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 Forum index » DIY Hardware and Software » Musical Interfaces
Guitar fretboard as CV controller?
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nofrets



Joined: May 10, 2008
Posts: 29
Location: Hills of West Virginia

PostPosted: Sat May 10, 2008 1:49 pm    Post subject:  Guitar fretboard as CV controller? Reply with quote  Mark this post and the followings unread

Hi all -

What would be the possibility of using a guitar-ish device as an analog controller? Could the frets be wired into a resistance network (not sure if that's the right term) and the circuit be closed by the string? Are the voltages low enough for this to be safe? I know some early synth guitars used microswitches in the neck, but that seems excessively complicated. I'm thinking of something with three strings, tuned like an Oud or strumstick, but able to control a synth as well.

TIA!

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Stream Operator


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PostPosted: Sat May 10, 2008 4:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi nofrets, and welcome to electro-music.com. I am working on a Human Interface Device for a guitar that will sense the angle of the guitar with respect to the gravity reference. The HID will plug into the USB port and the computer can then know the angle. That way the computer can create three control voltages (in digital form) and control synth-like effects with them.

So when you point the guitar at the audience you get more feedback, or when you point it up you get reverb, for example. There are lots of other things that I will do with it too, but you get the idea. Is that along the lines of what you are thinking?

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nofrets



Joined: May 10, 2008
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PostPosted: Sun May 11, 2008 6:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Not exactly, although I read your thread and think that's a very cool idea. I'm thinking something lower-tech, using the string(s) and frets as the contacts in a circuit like Ray Wilson's single buss keyboard controller.

What I don't have the experience/knowledge to figure out is (1) is the current low enough to be safe and (2) how to make it high-note priority vs. low-note.

I suppose I could move this thread to the MFOS forum, but I thought I'd fish here first.

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PostPosted: Sun May 11, 2008 9:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh, now I got you! If I wanted to do that, I'd buy one of the circuit boards rather than try to redesign it myself, and then I'd make those moving wires be fixed on the frets and attach the sensor line to the strings. I don't know, but I presume that all of the strings are one node since the tremelo bar is metal, but I don't have a guitar to look at right now.

Anyway, it's a reverse-action switch mechanism on the guitar, as compared to the keyboard, where you press the sensor node down to touch the metal contacts on the frets. To make those contacts, I would use copper tape which you can solder to, and run the string of resistors up the neck of the guitar. The tape will conform to the shape of the fret, and it's thick enough to be durable. Copper tape is used for making stained glass and any local stained glass house will have it in various widths, plus they have tape reel holders and x-acto knives which you'd need to cut the tape.

The currents are low, you've got a total of about 6 kOhms driven by 12 Volts, so we are talking about a current in the ballpark of 2mA. Unfortunately that's enough to stop your heart if by some amazing coincidence the current happened to flow directly through your heart. Of course the resistance of the skin will protect you in all normal circumstances but if you have cuts or worn spots from playing the frets on your fingers, it could by some bizarre stretch of the imagination possibly cause 2 mA or more to flow through your body.

What I would do to reduce that is to multiply all the resistances by 10 in the sensor string, the current source, and the sensor charging circuit. Then you only have 200 uA flowing which should be safer. It's just a precaution. Of course, you'd never get the product approved for consumer use if you have electrical signals in contact with the human body, but for a DIY project it would be just fine.

Overall It looks like a really cool idea. Let us know if you build it!

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nofrets



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PostPosted: Sun May 11, 2008 12:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Fantastic! That's the info I was looking for. I was planning on starting with the MFOS kit. I think I understand what you mean about upping the resistances, would you be willing to review a revised schematic before I start building?

Also, any ideas on how to make it high-note priority vs. low note? Seems that would be more logical on a fretted instrument.

Thanks!

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PostPosted: Sun May 11, 2008 12:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Coolness, just post your schematic as a jpg file and it will show up so we can review it for you. Um, as far as differentiating high and low notes, I think you mean differentiating the strings. That would be possible, but I'd prefer to keep it simple and just go with the closest thing that we can to the author's schematic. If we over complicate it then you'll have unsuccessful results and be disappointed.

In fact, I'd suggest not making the guitar neck part first but instead make a string of resistors with copper foil tape contacts on a piece of plastic or wood first. That way debugging your circuit and creating the haptic interface are separate so you can "divide and conquer" the process. Good luck!

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nofrets



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PostPosted: Sun May 11, 2008 2:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

We might be talking about two different things here. I envision this as a 2 or 3 string instrument, with only one of the strings generating a CV. It just seems, as a half-a$$ guitarist, that high-note priority would feel more natural than low-note.
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PostPosted: Sun May 11, 2008 4:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, you'll get a different CV for each fret position. If the strings are all one electrical node, that is, they are shorted together, then you'll get it regardless of which string is plucked. If you have electrically separate strings, then you *could* create a separate CV for each string by duplicating the receiver circuit for each string and combining them somehow. But why? just let the strings be shorted together as they naturally are. If I still don't get it, please explain further and maybe then it will sink into my skull, haha. Keep on truckin'!
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blue hell
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PostPosted: Sun May 11, 2008 4:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Inventor wrote:
If you have electrically separate strings


The strings will short on the frets, unless you split those up and add diodes to each and all sub frets and then read out out the whole thing as a digital keyboard matrix.

The idea to have only one "electric string" is simpler to make, and it could use just a resistor string, as was mentioned in an earlier post.

There would be no need to have 12V over the resistor string, as a guitar string just spans one and a half octave or something and as the normal voltage would be one per octave it would always be less than 2V, nothing to worry about for safety as long as it's well isolated from any mains connection. The current flowing through the resistors has nothing to do with the potential current flowing through a hearth muscle, a badly isolated connection to some mains voltage could be lethal of course.

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also .. could someone please turn down the thermostat a bit.
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TheShaggyDA



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PostPosted: Sat May 17, 2008 3:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Greetings Smile

First time post here, and this post caught my eye. I'm currently building a guitar synth, got a 4 string proof of concept board working, and I'm shortly going to put it in a real guitar neck. When it's finished, I'll post the full details, but in the meantime here's a few piccies of the fretboard. I've split the frets, and each string is a simple resistor chain.

I'm using the gubbins from a joystick for the controller, conencted via USB to my laptop, where I've written a C# routine for conversion to MIDI.

I'm still working on the triggering - I've got 8 analogue channels to play with and 36 digital in my controller, so I could either go for 4 strings + pitchbend, modulation & volume on the analogue with digital triggering, or use 4 of the channels for velocity sensitive triggering via piezo transducers. I'm kind of making it up as I go along, so will probably go through a number of configurations before I settle on the final design.


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PostPosted: Sat May 17, 2008 6:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wow, rock on ShaggyDA, that looks awesome! Interesting to see what others are doing. I buy my guitar in four days and then later I hope to do my own HID thingie. You deserve some Scooby snacks for that one!
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chok



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PostPosted: Sun May 18, 2008 12:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Hye,
Cool, very good project. I have a same with priority encoder (4532 or TTL similar)...But my english is very average...sorry Embarassed
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TheShaggyDA



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PostPosted: Sun May 18, 2008 7:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Inventor wrote:
Wow, rock on ShaggyDA, that looks awesome! Interesting to see what others are doing. I buy my guitar in four days and then later I hope to do my own HID thingie. You deserve some Scooby snacks for that one!

Thanks Smile

It took me a weekend to put the fretboard together, but that was after toying for a few weeks with a one string proof of concept. (AKA a stick, some toothpicks, some staples, some drawing pins, a paper clip and a bit of wire) Smile Prior to that was 25 years waiting for the final bit of the jigsaw to fall into place for me to start it Smile It was originally going to be a mono controller for my Yamaha CS15 that's collecting dust in the loft, although now I know what I'm doing, I'll probably make a few Smile


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PostPosted: Sun May 18, 2008 3:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

TheShaggyDA wrote:
I'm currently building a guitar synth, got a 4 string proof of concept board working, and I'm shortly going to put it in a real guitar neck.


Hey, cool thing Cool

And welcome aboard!

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nofrets



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PostPosted: Sun May 18, 2008 5:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's fantastic - and almost exactly what I've been pondering. Can't wait to see/hear more about it!
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PostPosted: Mon May 19, 2008 8:19 am    Post subject: Reply with quote  Mark this post and the followings unread

When it's finished I'll be sticking up a few web pages on it, but until then I'll gladly share my scribblings and answer any questions (to the best of my ability) Smile

I would have liked to have built a standalone MIDI controller rather than use the PC, but I'm a better programmer than I am an engineer, and keeping it PC based means I can also code in some extra goodies at a later date, like arpeggiators, one note auto-chords, two hand tapping etc.

I've also written some software for the Ion iED05 USB Drum kit so that it can trigger MIDI on the PC. I need to lean out the code though as it's not polling as fast as I'd like it too, but I might incorporate an extra bunch of piezo pads on the body of the guitar so that I can throw in some percussive effects while I'm playing. One thing at a time though Smile

The wife's out of the country for a month in a couple of weeks, so I can turn the kitchen back into a workshop and stay up all night - with a bit of luck I'll have the basic "mark 1" finished by mid June Smile
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Randy Jones



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PostPosted: Thu Jun 11, 2009 3:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Some students working with Dan Overholt at Aalborg University in Denmark are finishing up a controller in a guitar neck using my capacitive multi-touch sensor idea. For audio interfaces to run the sensor they are using some dirt-cheap USB 2x6 boards made by some Chinese company, then making them into an aggregate audio device on MacOS. See their videos [vimeo.com], and await more information as I am doing. Smile

I started a company, Madrona Labs, to make the controller and other things. It has a website.

I first posted this to a long-dead thread that I think will be hard to find now, so I hope nobody minds the cross-post.
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