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Flash Trigger MkI

May 3rd, 2008 by tsKegel

As I previously mentioned, I have been working on a trigger for my flash gun (a Canon 580ex). The reason I wanted a flash trigger was because it is very difficult to take a picture at the exact time an event occurs, and the exposure time is always going to be limited by the shutter speed, having a long exposure with a small aperture, means that the photo exposure is essentially determined by the length of the flash, which in many cases is faster than you can achieve with a flash attached to a camera conventionally due to sync speed limitations between flash and camera. I have been using the arduino platform to build the flash trigger.

I had some very simple requirements for my trigger:

The execution had to be simple
It had to be expandable
It had to be flexible
It had to work, and work well

The end result was a trigger with a piezo sensor to set it off, an optoisolator to protect the arduino from any voltage spikes that might occur from the flash gun, a potentiometer (variable resistor) to add a delay after the sensing and before the triggering and a cut pc sync cable to connect to the flash.

Along with this was some simple code to be loaded on to the arduino:

int piezopin = 5; int flashpin = 2; int potdelaypin = 0; int threshold = 100;

void setup(){ pinMode(flashpin, OUTPUT); }

void loop(){ int piezoval = 0; piezoval = analogRead(piezopin);

int potdelay = 0; potdelay = analogRead(potdelaypin);

if(piezoval >= threshold){ delay(potdelay); digitalWrite(flashpin, HIGH); delay(10); digitalWrite(flashpin, LOW); } else { digitalWrite(flashpin, LOW); } }

In case it is not obvious, all the code does is read the piezo value, check it against a set tolerance and, if it is above the tolerance, trigger the flash after a delay set by the value of the potentiometer.

I decided to test the system by smashing an ice cube above the sensor, in the hopes that I might get a picture of the ice shattering and flying away from the hammer. The results of this were great, but to begin with the flash was firing too quickly, and the ice did not have a chance to be thrown away from the hammer the pictures ended up looking like the hammer was just resting on some broken ice. I cranked up the potentiometer and the results were fantastic, the delay worked perfectly and allowed the pieces to fly away from the hammer.

Another shot I wanted to try was dropping a cup of water and catching the spray of the water as it was cast off. Again, it didn’t work until I introduced a delay, but once I did, it looked amazing, the flash made the water sparkle in a really beautiful way.