That is
I need 60 analog input pins.
I need to follow a shadow so I thought in a line of light sensors
the line can be covered with about 60 sensors. Knowing the sensors position I will know
where the shadow is ....
how can I connect about 60 light sensors to an arduino board ?
any idea of a better way to do that ?
If you need to follow a shadow, is it moving on consecutive points / sensors, or is it jumping all over the place ?
If it follows a fixed path, you don't need to read all sensors every time, you just need to know whether it moves forward or backward (or not at all).
That can save you a lot of time.
Also read a sensor of which you know it is not in your shadow.
Use that value for calibration, to compensate changes in the lighting because you depend on that.
You use two multiplexers, 74HC4051. One is used to ground the "rows" of your 8 by 8 matrix of sensors, while the other connects a given matrix "column" to the ADC input (which has a pull-up to Vcc). If the sensors are naturally diodes, such as photo-transistors, you simply have the emitters to rows and collectors to columns. If they are bidirectional, such as LDRs, you have a diode in series with each, cathode to "row", anode through LDR to "column".
Of course, another way to do this is to have one LDR or photo-transistor at the end of a black tube, mounted on a servo arm which you use to "scan" for the shadow.