i'm working on an automatic shuffle machine for regular poker decks.
measuring the height of the stacked deck is prone to errors due to the precision needed, even a slightly bent card would screw everything.
How are you shuffling the cards?
Bending a card doesn't change its weight.
using the weight could be interesting but i would still need a really precise measurement
Not really. You could hack an inexpensive 100 or 200 gram weigh scale and hook it up to an Arduino via an HX711 ADC or use a scale that has RS232 output (which the Arduino can read via a MAX232 or similar).