Whats the difference between an SPG1 and an SPG2 photogate?
The SPG1 is the most flexible of the two versions, because the emitter and detector can be positioned independently of each other. Objects of various sizes can pass through the SPG1 photogate. The SPG2 uses an interrupter as shown to the right. The emitter and detector are fixed in position in a plastic housing. This is convenient for triggering on drops but is limited to objects that can pass through the gate. You can use either type of photogate with the same base trigger circuit.
