I've spent my summer mostly working at the institute of molecular genetics, and whatever time there was left in between that and other typically summery exploits was spent with Parsley, our tesla coil. Since people asked; here is a bit more on my favorite toy (and probably the most murderous - and arguably the prettiest - thing I've ever built).
We started building her (it's obviously a she, look at those curves!) over a year ago. I've met someone at the hackerspace who happens to be crazy in exactly the same direction as I am - work went slowly, we spent most of the last summer on the driver and power electronics (she's a double-resonant solid state coil using two IGBTs and a driver with current feedback from the primary coil, you can find more technical info on her here
). We ran first tests and measurements in autumn, and just when I finished her primary coil and both driver and power circuitry - on the same day, even - I got hospitalized for the holidays. We resumed work on her shortly after I got out, and after a minor setback (induction on the feedback coil fried half of the driver) and some tuning we got her to work eventually in early spring. We went about it cautiously, not more than one third of full power (she's fed through an old soviet variac so we can regulate current input) - but already she produced 20-50 cm sparks.
This summer, we finished her electronics, active cooling for the IGBTs and took her outside - now her arcs reach the floor on about 80-100VAC input. My friend made her a new controller, connected to her via fiber-optic cable - and most importantly, capable of MIDI input.
So these days, she's an almost finished singing tesla coil. Here's a video of her singing
:] I ordered a keyboard for her which should arrive next week. If anyone in Prague knows how to play keyboard and wants to give her a try, let me know!
People's reactions to her never cease to fascinate me. They range from skeptical "isn't it completely useless? why have you built it?" and almost derogatory, through frightened "won't it kill you and everyone else around you?" all the way to enthusiastic appreciation - enthusiasm, sometimes, from entirely unexpected people.
But most importantly, I love that damn thing to bits. It's a dream come true.