Lecture Notes and Papers for how to do common projects in robotics:

Intro to simple sensors

Resistive Sensors and Comparators

Servo Motor Basics

DARC Board User Manual

How to make the DARC Board Parallel Cable Adapter

QRB-1134 Photoreflective Sensor Quickconnect Cable

Making a simple beam break sensor

Modifying Hobby Servo Motors for Continuous Rototation