Jose;

You may not need PID at all..

If you just want to do AC power control, try simply programming a follower.
Let's say you have a target setpoint.  Then make a second variable of the
same type that goes to the output.  Alllow a timer to increment or decrement
the following variable on a periodic basis.  You can then adjust the rate of
change of the follower.  This will allow a somewhat sloppy feedback control,
and is much easier to program.  You will have implemented an I term only
controller.

Chris Eddy
Pioneer Microsystems, Inc.

DIAZ SUSANIBAR wrote:

> Thank you for reading this message. i am student of electronic, and
> I have a hard task. I need to control the output of a
> variac(kind of autotransformer), I think to do this measure the
> output voltage, and then with this do a PID control into PIC, but I dont
> know how to do a pid control into PIC. then the pic set a circuit which
> active or desactive a dc motor for change the voltage of the variac.
> I am really sad and fear because i dont know how to do this
> sorry for all. thank you very much.
>                                          SINCERELY
>                                           JOSE DIAZ