In article , Craig Lefort wrote:
I am looking for some help in designing a very simple passive measurement
sensor system. Basically, I'd like to have some type of sensor (?) that
would be able to count the number of a specific object in a certain area and
output that number to some display. These objects could just have some
passive element that the sensor could detect, or give off some signal to
detect. For example, lets say there are 10 marbles on a table, 5 green and 5
blue marbles. I want some sensor to be able to tell me the number of green
marbles and the number of blue marbles in a given small area of the table
(i.e. some of the marbles might be out of this given area) and display it
electronically. Could anyone suggest or point me in the direction in the
kind of system I'd need to set up. Should something be attached or embedded
in the marbles that can be detected?

you could make the blue marbles out of steel and the green ones out of copper
so that they'd respond, (differently) to low frequency electro magnetic waves.
but then you'd possibly have troouble gettin the sensor loop right so that a
single loop could count all the marbles...

on the other hand maybe a cheap USB camera and some vision software
could get you the result you want, how hard can it be to program a computer
to count green dots .

Bye.
Jasen