Can I use a visible light or other emitter for the photogate trigger?
The photogate trigger circuit described on this site normally uses a small infrared emitter. You can also use it with the light from a flashlight or red laser pointer. The latter requires precise alignment of the laser beam with the sensing element of the phototransistor. You may be able to make the alignment less critical by diffusing the beam in front of the detector. This may also help if the beam is too intense, making it difficult to adjust the sensitivity of the circuit. Also see item 4 below. One problem with many laser pointers is that the pushbutton is momentary. If you use such a pointer, you need to clamp or tape the button down. There are sources for inexpensive laser pointers with switches that lock in the on position. For example, see this item from Advance Auto Parts.
