Return it. Seems "defective" to me.
Where did you buy it?

did you assembled it yourself?

No, the link implie that I do not know, but want to help.

which is highly problematic as it makes smoothing pretty much useless

But, wouldn't you actually need to smooth the signal to get an accurate reading?

Time to wait for the experts  

wait, I found this:

Having worked with pH probes in a refinery, I can tell you that they always have to have external very very high impedance buffering and DC gain amplifiers, with manual drift adjustments. Drift is a constant battle, as well as cleaning of the probe on a regular basis and calibrating with a buffering solution. Also the pH scale is a logarithmic scale and the 10 bit A/D converter in the Arduino is probably not a good match if reasonable accuracy is needed. And last, any analog measurement that can have a valid negative value cannot be measured by an Arduino, as it is strictly a 0 to some positive voltage value (depending on reference used), no negative values allowed.

Ok to play around with, but if it's at all a serious application I think the Arduino needs lots of external circuitry help for pH measurement.

Lefty

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1270669602/12

I think this is your problem. But you should post your schematic here, so when the experts come, they will be able to help you right away.

http://hackaday.com/2009/09/01/arduino-ph-meter/

http://lh5.ggpht.com/_CjTtOo4QsAQ/SpxZLVArCKI/AAAAAAAAAL0/7gO3MwHGcnw/s800/pHduino_v02.02_scheme.png

maybe this will help you.

maybe your solution Ph is between two values and this is why it doesn't stop oscilliating.  We can get the same phenomenon with all electronic measurement devices.

and btw, the different "samples" in your picture, it was all the same and the Arduino detected it as different?

My first experience was also a pain.
I got better the second time (UM, I mean...day)
But still crappy looking with lots of wires and potentional shorts. (still trying to learn how to make jumper wire)

its software.

We sure could improve power consumption  

I'd have to use a digital pin anyway to detect the external sensor, so I don't really see the point in using an extra component?  

Me either. I like doing simple things complicate.  :

Until the real expert come back and help you...

1-Walmart will probably blow up
2-????? (I don't know about rectifier)
3-Plug the Heat pump with his respective power suply, separate from the Arduino.

4-I do believe the arduino Pins only take DC or it would blow up(I like that word) (the reason why you want to convert AC to DC) From my very tiny knowledge base, you should probably use an external device (detector) wired to the Arduino to register if the pump is On or OFF.

And btw, if your heat pump require AC, use AC, not DC.

I don't know how your heat pump is or work, but if I was trying to do that I would try to detect the Heat exchange using a electronic Heat sensor or something similar, but it's probably not the best way to do that and might be unreliable as you will need to do some qualibration...maybe using one sensor to detect the ambiant temperature and the other one beside your heat pump.

even horizontally you will probably get data. (since there is always some sort of acceleration or unbalanced mouvement)
as far as I know, the only way to get a Y value of 0 is a free fall  ;D

Not sure about this, but accelerometer values are not X, Y, Z coordination. They are accelerations and vectors, but they can be used to find an angle.

Gyroscope is rotation.

Not sure, like I said. Maybe a multi-axis can do it.

Im currently reading the link...

Nunchuck is 3 axis alright.

Read this:

http://arduino.cc/en/Reference/Map

It would run faster, be less stable, make more heat and break.

I don't know if it's possible (if it is, then it's hard and you will need multiples arduino)
You could glue a magnet under each chess pieces. To know if a case is vacant or used, you could use a few Hall effect sensor positioned on top of your Led array.
I don't think it's important to filter the surrounding magnetic field.
Then, maybe it's possible with trigonometry to actually detect where the field is stronger (with the multiples Hall effect sensor) and get a somewhat clear position, just use the same magnet model/type for each pieces.

With RFID you could assign the correct chesspiece an ID so the arduino know what are the pieces. If you can write in the sketch some basic rules of Chess (aka, game grid, start position and chess pieces) Maybe it could actually follow the mouvements of each pieces from the start to the end of the game.

This is just an idea, all theory...keep in mind that I'm a complete n00b and I don't own any Arduino.  

or Just use push buttons, more simple.

Thats is freaking awesome.