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Xy55
02-09-2007, 02:21 AM
Hello!

I'm currently building a touchsensing guitar that would do away with strings.

I came across this LED touch sensor design and was intrigued:
http://cefn.com/curiosity/?p=206

I was wondering if someone can direct me to some parts and information that I would need to look into to build something like this? I need to map out the first 3 frets of all 6 strings (18notes) for my prototype, but I would eventually like to have all 144 notes mapped out. I don't have to use leds or anything, buttons will also work for me. I just needed an interface that would register when the user pushs a certain note on the guitar. Ideally the signal can go to something like a NI BNC-2120 and we would do some signal processing there and then have an analog out that would go to the amp.

BASIC Stamps seem relatively cheap and easy to use. So this is definitely a likely option for me. I guess the problem would be how to mount the sensors ona BASIC stamp that would fit on the neck of the guitar, or maybe just attaching sensors on the neck and have that wired to a stamp that's just sitting on a table or something. Please let me know what you guys think and if there is any more information you need. Currently sensor options include:

Buttons (.20/per)
FSR ($35 bucks for a 24" strip)
LEDs (haven't done too much research, but that link above uses leds)

Thanks! feel free to email me too - xiao85yu@hotmail.com (mailto:xiao85yu@hotmail.com)

AIman
02-09-2007, 02:24 AM
There is a Parallax page that I would suggest you look at.

http://www.parallax.com/html_pages/products/componentshop/sensors.asp

In particular two items - Flexiforce Sensor Demo Kit (http://www.parallax.com/detail.asp?product_id=30056)and QT113-D Touch Sensor (http://www.parallax.com/detail.asp?product_id=604-00038)

Either of these would work for what you want.

Xy55
02-09-2007, 02:33 AM
AIman, yeah i've looked at those, but the QT113-D is just too expensive for a student project and I would need 18 of those sensors just to finish my prototype and eventually 144 for my entire design. They were priced at 8$ per :-p

Forgot to ask something earlier, but how do you design a receptor that can take up to 144 inputs on a stamp? For the time being, I just have to worry about the 18 input one, but even that, are there built in inputs on the board itself or would I have to look for something else? Basically all I need is something that sends a high when pushed, and low when it's not pushed.

Roger Pierson
02-09-2007, 03:09 AM
Could you use a photo diode to signal when someone's finger has covered the correct spot on the guitar?

www.newark.com/jsp/Semiconductors+&+Prototyping/Discretes/VISHAY+SILICONIX/BP104/displayProduct.jsp?sku=14M4504 (http://www.newark.com/jsp/Semiconductors+&+Prototyping/Discretes/VISHAY+SILICONIX/BP104/displayProduct.jsp?sku=14M4504)

Also in general, places like Newark and Mouser have IC's and common components cheaper than Parallax.

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Roger Pierson
Senior Electronics Technicain
DTI Assoicates

Mike Green
02-09-2007, 03:23 AM
The easiest and cheapest way to accept large numbers of digital inputs is with something like the 74HC165 parallel to serial 8-bit shift register. These can be cascaded and provide 8 logic inputs per IC. If you're going to use switch closures, you can scan a 12 x 12 matrix or 18 x 8 matrix. The big problem you run into quickly is the limited variable storage for processing.

The most important question is what kind of fingering do you want to be able to do? Switch closures are only on/off and they take a bit of room for each one. Some kind of "touch screen" like sensor may be able to respond only to one finger at a time. The LED touch sensor sounds neat, but would take some work. It seems to be sensitive to ambient light, but you ought to be able to experiment with it using a Stamp.