Diff: PID.h

Revision:

0:9a6f7aafe531

Child:

2:07397aa513c6

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PID.h	Mon Nov 23 02:42:53 2015 +0000
@@ -0,0 +1,100 @@
+#ifndef PID_H
+#define PID_H
+#include "mbed.h"
+#include <algorithm>
+
+/*
+    Bryce Williams 11/19/2015
+    
+    PID Controller Class based on Brett Beauregard's Arduino PID Library
+    and PID blog post. 
+    
+    Brett Beauregard's blog post explains the PID code implementation very well
+    and discusses why the actual equation is a bit different than the classical 
+    equation, i.e. he explains and implements how to overcome windup, dervative
+    kick, etc.  This class uses the same implementation, but adds interrupt 
+    driven computation. 
+    
+    Reference Links:
+    1. Arduion Library:
+        (http://playground.arduino.cc/Code/PIDLibrary)
+    2. Brett Beauregard's PID Blog:
+        (http://brettbeauregard.com/blog/2011/04/improving-the-beginners-
+         pid-introduction/)
+*/
+
+class PID{
+    public:
+        /*
+            Constructor for PID objects. 
+            
+            Note: PID objects use given pointers, ie setpoint, 
+            feedback, output inside interrupts. When reading/ modifying
+            these vars make sure we don't have possible read/write 
+            conflicts if the interrupt fires. Either ensure reads/writes
+            are atomic operations, or call the stop() method perform the 
+            read/write and then call the start() method.
+        */
+        PID(float* setpoint, float* feedback, float* output,
+            float output_lower, float output_upper,
+            float  kp, float ki,  float kd, float Ts);
+        /*
+            Starts PID Controller; Attaches sample() as callback to Ticker 
+            sample_timer and starts the interrupt
+        */
+        void start();
+        /*
+            Stops PID Contoller; detaches callback from Ticker sample_timer.
+            Allows manual setting of output. 
+        */
+        void stop();
+        /*
+            Increments/ decrements Gain values and Sample time 
+            by the given value. Gives a simple method to 
+            programatically step through different values; just put in a 
+            loop and go
+            @param delta_"name" The value that will be added to its currently set value         
+        */
+//        void adjust_parameters(float delta_kp, float delta_ki, float delta_kd, float delta Ts);
+        /*
+            Overwrite Gain and Sample Time parameters with new 
+            values
+            Note: sample_timer interrupt is disabled during update
+                  to avoid synch issues.
+            
+        */
+        void set_parameters(float kp, float ki, float kd, float Ts);
+        
+        /*
+            returns current error
+        */
+        float getError();
+   
+    private:
+        float _kp, _ki, _kd;            // PID Gain values
+        float _Ts;                      // Sample time is seconds
+        float* _setpoint;               // Pointer to setpoint value
+        float* _feedback;               // Pointer to sensor feedback value (sensor input)
+        float* _output;                 // Pointer to control output value
+        float  _output_lower;            // Ouput Lower Limit
+        float  _output_upper;            // Output Upper Limit
+        
+        float i_accumulator;            // Integral Term accumulator
+        float last_feedback;            // Previous feedback value
+        float error;                    // Feedback error term
+        Ticker sample_timer;            // Generates the sample time interrupt and calls sample()
+        /* 
+            sample() performs next sample calculationand updates command value
+        */
+        void sample();
+        /*
+            Clips value to lower/ uppper
+            @param value    The value to clip
+            @param lower    The mininum allowable value
+            @param upper    The maximum allowable value
+            @return         The resulting clipped value
+        */
+        float clip(float value, float lower, float upper);
+};
+
+#endif
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