What do I need to make my own electronic Butterfly in a jar?

Here it is : https://www.youtube.com/watch?v=-sSbKb8EU2U
I found it at 18$, and I considered it's expensive and I should do it myself.
I could use a simple jar, acoustic guitar string ,but do I need a uC or an oscillator? What kind of piezo sensor?

This is very nice... thanks for sharing. By the word "uC" do you mean a microcontroller? Although I am not sure as to what you should really use for this project of yours... I am pretty sure you don't need a microcontroller for this project. The guy in the video did mention the use of motion sensors, you can explore that option.

I suspect the electronic butterfly uses "muscle wire" to move the wings. Jameco stocks this.

http://www.jameco.com/webapp/wcs/stores/servl...ew?rf=1&history=9lpieb3p|freeText~muscle+wire^search_type~jamecoall^prodPage~15^page~SEARCH+NAV&sort_field=Price+(Descending)&position=1&refine=1&langId=-1&catalogId=10001&storeId=10001

To power the wire, as you say, an oscillator is needed having a triangular waveform to slowly move the wire. I think two oscillators having different frequencies can drive the wire driver stage so that the movement appears somewhat natural and is not exactly periodic. And, as you also said, a uC could be used for an even more natural movement.

A uC _would_ make it easier to simulate random behavior. But, if I were to do it with discretes, I would use a low frequency sawtooth osc connected to a sample-and-hold that is sampled whenever the sensor detected tapping. That sampled voltage would then be tied to the Voltage Control input on a 555 timer (and the timer would be triggered by the sound sensor circuit). The 555 would be in a one-shot configuration and would drive the motor that agitates the butterfly. Perhaps another lo-frequency sawtooth osc (set to a different frequency than the first sawtooth) fed through a voltage follower to provide the supply voltage of the motor -- if the 555 is triggered when the second sawtooth wave is at a low voltage, the butterfly's movements would be more sluggish and if triggered at a higher point on the ramp, then the butterfly would be more vigorous.

Something like that.

@davi_d: we actually bought one of these for a gift, and of course, played with it before we gave it away. It appeared that it was as simple as a motor twisting a length of fishing line. The butterfly is attached to the other end of the fishing line. By twisting the line back and forth, the butterfly was made to appear to flutter around in a vain attempt to free it self from the jar.

I don't think there was any muscle wire involved -- and in fact, I doubt if the muscle wire would respond fast enough to produce the kind of movement we saw (which was actually far better, and more realistic, than what is shown in the video that Daiana linked to).

More like this:
http://youtu.be/9DyTx0hvmqE

Steve, the motor and fishing line is an ingenious way to do this. Was the eccentric movement provided by an electronic circuit or by some mechanical mechanism?

I don't know -- I didn't take it apart -- I just played with it a bit before sending it on.