PID_v1.cpp

/**********************************************************************************************
 * Arduino PID Library - Version 1.2.1
 * by Brett Beauregard <br3ttb@gmail.com> brettbeauregard.com
 *
 * This Library is licensed under the MIT License
 **********************************************************************************************/

#if ARDUINO >= 100
#include "Arduino.h"
#else
#include "WProgram.h"
#endif

#include <PID_v1.h>

/*Constructor (...)*********************************************************
 *    The parameters specified here are those for for which we can't set up
 *    reliable defaults, so we need to have the user set them.
 ***************************************************************************/
PID::PID(float Input, float Output, float Setpoint,
         float Kp, float Ki, float Kd, int POn, int ControllerDirection)
{
   PID::Input = Input;
   PID::Output = Output;
   PID::Setpoint = Setpoint;
   inAuto = false;

   PID::SetOutputLimits(0, 255); // default output limit corresponds to
                                 // the arduino pwm limits

   SampleTime = 100; // default Controller Sample Time is 0.1 seconds

   PID::SetControllerDirection(ControllerDirection);
   PID::SetTunings(Kp, Ki, Kd, POn);

   lastTime = millis() - SampleTime;
}

/*Constructor (...)*********************************************************
 *    To allow backwards compatability for v1.1, or for people that just want
 *    to use Proportional on Error without explicitly saying so
 ***************************************************************************/

PID::PID(float Input, float Output, float Setpoint,
         float Kp, float Ki, float Kd, int ControllerDirection)
    : PID::PID(Input, Output, Setpoint, Kp, Ki, Kd, P_ON_E, ControllerDirection)
{
}

/* Compute() **********************************************************************
 *     This, as they say, is where the magic happens.  this function should be called
 *   every time "void loop()" executes.  the function will decide for itself whether a new
 *   pid Output needs to be computed.  returns true when the output is computed,
 *   false when nothing has been done.
 **********************************************************************************/
bool PID::Compute()
{
   if (!inAuto)
      return false;
   unsigned long now = millis();
   unsigned long timeChange = (now - lastTime);
   if (timeChange >= SampleTime)
   {
      /*Compute all the working error variables*/
      float input = Input;
      float error = Setpoint - input;
      float dInput = (input - lastInput);
      outputSum += (ki * error);

      /*Add Proportional on Measurement, if P_ON_M is specified*/
      if (!pOnE)
         outputSum -= kp * dInput;

      if (outputSum > outMax)
         outputSum = outMax;
      else if (outputSum < outMin)
         outputSum = outMin;

      /*Add Proportional on Error, if P_ON_E is specified*/
      float output;
      if (pOnE)
         output = kp * error;
      else
         output = 0;

      /*Compute Rest of PID Output*/
      output += outputSum - kd * dInput;

      if (output > outMax)
         output = outMax;
      else if (output < outMin)
         output = outMin;
      Output = output;

      /*Remember some variables for next time*/
      lastInput = input;
      lastTime = now;
      return true;
   }
   else
      return false;
}

/* SetTunings(...)*************************************************************
 * This function allows the controller's dynamic performance to be adjusted.
 * it's called automatically from the constructor, but tunings can also
 * be adjusted on the fly during normal operation
 ******************************************************************************/
void PID::SetTunings(float Kp, float Ki, float Kd, int POn)
{
   if (Kp < 0 || Ki < 0 || Kd < 0)
      return;

   pOn = POn;
   pOnE = POn == P_ON_E;

   dispKp = Kp;
   dispKi = Ki;
   dispKd = Kd;

   float SampleTimeInSec = ((float)SampleTime) / 1000;
   kp = Kp;
   ki = Ki * SampleTimeInSec;
   kd = Kd / SampleTimeInSec;

   if (controllerDirection == REVERSE)
   {
      kp = (0 - kp);
      ki = (0 - ki);
      kd = (0 - kd);
   }
}

/* SetTunings(...)*************************************************************
 * Set Tunings using the last-rembered POn setting
 ******************************************************************************/
void PID::SetTunings(float Kp, float Ki, float Kd)
{
   SetTunings(Kp, Ki, Kd, pOn);
}

/* SetSampleTime(...) *********************************************************
 * sets the period, in Milliseconds, at which the calculation is performed
 ******************************************************************************/
void PID::SetSampleTime(int NewSampleTime)
{
   if (NewSampleTime > 0)
   {
      float ratio = (float)NewSampleTime / (float)SampleTime;
      ki *= ratio;
      kd /= ratio;
      SampleTime = (unsigned long)NewSampleTime;
   }
}

/* SetOutputLimits(...)****************************************************
 *     This function will be used far more often than SetInputLimits.  while
 *  the input to the controller will generally be in the 0-1023 range (which is
 *  the default already,)  the output will be a little different.  maybe they'll
 *  be doing a time window and will need 0-8000 or something.  or maybe they'll
 *  want to clamp it from 0-125.  who knows.  at any rate, that can all be done
 *  here.
 **************************************************************************/
void PID::SetOutputLimits(float Min, float Max)
{
   if (Min >= Max)
      return;
   outMin = Min;
   outMax = Max;

   if (inAuto)
   {
      if (Output > outMax)
         Output = outMax;
      else if (Output < outMin)
         Output = outMin;

      if (outputSum > outMax)
         outputSum = outMax;
      else if (outputSum < outMin)
         outputSum = outMin;
   }
}

/* SetMode(...)****************************************************************
 * Allows the controller Mode to be set to manual (0) or Automatic (non-zero)
 * when the transition from manual to auto occurs, the controller is
 * automatically initialized
 ******************************************************************************/
void PID::SetMode(int Mode)
{
   bool newAuto = (Mode == AUTOMATIC);
   if (newAuto && !inAuto)
   { /*we just went from manual to auto*/
      PID::Initialize();
   }
   inAuto = newAuto;
}

/* Initialize()****************************************************************
 *	does all the things that need to happen to ensure a bumpless transfer
 *  from manual to automatic mode.
 ******************************************************************************/
void PID::Initialize()
{
   outputSum = Output;
   lastInput = Input;
   if (outputSum > outMax)
      outputSum = outMax;
   else if (outputSum < outMin)
      outputSum = outMin;
}

/* SetControllerDirection(...)*************************************************
 * The PID will either be connected to a DIRECT acting process (+Output leads
 * to +Input) or a REVERSE acting process(+Output leads to -Input.)  we need to
 * know which one, because otherwise we may increase the output when we should
 * be decreasing.  This is called from the constructor.
 ******************************************************************************/
void PID::SetControllerDirection(int Direction)
{
   if (inAuto && Direction != controllerDirection)
   {
      kp = (0 - kp);
      ki = (0 - ki);
      kd = (0 - kd);
   }
   controllerDirection = Direction;
}

/* Status Funcions*************************************************************
 * Just because you set the Kp=-1 doesn't mean it actually happened.  these
 * functions query the internal state of the PID.  they're here for display
 * purposes.  this are the functions the PID Front-end uses for example
 ******************************************************************************/
float PID::GetKp() { return dispKp; }
float PID::GetKi() { return dispKi; }
float PID::GetKd() { return dispKd; }
int PID::GetMode() { return inAuto ? AUTOMATIC : MANUAL; }
int PID::GetDirection() { return controllerDirection; }