Dragonfly synchronization
Synchronization is particularly useful for capturing objects that are in motion. If the cameras are synchronized, you know that images of the scene were taken at the same time. This is important for 3D reconstruction. If the cameras are not synchronized textures will not match up and the reconstructed object will not look very good.
[edit] Why build your own synch unit?
If all of the dragonfly cameras are on the same firewire bus, they synchronize themselves. However, it is often impractical to put many dragonfly cameras on the bus because the bandwidth of the bus is not sufficient to capture large frames at a high frame rate. Point grey used to sell a hardware solution to synchronize firewire cameras that are on separate buses. This product has since been discontinued in favour of a software solution. However, the software solution only works under windows.
[edit] How did we do it?
If you short the ground pin and the IO2 pin on the dragonfly camera (I suggest reading the dragonfly technical reference before you do this) while they are in trigger mode, the camera captures an image. Therefore if all the cameras are in trigger mode you can performed synchronized capturing by shorting the two pins on each of the cameras at the same time. We used a quad-channel opto-isolator made by OSRAM Opto Semiconductors (part no: ILQ615-2) available from http://www.rsaustralia.com (part no: 110208) to achieve this. The opto-isolator isolates each of the cameras, effectively putting them each on a separate circuit. An MSP430 provides the single signal into the opto-isolator telling it when to trigger the cameras.
Ross Smith designed the PCB that the MSP430 is mounted on, he also wrote the code that runs on the MSP430.
I am proud to be able to say that (under Ross' guidance) I soldered all the components to the board. And I think it is my finest effort to date :)
