Light sensor switch

[cameracut]

Hello, this my first thread so I hope its clear enough for you!

I am in the process of making my first Mini-Sumo 'bot and is in need of a circuit that would allow it to tell the difference of light and dark colored floors. It would be nice if it could be as minimal as possible and have the ability to, when it is dark, have full resistance and when it is light, it will have no resistance. Kinda like if you were to have a normal switch with purely on and off but it will sense the color.

Thanks for any help!

[sonictj]

these sensors are designed for this purpose http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/qti/List/0/SortField/4/ProductID/100/Default.aspx

they aredesigned for an rc timeout, but you can attach a 10k resistor between W and R to create an analog sensor.  to eliminate confusion do to poor labeling on parallax's part I'll give you the pin out for an analog setup.  B = ground, R= signal, W = +5V.

Another option is the pololu qtr line they come in either analog or digital (rc timeout).

http://www.pololu.com/catalog/product/958