Hackaday Links: April 16, 2011

Induction cook top provides power too

We’re familiar with induction cook tops but we never thought to power a microcontroller with one. [Thanks Hadez]

Ping-Pong Uranium

We’ve been big fans of the chain reaction demonstration using ping-pong balls and mouse traps ever since we saw [Mr. Wizard] do it back in the day. If you don’t know what we’re talking about, check out this demonstration that is analogous of a fission reaction. [Thanks nateL]

Phone tripod enclosure

If you’re interested in using your smart phone for some photography, [Mike] has a nice wood and elastic mount for an iPhone which you might try yourself.

Bicycle snow tires

Admittedly we’re a bit late on this one. But keep it in mind for next year: you can use some zip ties for added traction on your bike when it snows. [Thanks Rob]

Now you can BE mario

A little Kinect script lets this gentleman play Super Mario Bros. with his body. Now you can have all the fun that goes along with being a pixellated character stuck in a two-dimensional environment (plus, there are shrooms). [Thanks Das_Coach via Slashdot]

Oscilloscope Piano Tuning 101

fft on scope

[Todd Harrison] recently wrote in to tip us off on his submission to the Tektronix oscilloscope contest – using a scope to tune a piano. In his video he demonstrates how a Fast Fourier Transform can be used to determine the fundamental frequency of the note being played. This is a quick and easy way to determine if that key is in tune, and if not, how far off it is from the desired frequency and in which direction.

He goes on to explain that a scope can only be used as a starting reference point since “mathematically correct” tuning on a piano doesn’t sound right to the human ear. It turns out that when struck, the stretched wires in the piano behave less than ideally. In the case of a piano, the overtones (the other peaks shown on the scope higher in frequency than the fundamental) are actually slightly sharper (higher in frequency) than the expected harmonic whole-number multiple of the fundamental frequency.  As a result, the frequency ranges of each octave must be “stretched” in order to accommodate this and sound correct when multiple notes are played together across octaves.

Typically, only the A4 key is actually tuned to its correct frequency of 440Hz and all of the other keys are manually tuned off of this baseline. The amount of necessary stretch applied to each octave increases as you get further away from this initial reference point in either direction and is unique to each and every individual instrument – thus there is no universal device capable of perfect tuning. Although [Todd] admits that he won’t attempt to tune the entire piano himself using this technique, he finds it a convenient way to keep the most heavily played center sections of the piano closer to true between professional tunings.

If you have any interesting or unique uses for your Techtronix scope, you can enter the contest here. Just don’t forget to tip us off too!  Thanks [Todd]!