54

PostPosted: Sun Apr 21, 2013 9:51 am    Post subject: Reply with quote  Mark this post and the followings unread

KnobHell wrote:
Will your electronics work with the kurzweil ribon?

Hi Len,

I really don't know enough about it to say. If its brain is in the unit itself, then no. But if the raw signals are on the cable, then maybe.

Ian
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KnobHell



Joined: Jan 28, 2012
Posts: 58
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PostPosted: Sun Apr 21, 2013 1:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

HI Ian,

It is just a "raw" ribbon controller.

Here is the info on the ribbon it self from the modular synthesis site:

http://modularsynthesis.com/cvs/cvs3.htm

The PC2SRIB ribbon is actually comprised of three segments which interface to IN-2, IN-3, and IN-4. The ribbon measures 6K5 ohms total which would be ~20K each for the individual ribbon segments. I measured the voltage to the ribbon from my Expressionmate controller which consisted of five ~1 mS 5 volt pulses followed by 5 mS of 0 volts at a cycle frequency of ~100 Hz. The CVS powers the ribbon at 5.6 volts from OUT-4 with a diode in series between the ribbon and ground. I do not know the power capability of each ribbon segment so I keep the power in each segment to a low 1.25 mW dissipation.


len
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frijitz



Joined: May 04, 2007
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PostPosted: Sun Apr 21, 2013 6:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

KnobHell wrote:
Here is the info on the ribbon it self from the modular synthesis site:
http://modularsynthesis.com/cvs/cvs3.htm

I'm having trouble understanding that writeup. Aren't the three sections in series? Then the individual sections would be 6.5k/3, not 20k. I don't see how the sections could possibly be connected in parallel. Can you make a diagram showing the three resistive sections, their resistances, how they are connected to each other and how they are connected to the pins?

Ian
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davebr



Joined: Jun 09, 2007
Posts: 193
Location: portland, or

PostPosted: Sun Apr 21, 2013 7:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
KnobHell wrote:
Here is the info on the ribbon it self from the modular synthesis site:
http://modularsynthesis.com/cvs/cvs3.htm

I'm having trouble understanding that writeup. Aren't the three sections in series? Then the individual sections would be 6.5k/3, not 20k. I don't see how the sections could possibly be connected in parallel. Can you make a diagram showing the three resistive sections, their resistances, how they are connected to each other and how they are connected to the pins?

Ian

The three sections are in series physically but in parallel electrically. I will use "potentiometer" language since it is easy to visualize. The three potentiometers all share common end connections (2) and then the individual wipers (3) are brought out for a total of 5 connections with 1 unused. The middle potentiometer is reversed left to right as well (think of it as the end connections swapped).

Which common end you use for ground and Vcc depends on whether the cable exits from the left or right and what direction you want to increase the output voltage. I chose mine with the cable on the left so the connections for Vcc and Ground result in increasing voltage in the outer two ribbon segments when sliding to the right. It is reversed for the middle segment with decreasing voltage when sliding to the right.

So, to make a single continuous ribbon, you need to offset and reverse the middle ribbon to stack it on the end of the left ribbon, and then offset the right ribbon to stack in on the end of the middle ribbon.

I labeled the pinout on my page by what connection they make to the CVS. The specific Ribbonmate wiring is in the parenthesis, but explicitly it is:
Pin 1 no connection
Pin 2 wiper of the right ribbon segment
Pin 3 wiper of the left ribbon segment (cable end)
Pin 4 wiper of the middle ribbon segment
Pin 5 common end of ribbons (used for ground for increasing voltage to right)
Pin 6 common end of ribbons (used for +5V for increasing voltage to right)

As with potentiometers, the minimum and maximum voltages were not 0 and Vcc so I had to experiment with my offset values in software to make the three segments very piecewise smooth. You can probably figure them out in the code. Mine are much better than the standard Kurzweil implementation, but I suspect each ribbon is a bit different.

The reason I was concerned of the resistance is I was trying to figure out what voltage to use across the ribbon. I have no idea of the power capability of the resistive strip and so verified a +5V pulse from their controller. At ~20K each at 5V the power dissipated is only 1.25 mW each segment so I left the +5.6V powered on continuously instead of pulsed when I read the output voltage (IIRC).

Hope this helps

Dave
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KnobHell



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PostPosted: Sun Apr 21, 2013 8:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ian,

Here is what I found. There are three independent sections. Right, mid, left. Each wiper goes between about 25 ohms and 3.672 k, end to end on each segment. Interestingly enough before you get to the end the resistance goes up to 4k, maybe at 80%. As in the schematic the mid section is the reverse of the right and left sections. Meaning that it's wired backwards in relation to those two.

The resistance between gnd and V+ is 3.672 ohms.

Not sure that being segmented would be as useful as one linear ribbon.

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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KnobHell



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PostPosted: Sun Apr 21, 2013 8:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

They are open unless pressed. Just used pots for convenience.
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davebr



Joined: Jun 09, 2007
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PostPosted: Sun Apr 21, 2013 8:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

KnobHell wrote:
Not sure that being segmented would be as useful as one linear ribbon.
I got them very piecewise smooth, much better than the Kurzweil. You need to be able to "offset" each segment specifically (probably each ribbon is a bit different). You would probably have to then scale the entire ribbon if you wanted a specific range. Easy to do in software.

Dave
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frijitz



Joined: May 04, 2007
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PostPosted: Sun Apr 21, 2013 8:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks very much, guys. I appreciate your effort in clarifying. I think the discontinuities are going to be a killer for an analog implementation. But I'll think about it some more.

Ian
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davebr



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PostPosted: Sun Apr 21, 2013 9:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
Thanks very much, guys. I appreciate your effort in clarifying. I think the discontinuities are going to be a killer for an analog implementation. But I'll think about it some more.

Ian
I initially did a design all in analog. It wasn't that tough but it was more hardware than I wanted to hand wire. The offsets are easy as you can make them adjustable for the two segments to line them up. You can add an overall scale factor as well. It just took more circuitry to generate a gate or trigger from the ribbon pressed and I wanted a mode where the ribbon would "hold" the last press. Now you are starting to get into even more circuitry. It wouldn't take much to implement it in an AVR or PIC. I have all my basic code published and those stamps aren't that much either.

It does make for a nice ribbon. - Dave
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frijitz



Joined: May 04, 2007
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PostPosted: Sun Apr 21, 2013 9:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

davebr wrote:
I initially did a design all in analog. It wasn't that tough but it was more hardware than I wanted to hand wire. The offsets are easy as you can make them adjustable for the two segments to line them up. You can add an overall scale factor as well. It just took more circuitry to generate a gate or trigger from the ribbon pressed and I wanted a mode where the ribbon would "hold" the last press. Now you are starting to get into even more circuitry.

I now have circuitry that holds reliably on finger up. But I wouldn't want to build it three times! So it would have to work off the combined signal from the three sections. Probably doable, but again the transition points could cause some trouble.

Ian
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KnobHell



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PostPosted: Mon Apr 22, 2013 5:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Does anyone make a commercially available one segment equivalent?

The form factor is really nice on the kurzweil, I'd like to find something like that.
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frijitz



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PostPosted: Mon Apr 22, 2013 6:50 am    Post subject: Reply with quote  Mark this post and the followings unread

KnobHell wrote:
Does anyone make a commercially available one segment equivalent?
The form factor is really nice on the kurzweil, I'd like to find something like that.

How wide is the ribbon -- the actual active part?

Ian
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KnobHell



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PostPosted: Mon Apr 22, 2013 7:52 am    Post subject: Reply with quote  Mark this post and the followings unread

I would guess possibly 1/2 inch.

22 inches over all. Around 7 3/4 per section.
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