Hi.
Great project!
I`m just in a similar project right now 
Ordered a bunch of hardware, but I'm still uncertain how to control it.
using a 550d with ml.
I'm a little bit afraid of frying my arduino if i connect it right to my hotshoe pc sync adapter, but i think these is the way i'm going.
Does somebody know how the pc signal is?
is it high/low or connection/no connection between those two wires...
and is the signal "high" all the time the curtain is open?
hope for good answers