PID library

app_pid.c

/*app examle */
#include "pid.h"
PID pid;
double vInput, vSetpoint, pwmOutput;
double kp = 3, ki = 7, kd = 0.1, sampleTime = 100;
 
/* initilize pid in initilization function */
void APP_Init()
{
    vInput = SENSOR_Read();
    vSetpoint = 30; /*Set voltage at 30V*/
    PID_Init(&pid, &vInput, &pwmOutput, &vSetpoint, kp, ki, kd, sampleTime, PID_REVERSE);
}
 
/*Call every sample time (in milisecond)*/
 
void TaskEvery100ms()
 
{
 
    //Read sensor to vInput
    vInput = SENSOR_Read();
 
    //Calculate PID
    PID_Compute(&pid);
 
    //Set PWM duty
    PWM_SetDuty(pwmOutput);
 
}
void APP_SetVref(double volt)
{
    vSetpoint = volt;
}

pid.c

/*
    PID Library
    Copyright @2013 vidieukhien.net forum
*/
#include "pid.h"
 
void PID_SetOutputLimits(PID *pid, double min, double max)
{
    pid->outMin = min;
    pid->outMax = max;
    if(pid->lastProcessValue < min)
        pid->lastProcessValue = min;
    if(pid->lastProcessValue > max)
        pid->lastProcessValue = max;
    if(*pid->output < min)
        *pid->output = min;
    if(*pid->output > max)
        *pid->output = max;
}
 
 
void PID_SetTunings(PID *pid, double kp, double ki, double kd, uint8_t direction)
{
    float sampleTimeInSec = pid->sampleTime/1000.0;
    pid->kp = kp;
    pid->ki = ki * sampleTimeInSec;
    pid->kd = kd / sampleTimeInSec;
    if(direction == PID_REVERSE) {
        pid->kp = -pid->kp;
        pid->ki = -pid->ki;
        pid->kd = -pid->kd;
    }
}
 
void PID_Init(PID *pid, double *input, double *output, double *setPoint, double kp, double ki, double kd, double sampleTimeMs, uint8_t direction)
{
    pid->input = input;
    pid->output = output;
    pid->setPoint = setPoint;
    pid->lastInput = *input;
    pid->lastProcessValue = *output;
    pid->sampleTime = sampleTimeMs;
    PID_SetTunings(pid, kp, ki, kd, direction);
    PID_SetOutputLimits(pid, 100, 1000);
}
 
void PID_Compute(PID *pid)
{
    double input, error, dinput, output;
    input = *pid->input;
    error = *pid->setPoint - input;
    pid->lastProcessValue += (pid->ki * error);
    if(pid->lastProcessValue > pid->outMax)
        pid->lastProcessValue = pid->outMax;
    if(pid->lastProcessValue < pid->outMin)
        pid->lastProcessValue = pid->outMin;
    dinput = input - pid->lastInput;
    output = pid->kp * error + pid->lastProcessValue - pid->kd * dinput;
    if(output > pid->outMax)
        output = pid->outMax;
    if(output < pid->outMin)
        output = pid->outMin;
    *pid->output = output;
    pid->lastInput = input;
}

pid.h

/*
    PID Library
    Copyright @2013 vidieukhien.net forum
*/
#ifndef _PID_H_
#define _PID_H_
#include <stdint.h>
 
#define PID_DIRECT    0
#define PID_REVERSE    1
typedef struct {
        double kp;
        double ki;
        double kd;
        double *input;
        double *output;
        double *setPoint;
        double outMin;
        double outMax;
        double lastInput;
        double lastProcessValue;
        double sampleTime;
} PID;
 
void PID_Init(PID *pid, double *input, double *output, double *setPoint, double kp, double ki, double kd, double sampleTimeMs, uint8_t direction);
void PID_SetOutputLimits(PID *pid, double min, double max);
void PID_Compute(PID *pid);
void PID_SetTunings(PID *pid, double kp, double ki, double kd, uint8_t direction);
#endif