The concept is to take a 'long' exposure photograph, 4 seconds say, in a (very) dark room (a bathroom in our case). You end up with a completely black picture, right ? If you burst a flash (about a millisecond for a standard flash) then you get a picture made of 4 seconds of 'dark' and one millisecond of 'light'. Are you still with me ?
The trick is to burst the flash at the right moment so that the millisecond of light you get illuminates an interesting scene. A popping balloon for example...
This project uses the sound an exploding balloon makes to trigger a flash.
- a DSLR camera (Canon 450D) + tripod.
- an arduino duelaminove + 9v battery.
- a sound sensor (from www.flamingoeda.com). Or better yet (if you don't read japanese): http://stores.ebay.com/FunRobo/_i.html?_nkw=Arduino+Sound+Sensor+Module&submit=Search
- a relay module (on ebay search for 'relay module arduino', sort by price, pay about 5$ for it).
- a cheap flash (paid 10$ for this one).
- a (convenient) sensor shield + cables.
Step 1: Put it together.
The sound sensor returns a 0-1024 value, the relay can be controlled by a digital pin.
I cracked open the flash, removed the shoe and soldered a couple of wires instead.
Some will probably argue that a relay is too slow. Well it turns out it isn't...
To be fair I, too, thought it would be too slow so I have tried and used an opto- isolator. It burned (as well as my atmega328, :-( ) during my first try. The voltage in the shoe of this *very* cheap flash is probably too high for my opto-isolators.
As I have no idea what kind of voltage I am dealing with here (I just know it hurts if I put my fingers !), I took the easy route and used a relay. It works, so... problem solved !