Check if a dispenser actually "dispensed" an item

Hi,

I’m trying to build something similar to this dispenser https://www.instructables.com/id/Smart-Contact-Dispenser/, but trying to make it commercial. As people will pay money, I’d like to be extra sure that the item being bought is actually delivered. I’m using a stepper motor to remove the bottom item in the stack into a tray, but I’d like an additional layer of certainty. Any ideas what else I could use? I was thinking maybe a brightness sensor…

Thanks,
George

Would not, once an item has been dispensed, the weight of the items lessen?

I was thinking maybe a brightness sensor..

What are you intending to sense the brightness of?

Idahowalker:
Would not, once an item has been dispensed, the weight of the items lessen?

They're not that heavy, I'm thinking 10-15 grams per piece

PaulS:
What are you intending to sense the brightness of?

The piece is going to fall in a predetermined location, so I assumed the …. you're right, it's a pretty long shot.

It's assumed the 'item' will have some packaging. Does the package have any special properties - metallic, color, shape, etc?

george_bulimar:
The piece is going to fall in a predetermined location, so I assumed the …. you're right, it's a pretty long shot.

The piece might break a light beam?

dougp:
It's assumed the 'item' will have some packaging. Does the package have any special properties - metallic, color, shape, etc?

Not really, it will be a 1010 cm1cm coffee coaster wrapped in plastic

PaulS:
The piece might break a light beam?

This might work. Put an led on one side and see if the light beam breaks. Thanks

You might consider an AND gate type of system to detect if the product has been dispensed. Meaning one way can go wrong or has its detractions but two ways and that both ways have to 'say' yes should be more reliable.