To capture images of bullets “interacting” with various objects, photographic hacker Tyler Gerritsen created an impressive chronograph rig, able to measure the speed of a bullet launched from a rifle at 1000 meters per second. While the concept of measuring time from one sensor to another isn’t new, implementation at this speed required some interesting tricks.
To accomplish this feat, Gerritsen designed his own sensor array using photodiodes in a reverse-biased setup, and even calibrated the clock speed of the Arduino Uno for control in order to account for any variation. Finally, the time between triggering a flash and light actually appearing had to be compensated for in the code, a different value for each type of equipment.
[original story: Arduino Blog]