Expose integral for user-space anti-windup access

PID_v1.cpp

@@ -182,6 +182,20 @@ void PID::SetMode(int Mode)
     inAuto = newAuto;
 }
 
+/* GetIntegral(...)*************************************************************
+ * Get Integral term for user access to anti-windup schemes
+ ******************************************************************************/
+double PID::GetIntegral(){
+    return outputSum; 
+}
+
+/* SetIntegral(...)*************************************************************
+ * Set Integral term for user access to anti-windup schemes
+ ******************************************************************************/
+void PID::SetIntegral(double Integral){
+    outputSum = Integral; 
+}
+
 /* Initialize()****************************************************************
  *	does all the things that need to happen to ensure a bumpless transfer
  *  from manual to automatic mode.

PID_v1.h

@@ -50,6 +50,7 @@ class PID
 										  //   once it is set in the constructor.
     void SetSampleTime(int);              // * sets the frequency, in Milliseconds, with which 
                                           //   the PID calculation is performed.  default is 100
+    void SetIntegral(double);                // * sets the internal Integral term, in output units  
 
 
 
@@ -59,6 +60,7 @@ class PID
 	double GetKd();						  // where it's important to know what is actually 
 	int GetMode();						  //  inside the PID.
 	int GetDirection();					  //
+	double GetIntegral();					  //
 
   private:
 	void Initialize();

examples/PID_SimulatedHeater/PID_SimulatedHeater.ino

@@ -0,0 +1,108 @@
+/********************************************************
+   PID Basic simulated heater Example
+   Reading analog input 0 to control analog PWM output 3
+ ********************************************************/
+//  This simulates a 20W heater block driven by the PID
+//  Vary the setpoint with the Pot, and watch the heater drive the temperature up
+//
+//  Simulation at https://wokwi.com/projects/358122536159671297
+//
+//  Based on
+//  Wokwi https://wokwi.com/projects/357374218559137793
+//  Wokwi https://wokwi.com/projects/356437164264235009
+
+#include <PID_v1.h> // https://github.com/br3ttb/Arduino-PID-Library
+
+//Define Variables we'll be connecting to
+double Setpoint, Input, Output;
+
+//Specify the links and initial tuning parameters
+double Kp = 17, Ki = 0.3, Kd = 2; // works reasonably with sim heater block 
+//double Kp = 255, Ki = .0, Kd = 0; // works reasonably with sim heater block 
+//double Kp = 2, Ki = 5, Kd = 1; // commonly used defaults
+PID myPID(&Input, &Output, &Setpoint, Kp, Ki, Kd, P_ON_E, DIRECT);
+
+const int PWM_PIN = 3;  // UNO PWM pin
+const int INPUT_PIN = -1; // Analog pin for Input (set <0 for simulation)
+const int SETPOINT_PIN = A1;   // Analog pin for Setpoint Potentiometer
+const int SETPOINT_INDICATOR = 6; // PWM pin for indicating setpoint
+const int INPUT_INDICATOR = 5; // PWM pin for indicating Input
+
+void setup()
+{
+  Serial.begin(115200);
+  Serial.println(__FILE__);
+  myPID.SetOutputLimits(-4, 255);
+  if (SETPOINT_INDICATOR >= 0) pinMode(SETPOINT_INDICATOR, OUTPUT);
+  if (INPUT_INDICATOR >= 0) pinMode(INPUT_INDICATOR, OUTPUT);
+  Setpoint = 0;
+  //turn the PID on
+  myPID.SetMode(AUTOMATIC);
+  if(INPUT_PIN>0){
+    Input = analogRead(INPUT_PIN);
+  }else{
+    Input = simPlant(0.0,1.0); // simulate heating
+  }
+  Serial.println("Setpoint Input Output Watts");
+}
+
+void loop()
+{
+  // gather Input from INPUT_PIN or simulated block
+  float heaterWatts = (int)Output * 20.0 / 255; // 20W heater
+  if (INPUT_PIN > 0 ) {
+    Input = analogRead(INPUT_PIN);
+  } else {
+    float blockTemp = simPlant(heaterWatts,Output>0?1.0:1-Output); // simulate heating
+    Input = blockTemp;   // read input from simulated heater block
+  }
+
+  if (myPID.Compute())
+  {
+    analogWrite(PWM_PIN, (int)Output);
+
+    Setpoint = analogRead(SETPOINT_PIN) / 4; // Read setpoint from potentiometer
+    if (INPUT_INDICATOR >= 0) analogWrite(INPUT_INDICATOR, Input);
+    if (SETPOINT_INDICATOR >= 0) analogWrite(SETPOINT_INDICATOR, Setpoint);
+  }
+  report();
+}
+
+void report(void)
+{
+  static uint32_t last = 0;
+  const int interval = 1000;
+  if (millis() - last > interval) {
+    last += interval;
+    //    Serial.print(millis()/1000.0);
+    Serial.print(Setpoint);
+    Serial.print(' ');
+    Serial.print(Input);
+    Serial.print(' ');
+    Serial.print(Output);
+    Serial.print(' ');
+    Serial.print(myPID.GetIntegral());
+    Serial.print(' ');
+    Serial.println();
+  }
+}
+
+float simPlant(float Q,float hfactor) { // heat input in W (or J/s)
+  // simulate a 1x1x2cm aluminum block with a heater and passive ambient cooling
+ // float C = 237; // W/mK thermal conduction coefficient for Al
+  float h = 5 *hfactor ; // W/m2K thermal convection coefficient for Al passive
+  float Cps = 0.89; // J/g°C
+  float area = 1e-4; // m2 area for convection
+  float mass = 10 ; // g
+  float Tamb = 25; // °C
+  static float T = Tamb; // °C
+  static uint32_t last = 0;
+  uint32_t interval = 100; // ms
+
+  if (millis() - last >= interval) {
+    last += interval;
+    // 0-dimensional heat transfer
+    T = T + Q * interval / 1000 / mass / Cps - (T - Tamb) * area * h;
+  }
+  return T;
+}