I made a prototype with an arduino uno. It works like a charm. I made some extra code so when I press the 2 button it triggers two photos.

I had some truble when I was testing the new avrusb programmer. I did not work. I made a simple test setup with the Fade example that you can find in the Arduino IDE.

At last I found what was wrong. I use a power regulator on my breadboard to give the Attiny 3.3v. The breadboard is wrong or the power regulator is wrong because the negativ sid connects to the positive side of the breadboard and the positive sid connects to the negative side.

In the image I swiched + to - and vice versa, and it worked.