If you haven’t seen it, here is the original post about the Smart Optical Slave Flash Trigger (SOSFT) prototype built on an Arduino platform. Since I need to free up the Arduino Duemilanove board for other purposes and want to test the trigger in more practical situations, I decided to build it on a small perfboard I found in RadioShack.

Here is the final result.

Smart Optical Slave Trigger

The changes from the original design are minimal. ATMEGA168 is used as the micro controller. I simply programmed the Arduino bootloader and the trigger hex code on the Duemilanove then plugged the chip in the socket on the circuit board. The power supply circuit is added (LM7805C and two capacitors) to supply the 5 volts needed. The unit is powered by a 9 volt battery. To make it easy to connect and disconnect a flash, I used a 3-pin TTL socket I took off a Nikon AS-E900 on the board and the AS-E900 on the flash.

The following is the schematic.

I haven’t found a box yet to put it in but it is robust enough to allow some further testing. The sensitivity is adequate for typical indoor applications. It is surprising since I didn’t use any amplifier. I did see a potential issue. Since the code doesn’t examine the validity of the pulses it detects, the trigger can misfire when the distance from the camera or the commander unit is too far away. The reason is that the detected pulses may not all be above the pre-set threshold. Using the high sensitivity mode helps to extend the distance.

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