#1
I did a project in physics on how a guitar pickup works.
I thought it would be awesome if I strummed my guitar and it light up a light bulb. Cool, right? I could show it to the class when I present. Well the bulb is 120v, so it obviously couldn't be powered by my guitar. I tried a small LED as well. My questions are:

How many volts does a pickup give?
and
What can I power with that?
or
Is there any way that I can make that signal stronger?
-->Fender Squier Bullet Strat
-->Fender Deluxe Players Strat

-->Dunlop Crybaby 535Q wah
-->Behringer EM600 Echo Machine (piece o' crap)
-->Boss SD-1 Super Overdrive

-->Fender Mustang II
-->RMS GA-10
#2
According to wiki:

For passive pickups its "100 mV rms to over 1 V rms for higher output pickups". I don't really know how accurate that is and hopefully somebody more qualified can answer if that's wrong.

As to what you can power with that, no clue.
Quote by zgr0826
My culture is worthless and absolutely inferior to the almighty Leaf.


Quote by JustRooster
I incurred the wrath of the Association of White Knights. Specifically the Parent's Basement branch of service.
#3
A passive pickup will put out very little power. If you "make it stronger" then it is not really the pickup doing the work, now is it? There are active pickups (rather an active circuit) with 9v batteries but again it is really the battery making the signal stronger.

If you have a really high output passive pup you might be able to light up something but I doubt it will be any spectacle. Something something impedances something something wattages.
Last edited by Will Lane at May 10, 2016,
#4
There is something that can make the signal stronger as a matter of fact, it's called an amplifier.




Sorry I had to. To answer your question, I don't think you are going to get enough power out the pickup by itself to power a bulb, though you might could light up an LED very dimly...

It's a pretty low voltage, VERY low current output. Hence, we plug it into big amplifiers.
I'm just a kickin' and a gougin' in the mud and the blood and the beer.
#5
I bet a good science fair project would be to devise a way of measuring the power, and then explaining why you're not able to light up those lights. Sounds like your class hasn't covered the difference between voltage and power yet.

The short answer is that there's very little power there, and you're not going to light up much of anything with a passive pickup as the only power source. Perhaps there are some super low power LEDs out there that might work, but nothing that you could just plug in and light up in front of the class.

"Is there any way I can make that signal stronger"
That would be called an amplifier :P:
You could make a device that would light up instead of making sound, but I can't think of anything off the shelf that would do it. Maybe someone else knows of something.

I would think that a voltmeter or oscilloscope might give you a decent visual display, and both are likely enough to be found in or around a science classroom. It's not the same as strumming and lighting up a bulb, but it'll add a visual element. The scope would actually be really neat.
#6
Quote by Roc8995
I bet a good science fair project would be to devise a way of measuring the power, and then explaining why you're not able to light up those lights. Sounds like your class hasn't covered the difference between voltage and power yet.

The short answer is that there's very little power there, and you're not going to light up much of anything with a passive pickup as the only power source. Perhaps there are some super low power LEDs out there that might work, but nothing that you could just plug in and light up in front of the class.

"Is there any way I can make that signal stronger"
That would be called an amplifier :P:
You could make a device that would light up instead of making sound, but I can't think of anything off the shelf that would do it. Maybe someone else knows of something.

I would think that a voltmeter or oscilloscope might give you a decent visual display, and both are likely enough to be found in or around a science classroom. It's not the same as strumming and lighting up a bulb, but it'll add a visual element. The scope would actually be really neat.


Well yes, we haven't covered the difference between those two (I am a high school freshman). I thought that there wasn't much that it could power, but I wanted to know if there was anything that wouldn't require much to light up. I guess there's not. I know that you could use the actual amplifier (the part inside of the amp that amplifies the signal, not the whole amp). I just don't have that stuff sitting around.

Is there any other way besides a voltmeter to show that a current is running through the copper coil? There are a lot of knowledgeable people on ultimate guitar, especially in the field of pickups (obviously), so I thought this would be a good place to ask.
-->Fender Squier Bullet Strat
-->Fender Deluxe Players Strat

-->Dunlop Crybaby 535Q wah
-->Behringer EM600 Echo Machine (piece o' crap)
-->Boss SD-1 Super Overdrive

-->Fender Mustang II
-->RMS GA-10
#7
Quote by nate8olson
Well yes, we haven't covered the difference between those two (I am a high school freshman). I thought that there wasn't much that it could power, but I wanted to know if there was anything that wouldn't require much to light up. I guess there's not. I know that you could use the actual amplifier (the part inside of the amp that amplifies the signal, not the whole amp). I just don't have that stuff sitting around.

Is there any other way besides a voltmeter to show that a current is running through the copper coil? There are a lot of knowledgeable people on ultimate guitar, especially in the field of pickups (obviously), so I thought this would be a good place to ask.

Given how small the induced current is, a voltmeter is the most practical way to show it.

However, you could get a 1/4" to 3.5mm jack, plug it into a computer's mic socket, connect the guitar to it and record the raw signal being output.
Quote by Diemon Dave
Don't go ninjerin nobody don't need ninjerin'
#8
I like Roc's suggestion.

The LED is intriguing, because you can take an LED diode, such as those used in stomp boxes, and wire it is series with a K ohm resistance, and a 9v source will light it up brightly. I have this in my home-made bypass loop box. I'm guessing this means it doesn't need either much current or much voltage. What they do need, however, is to be wired up in the right direction. Did you try it connected both ways? I think they are also easy to burn out, but I doubt that a pickup would be powerful enough to do that.
#9
Quote by Tony Done
I like Roc's suggestion.

The LED is intriguing, because you can take an LED diode, such as those used in stomp boxes, and wire it is series with a K ohm resistance, and a 9v source will light it up brightly. I have this in my home-made bypass loop box. I'm guessing this means it doesn't need either much current or much voltage. What they do need, however, is to be wired up in the right direction. Did you try it connected both ways? I think they are also easy to burn out, but I doubt that a pickup would be powerful enough to do that.


Output from a pickup is AC, not DC.

From what I can tell, induced current is around 650nA and average output of a hot pickup is around 450mV, for an output power of .4uW (These numbers may be wildly inaccurate, there aren't a lot of sources)

Even if rectified with no loss I don't think that will light up any LED made.
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
#10
OK, if it's AC, why can I get a positive or negative voltage reading on my multimeter when I do a "flick" test, depending on which way I connect the pickup? Even it is AC, since it is a diode, why wouldn't it drive an LED through half of its cycle?

I think you're right that it isn't enough to power a pickup though.
#11
Quote by Tony Done
I like Roc's suggestion.

The LED is intriguing, because you can take an LED diode, such as those used in stomp boxes, and wire it is series with a K ohm resistance, and a 9v source will light it up brightly. I have this in my home-made bypass loop box. I'm guessing this means it doesn't need either much current or much voltage. What they do need, however, is to be wired up in the right direction. Did you try it connected both ways? I think they are also easy to burn out, but I doubt that a pickup would be powerful enough to do that.

I have tried both ways on a couple different LEDs. Also, I only have one pickup connected, not the wires from the output jack of the guitar. I guess it's just not strong enough.
-->Fender Squier Bullet Strat
-->Fender Deluxe Players Strat

-->Dunlop Crybaby 535Q wah
-->Behringer EM600 Echo Machine (piece o' crap)
-->Boss SD-1 Super Overdrive

-->Fender Mustang II
-->RMS GA-10
#12
Let's say you get 1VRMS out of a 15K ohm high output pickup. That's only 0.07 milliamps. Divide that by 2 since the LED will rectify it. I don't think 0.035 milliamps is going to light an LED.
#13
LEDs, like any other diode, need a certain voltage to turn on. It depends on the specific LED but values from 1.5 to 3v are common. Most guitar pickups won't manage that.

The limiting factor here is not the pickup, but the string. Even if you could somehow convert 100% of the string's energy into electrical energy, I doubt there would be enough to put on a light show.
Last edited by sashki at May 10, 2016,
#14
No, the transfer to the pickup output is the limiting factor. There's plenty of energy in the string.

Think about it this way - it's trivial to power an LED (or even a whole bunch of them) with a hand crank device. Even if we afford the strings a tiny fraction of the energy transferred, there's still plenty of power there in the form of motion. Physical movement takes a lot more power than we tend to think about.

The major loss occurs instead in the transfer from the string vibration to the inducted current. There's a huge energy loss there, many orders of magnitude beyond what is lost between your hand/pick and the string. Induction is very inefficient and anyway pickups aren't designed for efficiency. They'd be terribly noisy and unpleasant if they were.

If you were very interested in doing the math yourself, you could compare the energies a) created by the hand/pick, b) imparted to the string and c) the output of the pickup. I think you will find that there's plenty in the string (especially if you consider all six!) and far, far less at the pickup output.

Hard mode:
https://books.google.com/books?id=I0uMgKmcSrgC&pg=PA43&lpg=PA43 (examples 1.7 and 1.8.3)

Easy mode: relate the power required to create a sound of a certain volume from an acoustic guitar to the amount of power required to run a small battery charger or solar-powered LED.
#15
Passive pickups are measured in mV, or millivolts. These are pretty tiny. There might be really tiny LEDs that work, but nothing like an actual bulb. Maybe if you wire a few hundred guitarists in series.
Dave @ Seymour Duncan
#16
Quote by Mincer
Passive pickups are measured in mV, or millivolts. These are pretty tiny. There might be really tiny LEDs that work, but nothing like an actual bulb. Maybe if you wire a few hundred guitarists in series.


Many pickups average about 450mV, or about half a volt, which is sufficient for some led's. The problem isn't the voltage, it's the amperage.

You would need to wire them in parallel.

“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
#17
If the pickup is 100milivolts ac, it would only take 1200 pickups wired in series to make 120 volt ac. Is that right? I wonder how many watts a pickup produces? Just as a science experiment though, you would need the lowest wattage light that you could find. Then who says you have to use a guitar string? You could use a flywheel, a tuning fork or a high powered magnet. In fact, even if the lightbulb idea doesnt work out it can be fun to place a magnet over a pickup and get sound out the amplifier with no vibrating strings. Also it might be possible to find a passive speaker sensitive enough to make noise with out an amp. -just hooked directly to the pickup. You could also wind your own pickup that is designed for voltage. You also might need a bridge rectifier if you want to use dc bulbs or speakers. It's possible to make a radio that is powered entirely by the antenna, so i think your idea is possible. You only have to show that the pickup makes electricity. How much energy you have to force into that pickup is not important haha. Like, use a magneto off of an old tractor. Just because it takes a tractor to generate the power to make a pickup light up a lightbulb doesnt mean it cant be done. Ha the 100 watt 3 amp amps we use to play takes a nuclear generator or a niagra falls on the other end.
Last edited by geo-rage at May 13, 2016,
#18
Quote by Tony Done
OK, if it's AC, why can I get a positive or negative voltage reading on my multimeter when I do a "flick" test, depending on which way I connect the pickup? Even it is AC, since it is a diode, why wouldn't it drive an LED through half of its cycle?

I think you're right that it isn't enough to power a pickup though.

I mean it's absolutely not in doubt that it's AC, since induction can only ever produce alternating currents (the voltage is proportional to the rate of change of flux, and it's impossible for the flux to change continuously in one direction). As for powering the LED through half the cycle, maybe, I don't know

One major source of energy loss here is because a pickup is part of a very poor magnetic circuit. You've got a permanent magnet, and that's got flux lines (flux lines aren't a real thing, but they model the behaviour of actual flux) coming out of one end of the magnet, going in a loop and back in the other end of the magnet. The string is in the path of those flux lines, so when it moves they shift about some, but for the most part the flux is passing through air, which has very low permeability* (equivalent to low conductivity*, or high resistivity* in an electrical circuit, just with magnets) so your flux is spread out and weak and the string only interacts with a small part of it.

A good magnetic circuit, such as a transformer, has a core guiding the flux round it, traditionally made of iron since iron has a high permeability. So a coil in a good magnetic circuit looks like this. Trouble is, there's no space for a string. That's alright, put a gap in it and put the string in that gap; the circuit is significantly worse than the one without a gap in it, but significantly better than the basic pickup which is just a plain old magnet under the string with a coil round it. Obviously, there are a lot of other considerations here, for example that the string needs space to vibrate. Even so, pickups using a better magnetic circuit do exist, and indeed have been used for a long time (I imagine they were necessitated by limitations on the number of winds you could put on a pickup coil back in the day, so they had to seek better efficiency elsewhere); this is from a 1930s Rickenbacker, where the horseshoes, rather than the polepieces are actually the magnets, and the polepieces guide the flux through the strings:


Nice, right? I imagine that'll remain entirely theoretical as far as OP's science project is concerned, but maybe you can use something resembling a core to improve the efficiency of the magnetic circuit. Mostly I just wanted to flex my magnet knowledge. I'll get back to you if I figure out the actual power with which a string vibrates.

*These are properties of materials; permeance, conductance, and resistance are all properties of objects made from those materials. A resistor has resistance, the stuff it's made from has resistivity.
#20
I think a cool thing to show on a science fair is how a speaker when wired as a microphone is actually a microphone.

http://www.instructables.com/id/turn-ANY-speaker-into-a-microphone-in-just-2-easy-/

Some studios use this exact method for kick microphones.

http://www.soundonsound.com/sos/nov14/articles/qanda-1114-04.htm
#21
I know the point is to power a lightnulb with a guitar and ive always wanted to do that too, but how about this thing? It seems 300millivolts is too low for a light bulb but im not giving up on that just yet. Also the internet seemed to think ,ha, that a solar calculater might be low enough voltage to work but the amps might not be there.

https://www.amazon.co.uk/gp/aw/d/B00842JL8I?fp=1&pc_redir=T1