Here's the deal: I've got my English finals coming up this Friday, the 6th. With no budget, I am supposed to make something that represents a very important time in my life. I want to use my cello as a base to represent my musical background, but I want to include my Arduino in there to show how my my E.E. has gotten me on my own. I've got a small 1 metre LED strip that uses common anode RGB LEDs and I was wondering if I could use the steel strings on my cello and my fingers to change the color of the LEDs based on my hand position on the cello using burdon voltages and resistance. Should I be using a special nicrome wire, or can I just use some bog-standard copper from an Ethernet wire? I can scrounge up my old grounding strap if I can find it, and that would be a good cathode. If at all possible, I was also wondering if I can run this whole thing using a 12 volt bench-top PSU. My board is the Uno SMD edition, and I can probably use the Analog In pins and some transistors, or I can have the LED strip seperate from my Arduino and just have it drive some flashy LEDs to go in the F-Holes.
PLEASE NOTE I WILL NOT REPLY AFTER 22.00 PACIFIC STANDARD TIME AND IT WILL BE TOO LATE FOR HELP
I have a cello also, I don't see how steel wrapped catgut will offer much change in resistance as you move your fingers up & down the string.
Might have better luck with just a mic and an op amp to make a changing DC level based on frequency, do analog read and use that for LED control.
I've actually just measured the voltage:
A - 2.5 Ohms
D - 1.3 Ohms
G - 1.4 Ohms
C - 0.5 Ohms
That's practically noise. That's just about useless for me right now. Thanks for the tip. I'll consider it when I actually get around to playing this thing. It's been just about 4 years since I last played every day.
Those are resistances, not voltages. What did you measure?
CrossRoads:
I have a cello also, I don't see how steel wrapped catgut will offer much change in resistance as you move your fingers up & down the string.
Might have better luck with just a mic and an op amp to make a changing DC level based on frequency, do analog read and use that for LED control.
CrossRoads,
Can you explain how you would go about doing this? Would I use one of those clip-on tuner contact mics? I, for now, would just like to play with using instruments as Arduino inputs. I have never been a musician (unless you count the two years I played percussion in school), so I'm not sure where to begin on that side of things. Would the arduino be able to detect a frequency?
Thanks
Ferreri:
English finals.....
Strange type of project for 'English' finals.
make something that represents a very important time in my life..... I want to use my cello as a base to represent my musical background .....I have never been a musician (unless you count the two years I played percussion in school)
Hmmm. I guess your "musical background" must be listening to music. 
Does this really count as "a very important time in my life"?
PLEASE NOTE I WILL NOT REPLY AFTER 22.00 PACIFIC STANDARD TIME AND IT WILL BE TOO LATE FOR HELP
Even if it's too late, not replying to people who try to help is a bit rude. (Many of us are in different time zones, and would have to mess around on the web to find out what time it is where you are.)
And expecting to complete a project like this in one day is fairly optimistic. Barely time to accumulate the necessary components, if you can get them locally.
OldSteve,
You seem to have lumped my reply with the original poster, who may or may not be someone who finds music to be very important in their life.
I do enjoy listening to music, but that's not why I'm here.
I want to explore the idea of using instruments as inputs for the Arduino.
Ferreri:
OldSteve,
You seem to have lumped my reply with the original poster, who may or may not be someone who finds music to be very important in their life.
I do enjoy listening to music, but that's not why I'm here.
I want to explore the idea of using instruments as inputs for the Arduino.
Yes, I do seem to have done that, don't I? 
Sorry about that - I didn't realise that you'd replied to an old thread from a couple of years ago, and thought you were the OP.
It always gets confusing when someone replies to an old thread with their own questions. Really, you should have started your own, and linked back to the relevant post in the old one, to avoid any confusion.
CrossRoads' method, "mic and an op amp to make a changing DC level based on frequency", would actually give a changing DC level based on amplitude, as far as I can see, not on frequency. He must have had a particular frequency to voltage circuit in mind.
I made a sound-level switch the other day, using a condenser microphone and a single transistor amplifier stage, followed by a peak detector/comparator, but it responds to sound amplitude, not frequency.
If you only had a specific frequency in mind, you could use a bandpass filter to isolate the frequency of interest and amplify it, but otherwise harmonics would get in the way as well.
If harmonics weren't a problem, you could use a comparator to 'square up' the audio signal, then time the distance between rising or falling edges to determine frequency and go from there. Or if you want to dig into analogue electronics a bit deeper, Google "frequency to voltage converter".
There are guitar-like electric pickups for cellos.
Cheaper: Using a mic and pre-amp to get a +/-1V signal, amplify that a little to get it to 2.5V +/- 2V and read with analogRead.
I believe there is FFT routine you can run to pick out dominant frequency. Every cello sound has levels of other frequencies also, that's what make the pleasant sound vs just sounding like a simple sine wave. You can probably low-pass filter the sound also to cut out the higher frequency harmonics.
CrossRoads:
I believe there is FFT routine you can run to pick out dominant frequency.
This sounds interesting. I just Googled "dominant frequency FFT" and got a bunch of results. While I still have a mic and preamp set up, I might have a bit of a play as well.