Position sensors

  • Thread starter xtr
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  • #1
xtr
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Hi I'm new to the forum and I have a question about position sensors.

I am looking to obtain a position sensor, to be used in the construction of a musical instrument. The sensor will not only sense the presence of my hand in front of it, but will also determine the position of my hand relative to it as a function of time. This data must then be digitized to give a list of position-time values, for input into a software program. The sensor's range should around 1 to 1.5 meters.

My first guess would be an infrared sensor for this task, but I have no experience with the technology. I also have a number of other sensors available to me like Hall-effect sensors and light dependant resistors.

If anyone has any suggestions or tips on what type or model of sensor is best for this job, I would greatly appreciate the advice. If there is another forum that would be more sutiable for this question then please let me know. Thank you.
 

Answers and Replies

  • #2
dlgoff
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You might want to check out theremins. Do a google search. Here a Theremin Kit.
Regards
 
  • #3
Integral
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From my knowledge of position sensors I would say that your demands are extreme. You will not find a simple sensor, infrared or otherwise, which can produce the output you need. You are seeking a location in 3 dimensions, this is not the usual task for a simple sensor.

It would seem to me that what you require would be better described as a vision system... Good luck.
 
  • #4
berkeman
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dlgoff said:
You might want to check out theremins. Do a google search. Here a Theremin Kit.
Regards
The link didn't work for me, dlgoff. Is it right?

For xtr -- I think you have at least two options, depending on how much freedom of movement you want. The easiest and cheapest way would be to use 3 linear motion sensors with rods that move back and forth. The rods each go through a ball that has a wide range of rotational freedom. The 3 balls are located below, in front of, and to the side of the position where the musician's hand will start. The 3 rods are connected together with a flexible arrangement right where the hand will start. The musician holds some sort of handle where the 3 rods are joined, and as s/he moves their hand in 3-D, the rods glide back and forth in their anchor balls (the balls spin as necessary). You digitize the linear rod motions, and convert those into the x,y,z position of the hand. The 3 anchor balls don't even need to be totally orthogonal -- you could arrange them in a triangle in front of the musician, for instance, and still be able to calculate the 3-D position of the hand from the linear motions of the 3 rods.

If it is too intrusive to the musician to have to hold something during the hand motions, then I agree that some sort of video imaging should be used. You'll need at least two 2-D cameras to get the 3-D position of the hand, and some sort of "target" marking on a glove or something will help the image processing that you'll need to do to calculate the 3-D hand position. Kind of like the little white balls that are glued onto athletes when they do the video recordings to help look at their motions to improve in their sports.

Let us know what you figure out! -Mike-
 
  • #5
Danger
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I remember a couple of decades back being quite taken with an interactive hologram that I couldn't begin to afford. It was a full-size '57 Chevy dashboard. There was a 'curtain' of laser emitter/detector pairs (hidden IR units) in front of the radio. When you poked one of the non-existent 'buttons' with your finger, the real radio hidden inside would change channels. Maybe something like that could work in your application.
 
  • #6
es
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Although it doesn't give position directly, how about an accelerometer on a glove. It could be used to produce an effect similar to what you describe, and it's cheap and easy to use. Accelerometer that measure in three dimensions in a package exist:
http://www.freescale.com/files/sensors/doc/fact_sheet/MMA7260QFS.pdf [Broken]
 
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  • #7
Cliff_J
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This sounds a lot like a commercially available device, one that changes musical tones based on how you move your hand in front of the box. If you would be able to purchase one and modify it that would save a lot of development time and you could test the range of their sensors.

Searching can yield good results, here MIT built their own laser range finder to determine hand position.

http://web.media.mit.edu/~strickon/publications/2000_06_ICMC_Surfaces.pdf [Broken]
 
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  • #8
dlgoff
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berkeman said:
The link didn't work for me, dlgoff. Is it right?
It works for me using Firefox. Try this.
 
  • #9
dlgoff
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Cliff_J said:
This sounds a lot like a commercially available device, one that changes musical tones based on how you move your hand in front of the box.
This is the way a theremin works. It uses changes of capacitance by the hands to produce tones.
 

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