The HiViz.com WorkShop
Light-Activated Trigger Kit, unassembled
This trigger operates the reverse of our photogate kits. The output of the light-activated trigger is switched on when light shines on the detector. A laser pointer works particularly well as a light source, since the phototransistor is sensitive to visible light and has a narrow angle of view. You can also use this circuit to trigger a slave flash in response to the discharge of a master flash. The circuit is powered with a 9-V battery or AC/DC adapter (not included).
Cords to connect the breadboard circuit to a flash unit or camera are not included.
In order to trigger a flash unit, see this page for flash cable kit options.
The kit includes 3 feet of 2-conductor cable that can be used to extend the phototransistor away from the breadboard.
An electronic delay unit may be used with the LAT to achieve timing synchronization.