Here you find some useful information about the sensoring projects I did:

Photointerrupters and rotary encoders

In this series I built an optical rotary encoder that senses the position and also the direction of rotation:

•  photointerrupter basics
• photointerrupter schematic details
• make your own rotary encoder
• make it a quadrature encoder
• code examples for arduino

I did all this  because I needed a simple winding machine.

Temperature sensors

National Semiconductor

Some special issues I stumbled upon when using a LM35 analog temperature sensor connected to an arduino.

Enjoy

heliosoph