Making a Guitar Tuner - Need help getting voltage from guitar

[tareqx2]

I am making a digital guitar tuner for one of my class projects. The only problem i have run into is getting actual voltage output from my guitar.
How would i hook it up? I have it plugged into a mono jack, do i need to send in a voltage to receive a voltage? I'm not too knowledgable on this.
Thanks for any help

[ianmgull]

Get a voltage out of a guitar? Pluck the string.  Keep in mind depending on the pickups, there may be well under a volt output.

[R.G.]

Good call Ian.

The output from a guitar is NOT a sine wave, and varies from about 0.1 to 1.0V peak when the string has just been struck. To make a good tuner, you'll need to amplify the signal up so your frequency detection works down at least to 10mV. You will also need to eliminate the string harmonics from the fundamental by some filtering. Probably you'll want to make the filtering adaptive, unless you want to limit your tuning to only the two octaves of the open strings in standard tuning.

Making tuning lights blink the right way when a signal generator is supplying the signal is easy. Digging the fundamental out of a guitar signal is a challenging analog design problem. Going direct to digital from the guitar signal only makes this into a challenging digital filtering problem along with an modestly challenging analog design problem, because the A-D generally has some issues with the small signal level too.

[head_spaz]

Has there ever been an auto-tuner ...  something like using a nulling bridge to actuate a servo that twists the tuners?
That would be cool! But the prototype builder would need a string sponsor. Can you imagine all the strings they'd snap?

[Naz Nomad]

Has there ever been an auto-tuner ...  something like using a nulling bridge to actuate a servo that twists the tuners?
That would be cool!

http://www.gibson.com/robotguitar/

[jacobyjd]

Has there ever been an auto-tuner ...  something like using a nulling bridge to actuate a servo that twists the tuners?
That would be cool!

http://www.gibson.com/robotguitar/

There's really only one reason why I'd never be interested in one of those.

Have you ever strapped one on? Feels like it weighs 20lb! 

[Naz Nomad]

Have you ever strapped one on? Feels like it weighs 20lb! 

The same reason my LP is on permanent loan to my bro-in-law.

[cobra94]

Hey Naz what other guitars do you have...and do you have a sister? 

[tareqx2]

Good call Ian.

The output from a guitar is NOT a sine wave, and varies from about 0.1 to 1.0V peak when the string has just been struck. To make a good tuner, you'll need to amplify the signal up so your frequency detection works down at least to 10mV. You will also need to eliminate the string harmonics from the fundamental by some filtering. Probably you'll want to make the filtering adaptive, unless you want to limit your tuning to only the two octaves of the open strings in standard tuning.

Making tuning lights blink the right way when a signal generator is supplying the signal is easy. Digging the fundamental out of a guitar signal is a challenging analog design problem. Going direct to digital from the guitar signal only makes this into a challenging digital filtering problem along with an modestly challenging analog design problem, because the A-D generally has some issues with the small signal level too.

the guitar only outputs a voltage, and not a sine wave? So to make my tuner (I will tackle the filtering later because it doesn't necessarily have to be an accurate tuner at all), I will have to amplify the voltage output obviously with an opamp, and then run that through a voltage to frequency IC? What i have so far is a board that i programmed to input a square or sine wave and convert that to the frequency by timing the falling edges. I tested it out with a frequency generator and it is working. Just need to interface it with the guitar and i'm set. Any tips to where i can go from here? Thanks for your response

[MetalGuy]

There are already couple of similar projects around in the net. I built one of them based on PIC16F84 and the only thing I didn't like it was too slow in detecting which string is which at least for my taste. An old KORG GT-3 is musch faster. I was wondering if i could make it faster simply by using higher frequency oscillator.
This is the schematic:

http://www.electro-tech-online.com/attachments/electronic-projects-design-ideas-reviews/8833d1153678251-modified-guitar-tuner-circuit-porzio-circuit-mod.gif

If you're interested I can send you the code and stuff because it doesn't seem to be available online anymore.

[puretube]

What R.G. said:
a square or sine from a "generator" is easy to detect...

From a guitar-signal, you want it to become of a constant amplitude for a (little) while;

You can do that with a sort of "compressor", or a kind of "limiter" or other "AGC";

but: these can or will introduce even more higher harmonics of the fundamental pitch
that you are bound to detect;


especially when the strings already output a ("trebly") waveform which crosses "through zero"
more often than the actual fundamental to be detected, would do;

since about 70 years, people have been trying to find out the best way...

If time allows, some examles will show up here.

[MoltenVoltage]

put your guitar signal through an oscilloscope and look what is happening

depending how hard you pluck the string and which string you pluck, you will get VERY different voltages

you need to detect the peaks then calculate the time between peaks, then do it again a couple more times to check whether they all agree, and figure out what to do when the don't agree

you'll most likely need to boost the signal on its way to the uC, but will need to be careful that it doesn't distort and add harmonics like others have mentioned

as mentioned, you've picked a pretty tricky project.  you might want to buy a digital tuner and take it apart to see what kind of filtering is used, as I suspect they filter everything they can below the low E and above the high E (assuming you only want standard tuning)