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Optical guitar pickup


moeburn
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I'm interested in trying to design an optical guitar pickup, pretty much an LED and a photocell that sense the movement of the string and convert it to an audio signal.  Unfortunately, I can't even get a simple demo to work with an LED and photocell, mostly because I have no idea how to amplify it.  Any ideas?

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Hi moeburn

I recently did some design work on an absolute angle encoder, arising out of that I looked at 'other' ways of achieving a solution.  One of these ways was to use a cmos strip or CCD sensor, there are a few companies, mainly in California which supply them and which may be a solution to your problem, I'll take a look at my notes and come back later.

Best of Luck

Ed

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Hi

this is the sort of thing I was thinking of, a Fairchild 2048x1 pixel sensor.  Whilst many are designed for use with scientific instruments, I'm sure that you'll find others which are much cheaper and which could be used either staggered or in line to cover the full distance beneath the strings and to include pitch bending

Best of Luck

Ed

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Hi Alun

basically, none at all and the magnetic pickup is well proven and cheap. Using the type of thing I suggested would probably get people involved in DSP and the higher realms of mathematics.

But the original question was about designing an optical means of achieving the same thing - probably its most important outcome was a learning exercise and, don't know about anyone else but that's one of the main reasons why I enjoy this forum.

All the Best

Ed

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Ed, the vibration of the string is the same in all directions from the core for the string frequency, which is where the magnetic pickup excels. In a visual system, you would need to take into account that when the string is plucked, it will have a sideways movement, which can be different each time depending upon who is plucking, how hard, and  possibly different from time to time. This deos not effect a magnetic pick up. Perhaps this is where your problem lies. It seems like you would also have different points of defraction/refraction of the LED where the light hits the vibrating string.
Hope it is food for thought.

MP

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Hi MP

I'm aware of the differences between and advantages of mag pickup, if you check back the posts, what I've done is provide one possible solution to moeburns' original question and hopefully given food for thought.

Perhaps this is where your problem lies


? my problem?

On your point about diffraction and vertical movement, it's a good one and the cmos/ccd sensor in conjunction with DSP could provide a solution by measuring the rate of change of shadowing since the sensor is a nice mixture of analogue and digital technology.  Digital in terms of position and analogue in that an analogue voltage is produced in each bin.

All the Best

Ed
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  • 3 weeks later...

I have desinged a few, there is one particularly effective yet simple way to achive, the amplification you desire, but the circuit is a bit more complex. 1 instead of using a solar cell use a IR phototransistor, your sensor and pre-amplification is solved with this one little device. Second you will need to chain 6 of these photo transistors, into a 6 channel mixer, with a 50-60hz notch filter. You will hear a horrible buzzing sound if you don't use the notch filter. With a 9v batter you can acheve awesome gain, with no distortion. The talk of using CCD's are just rediculus. Most people don't realize that the string modulates the light's waveform, that is what causes the modulation in the sensor. Angle smangles they don't matter since the light will be modulated, and no matter what path it takes to the photosensor it will still be modulated. I have built this pickup for my experimental guitar, thinking I had a patentable Idea, but by the time I was old enought to file for a patent I found out that idea has been out there for 28 years before my implementation of it. However for experimenting and fun that is the way you would go about building a optical pickup, not rocket science, but just plain old good sound.

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Guest Alun

I understand; if the string casts a shadow over a sensor when it's in one position then it moves it allows the light to pass in another, and it's vibrating the light falling on th sensor will be pulse frequency modulated.

Edit:
This wouldn't be of much help any way because there's more information present than just the frequency, this method neglects the amplitude. You'd have to use another method in conjunction with this to provide data about the amplitude.

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