Band of photoresistors

Hello,

I want to connect 10 or 20 photoresistors in series and then connect the whole setup to Arduino so i can see how many of them are on the light and how many are on the dark. I want to do this reading output voltage on an analog pin.

Can you tell me how can i make such a setup?

I don't know if it is possible.

Is it with daylight ? or a light that is always the same brightness ?

Do you want to use LDR ? If you have 10 of them in the dark, the total resistor value could be too high.

um no.

you have to measure each sensor independently, you'd need a lot of analog inputs, the only thing i can think of using is a multiplexing ic, you feed the data in, then command the chip to switch on any of the channels from your sensors feed it into the arduino all into 1 input

You need an "analog multiplexer" chip (or three): http://www.ebay.com/sch/i.html?_nkw=analog+multiplexer

Your problem with that many photo resistor's in seriese is that one photo resistor will have very little change in the over all resistance. So you won't be able to differentiate between one being illuminated well and all of them slightly.

The other way to say this is, when you're reading only at the ends of a chain of Rs in series, you're reading the equivalent resistance for the entire chain,

Req = R1 + R2 + R3 + ... + R20

and there is no way to tell what the individual R values are. Eg, they all can be 0 ohms except for one of them, or they all can have the same resistance, &etc.

Simple arithmetic. The sum tells you nothing about the values being added up.