Case #96: Nick Has an Illuminating Flashback

January 08, 2007

Photography enthusiast Nick Pagazani was hindered by the range and fixed location of his camera's flash. Since his camera has no connector for an external flash, he needed a light-activated slave trigger to fire a remote strobe. It had to ignore the pre-flashes used for red-eye correction and fire only on the main flash. His solution: Use a microcontroller to count pulses from a phototransistor and trigger the strobe at a switch-selectable count. Brighten up your shadowy background with this flashy accessory.

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"Slave Strobe"
Amt Part Description Allied Part #
1 PIC12F629 I/P microcontroller 383-0287
2 0.1uF capacitor 613-0513
2 1/4W 1 k Ohm resistor 832-0537
1 1/4W 4.7 k Ohm resistor 296-4769
3 1/4W 10 k Ohm resistor 832-0530
1 1/4W 1 M Ohm resistor 648-0204
1 2N2222 (or other) general-purpose transistor 248-1004
2 SPST toggle switch 683-0085
1 NTE5457 SCR (see schematic for alternate version) 935-6236
Additional parts required
1 NTE3120 (or similar) Photo Transistor
1 3V Lithium Battery and holder
Nuts and washers for the toggle switches
Kaiser Flash Shoe Adapter, available at
Photoflash Strobe
PIC development kit & software to program the PIC: K8048 (kit), Vm111 (assembled), available at - requires RS232 port and cable. USB versions are also available.

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