I need a sensor setup to detect if something passes through an opening after I click a button

I am making a compartment that holds up to 7 different vitamin pills separately. Each of the 7 slots has a small doorway that allows the pills to exit from the slots (after I click the button) and then each of the 7 pills falls/slides along a trail to end up in the middle (basically a way to distribute different vitamin pills to make it less time consuming to consume).
What kind of sensor or setup would I need to make that happen? I'm guessing 7 different sensors are attached to the 7 slots on the machine.
But after something passes through, the doorway closes automatically after detecting that one pill/object has existed the gate.