Hello Hemanth,

A tutorial on PID controllers is at http://www.eie.polyu.edu.hk/~enkin/hd/PID.pdf

The last three pages of the tutorial describe the difference equations (for discrete implementation in a micro) used to implement P, I and D terms. There is a brief description of how to apply the Ziegler-Nichols tuning method to find "good" values of r the P, I and D gain values.

Ziegler-Nichols is the most popular tuning method used for industrial applications. It does not guarantee optimal response in the controlled variables or the least energy consumed to effect control. It is robust and easily applied in the field without an analytical model of the process.

Control Engineering frequently has articles about PID algorithms, how they work, and sometimes gets into self tuning regulators.

A textbook with more depth is Digital Control authored by Franklin, Powell and Workman.

Good Luck,

Bruce