So, I already have an Arduino and some sensors. Now I want to buy a LEGO EV3, cause I love Legos and it look freaking cool. But is also freaking expensive, and have a limited number of sensors. Can I make the generic arduino sensors work with Lego? If not, can I make the Arduino read the sensors and them output it to the lego?
There are no Arduino sensors: Arduinos can read all manner of sensors, sometimes with appropriate voltage adjustments, but they're not Arduino products.
But whether or not an EV3 can read ordinary everyday sensors is a question you should ask on a Lego forum I'dsay.