My project is a simple system wired to a photo-resistor that’s value is sent to an analog input of the arduino. 5V comes from the arduino into the  breadboard, which is followed by a 5.6K resistor, photoresistor and ground. From there I used Firmata (a feature within Arduino) and Max/MSP to receive the values from the photoresistor and use them for processing.

I used the current value as a Low Frequency Oscillator within max. It determines the frequency at which volume is being modulated on the sound that is leaving Max.

https://drive.google.com/file/d/0B-Zy9oeEXbOwaC0xazZ0TFZFSXM/view?usp=sharing

The video shows that when I cover the photo resistor with my finger the volume is modulated faster, and when i uncover it the modulation is slower.