The optical guitar pickup.

[moeburn]

I got a little 10k LDR and a bottle cap.  Cut the bottlecap so it was thin enough to fit under my guitar strings.  Drilled a hole in it, put the LDR under it, hooked it up to my headphone amp.  I positioned the pickup under my string so that the shadow of the string was right on top of the hole (i'm using sunlight at this point).  

The sound was absolutely phenomenal, sustain is extremely long, there is no noise whatsoever.

Now that I know it works, I'm gonna design a proper prototype (covered to avoid light pollution, LEDs instead of sunlight).  

However, I need some advice.  Where should I position this pickup on my guitar?  It is going to be covered, don't forget, so it will eliminate a portion of the strings.  If its at the bridge, you won't be able to palm mute, at least not very well.

[vanhansen]

Middle or neck at first but you should be able to get it work well in the bridge if it's covered.  This sounds like a very cool idea.  I'm interested in how your progress progresses.  

[moeburn]

Middle or neck at first but you should be able to get it work well in the bridge if it's covered.  

The problem with middle and neck is that the strings like to vibrate alot futher, complicates things.  Don't forget this has to cover the strings, so you can't pick the strings wherever i put it.

Which is why this would work so much better on a bass.

[vanhansen]

Oh, ok, I see.  I thought by "covered" you meant the pickup would be covered but you're talking about covering the strings like on a vintage P-Bass that has the cover over the strings and pickups.  Well, what's the diameter of the LDR?  If it's no wider than a normal pickup pole piece, it may still pick it up ok.  It's worth trying anyway.

[moeburn]

Well, what's the diameter of the LDR?  If it's no wider than a normal pickup pole piece, it may still pick it up ok.  It's worth trying anyway.

My LDR is the exact same diameter as the pickup pole, but the hole i drilled for it is much smaller, only 1/32".  I'll try it.

[Thomas P.]

I belive I read something about this in an article about the NAMM and they placed it close to the bridge.

Regards,
tomboy

[smashinator]

Is there a reason you're making an optical pickup, or is it just for the sheer joy of mad science?

Either way, cool idea.  Personally, I tend to pick behind the neck pickup, so I'd want it mounted pretty far forward.

[moeburn]

Is there a reason you're making an optical pickup, or is it just for the sheer joy of mad science?

Mad science, of course

After a bit more playing around, this is sounding alot easier than I thought it would be.  Each string is equally bright and loud with the same single pickup.  Every sound you can make comes through just as expected, including scraping the strings, different picking techniques, chiming, etc.  Except of course, palm muting.

Since it is getting dark here, I tried using a ceiling light instead of the sunlight.  Lots of 60hz noise, and having three bulbs at slightly different angles makes for a pretty cool effect.

[R.G.]

Did you perhaps use a phototransistor instead of an LDR?

Most LDRs are too slow to respond to 60Hz changes in light intensity from bulbs, let alone string vibration frequencies. In fact, getting an LDR fast enough for phaser use is some times tough.

I wonder what happens when someone takes your picture with a flash camera?

[aaronkessman]

im not sure i understand how you're getting a signal out to the amp. do you have a signal generator which the LDR controls? if so, hahah - instant tuning changes! weee!

if not, then how? also, this could all happen in a little enclosed box which is smaller than a SC pup but fits around the strings. wouldnt be much of a problem in that respect.

[Marcos - Munky]

Sorry, but I didn't understood. How a optical pickup will work, if a LDR or a phototransistor can pick only lights, not sounds or vibrations?

[Thomas P.]

Sure it only picks up light which alters the resistance of the LDR. While having a maybe constant voltage applied the current through the device will alter with the frequenzy of the string.

Regards,
tomboy

[moeburn]

Michael Faraday (Captain Capacitor) discovered that whenever a magnetic field (pickup magnet) is moved or changed (string induces change in magnet) in a conductor (pickup coil), a current is produced.  This is how your guitar strings can actually generate sound without simply being a variable resistor.  They generate about 10-200mV.

The LDR, although a tiny puny magnetic field, is a magnetic field.  Works just the same as an electret microphone.

Unfortunately, my LDR isn't quite that strong.  I had to use my preamp at full volume, my TS at full volume (minus distortion), and my amp at full volume, to get a normal volume of the guitar.  This is probably because the difference between shadow and sunlight isn't strong enough.  

Once I get it inside a dark enclosure, with a bright LED as the source, it will be much louder.  But you will still probably have to have an active guitar with batteries in it.  

I just thought of another neat advantage though - nylon guitar strings on an electric.  Imagine that!

[tommy.genes]

Optical pickups are already being sold, although only for bass at the moment.

http://www.lightwave-systems.com

-- T. G. --

[moeburn]

Optical pickups are already being sold, although only for bass at the moment.

http://www.lightwave-systems.com

-- T. G. --

Yeah, thats why I said this would work so much better on a bass

But its so much cooler when you get it working before they do.

[Narcosynthesis]

having a quick look at the lightwave system, they use infra red light, which seems like a better idea than a normal led, as with normal light, you are almost always going to get extraneous light influencing the pickup, ie a slightly different output/sound between a well lit room and a dingy bar, using infra red leds and ldrs would hopefully solve that

David

[moeburn]

having a quick look at the lightwave system, they use infra red light, which seems like a better idea than a normal led, as with normal light, you are almost always going to get extraneous light influencing the pickup, ie a slightly different output/sound between a well lit room and a dingy bar, using infra red leds and ldrs would hopefully solve that

David

Either way, its in an enclosed case, so light interference won't be a problem at all.  But there is near IR and far IR pollution everywhere anyway.  I think they used IR LEDs because they are much more efficient and wear out batteries slower, which is a good idea.  At least, I think they're more efficient.  My only IR exploded when i hooked it up without a resistor.

[corbs]

I just thought of another neat advantage though - nylon guitar strings on an electric.  Imagine that!

ooh you might get some cool diffraction weirdness too  

[Thomas P.]

The LDR, although a tiny puny magnetic field, is a magnetic field.  Works just the same as an electret microphone.

I don't see where you got a magnetic field with a LDR :?:

Regards,
tomboy

[petemoore]

There was something like this advertised in Guitar Player Mag IIRC, was a light sensor/light pickup with a sizable structure just in front of the bridge over the strings. It stated 'works with any type strings even nylon strings'...