Extra Credit was just to see what people could come up with.
For those interested, I have been fiddling with boost converters recently. The photo is the voltage across an inductor being charged and discharged by a square waveform, into a Schottky diode and a 100uF cap - the circuit acting as a DC-DC boost converter. I am not sure what causes the ringing, and the output is not efficient - cannot get much current out of it. Probably poor selection of choke value, too much choke internal resistance.
I was using a PIC to generate a PWM waveform, connected to two Pots so I could dynamically vary the duty cycle and period. Also connected a variable voltage supply to the input to the choke.
I took other photos too, some showing no ringing - good square waves, others ringing like a bell.
Cheers,
-- Dan