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The WorkShop




Photogate Trigger Kits, unassembled

SPG1 and SPG2


This kit has been discontinued. See updated options on this page.

Above: Assembled photogate circuit on a breadboard.

Click on any image for a larger view.
Below: The two types of sensor cables.
variable separation photogate cable Interrupter photogate cable

SPG1 cable

(variable width)

SPG2 cable




The Photogate Trigger comes in two versions. Both versions use the same breadboard circuit. However, they have different sensor cables as described below.


Variable-width (SPG1). The matched infrared emitter and detector have separate housings. This allows the two parts to be placed different distances apart, depending on the application. The maximum separation is about a foot (30 cm). If your application requires greater separations, a red laser pointer can be substituted for the infrared LED.


Interrupter (SPG2). The emitter and detector are housed in a single interrupter-style unit. The interrupter, shown to lower right, has a slot of fixed width between the emitter and detector posts. The separation of the posts (5/8" or 1.5 cm) is wide enough for liquid drops and small projectiles to pass.


The kit includes 3 feet of 3-conductor cable to extend the emitter-detector pair to a location away from the breadboard. 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.

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