#### wakaka

##### Full Member level 4

Code:

```
#include <string.h>
#include <stdio.h>
/*=====================================================
PID Function
The PID function is used in mainly
control applications. PIDCalc performs one iteration of the PID
algorithm.
While the PID function works, main is just a dummy program showing
a typical usage.
======================================================*/
typedef struct PID {
double SetPoint; // Desired Value
double Proportion; // Proportional Const
double Integral; // Integral Const
double Derivative; // Derivative Const
double LastError; // Error[-1]
double PrevError; // Error[-2]
double SumError; // Sums of Errors
} PID;
/*=====================================================
PID
======================================================*/
double PIDCalc( PID *pp, double NextPoint )
{
double dError,
Error;
Error = pp->SetPoint - NextPoint;
pp->SumError += Error;
dError = pp->LastError - pp->PrevError;
pp->PrevError = pp->LastError;
pp->LastError = Error;
return (pp->Proportion * Error
+ pp->Integral * pp->SumError
+ pp->Derivative * dError
);
}
/*=====================================================
Initialize PID Structure
======================================================*/
void PIDInit (PID *pp)
{
memset ( pp,0,sizeof(PID));
}
/*=====================================================
Main Program
======================================================*/
double sensor (void) // Dummy Sensor Function
{
return 100.0;
}
void actuator(double rDelta) // Dummy Actuator Function
{}
void main(void)
{
PID sPID; // PID Control Structure
double rOut; // PID Response (Output)
double rIn; // PID Feedback (Input)
PIDInit ( &sPID ); // Initialize Structure
sPID.Proportion = 0.5; // Set PID Coefficients
sPID.Integral = 0.5;
sPID.Derivative = 0.0;
sPID.SetPoint = 100.0; // Set PID Setpoint
for (;;) { // Mock Up of PID Processing
rIn = sensor (); // Read Input
rOut = PIDCalc ( &sPID,rIn ); // Perform PID Interation
actuator ( rOut ); // Effect Needed Changes
}
}
```

I not quite understand in some parts this code, can some explain on it??

1.

Code:

```
double PIDCalc( PID *pp, double NextPoint )
{
double dError,
Error;
Error = pp->SetPoint - NextPoint;
pp->SumError += Error;
dError = pp->LastError - pp->PrevError;
pp->PrevError = pp->LastError;
pp->LastError = Error;
return (pp->Proportion * Error
+ pp->Integral * pp->SumError
+ pp->Derivative * dError
);
}
```

2.

Code:

```
void PIDInit (PID *pp)
{
memset ( pp,0,sizeof(PID));
}
```

3.

Code:

```
void main(void)
{
PID sPID; // PID Control Structure
double rOut; // PID Response (Output)
double rIn; // PID Feedback (Input)
PIDInit ( &sPID ); // Initialize Structure
sPID.Proportion = 0.5; // Set PID Coefficients
sPID.Integral = 0.5;
sPID.Derivative = 0.0;
sPID.SetPoint = 100.0; // Set PID Setpoint
for (;;) { // Mock Up of PID Processing
rIn = sensor (); // Read Input
rOut = PIDCalc ( &sPID,rIn ); // Perform PID Interation
actuator ( rOut ); // Effect Needed Changes
}
}
```

sPID.Proportion , the '.' means????

if possible do explain the whole thing, thanx......