Coffee machine waste basket sensor

[bitwelder]

I have a fully automatic coffee machine, one of the those where you supply coffee beans and water, and it makes an espresso at the press of a button.
Generally after about 3 coffee 'pucks' it turns on the 'waste-basket full' alert LED.
I was wondering, what technology could have they used to detect the condition?
The basket is a front-sliding coffee-brown plastic tray, and it doesn't seem to have a load cell to weight it.
Or does it just count the pucks dropped after last tray opening? (never tried to open and close without emptying it)

[Rerouter]

to cut costs i would have to say counting, the only other way may be an IR photo detector inside the cavity somewhere, so as an object is close enough it illuminates the light,

[Ian.M]

Generally after about 3 coffee 'pucks' it turns on the 'waste-basket full' alert LED.

You say 'about'.  Does it actually vary or are you simply qualifying the number due to your own uncertain memory?

Assuming it does different styles of coffee, I would expect it to meter the beans in some way.  It therefore will have a reasonable estimate of the volume of spent grounds per cup.
As long as the consequences of a waste bin overflow are not catastrophic, a simple accounting strategy will be a lot cheaper than sensors.  Some printer manufacturers use the same strategy and the consequences of a waste ink/toner overflow are far far more unpleasant than some spilt coffee grounds!

[bitwelder]

You say 'about'.  Does it actually vary or are you simply qualifying the number due to your own uncertain memory?

Due to my own random access memory. Lately I always see 3 coffee pucks but I think to remember I've seen 4 at least once.

Assuming it does different styles of coffee, I would expect it to meter the beans in some way.  It therefore will have a reasonable estimate of the volume of spent grounds per cup.

Indeed, it must be doing some measuring based on the used coffee. I now tried to fill the waste bin with a small bag of dried beans and a box of tea bags and in neither case the machine detected the 'bin full' status (although the volume occupied was even twice of that used by 3 coffee pucks).
Thanks!