PI controller using PIC16F876A

This topic has 5 replies, 2 voices, and was last updated 10 years, 1 month ago by Ligo George.

Viewing 6 posts - 1 through 6 (of 6 total)

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September 6, 2014 at 12:45 pm #8887
biswaIITH
Participant
hello ligo,,i am trying to implement PI controller for controlling the output voltage of a dc/dc converter using PIC16F876A .
This z d code what i have written
```
float adc;
float set_ref=60;
float err_val=0,I_err=0;
float current_duty_2=10;
float Kp=.01,Ki=2;
float P_term=0,I_term=0;
float Sum_err=0;
void main() {
ADCON1=0x81;
TRISA=0xFF;
TRISC.F1=0;
PWM2_Init(100000);
PWM2_Start();
PWM2_Set_Duty(current_duty_2);
while(1)
{
adc=ADC_Read(1)/4;
err_val=adc-set_ref;
P_term=Kp*err_val;
I_err=I_err+err_val;
if(I_err>10)
I_err=10;
else if(I_err255)
Sum_err=255;
else if(Sum_err<0)
Sum_err=0;
current_duty_2=Sum_err;
PWM2_Set_Duty(current_duty_2);
}
}
```
MY DOUBT IS IN THE WHILE LOOP AFTER EXECUTING THE LAST INSTRUCTION i.e. PWM2_Set_Duty(current_duty_2), IT WILL GO BACK TO THE STARTING OF THE LOOP TO EXECUTE THE INSTRUCTION adc=ADC_Read(1)/4; AT THE SAME TIME IT SHOULD ACCEPT THE ADC VALUE. WHAT I MEAN IS, ADC CONVERSION TIME AND EXECUTION TIME FOR REST OF INSTRUCTIONS MUST BE SAME.I AM CONFUSED AS TO HOW TO DO THAT. WE MAY FIX ADC CONVERSION TIME BUT THE EXECUTION TIME FOR THE REST OF INSTRUCTIONS MAY VARY IN EACH ITERATION AS IT CONTAINS LOOPS AND CONDITIONS. I WANT BOTH EXECUTION AND INSTRUCTION TO HAPPEN SYNCHRONOUSLY.
September 6, 2014 at 6:47 pm #9025

Ligo George
Keymaster

Then you should write your own ADC Codes.
Try the following link, it uses PIC 16F877A and Hi-Tech C.
Using ADC with PIC Microcontroller with Hi-Tech C

September 28, 2014 at 1:14 am #9030

biswaIITH
Participant

Can we compile the above hitech c code in mikroc 6.4 …thanksss

September 28, 2014 at 2:43 pm #9031
Ligo George
Keymaster
You need to make some changes as given below.
```
void myADC_Init()
{
  ADCON0 = 0x41;                                //ADC Module Turned ON and Clock is selected
  ADCON1 = 0xC0;                                //All pins as Analog Input
  //With reference voltages VDD and VSS
}

unsigned int myADC_Read(unsigned char channel)
{
  if(channel > 7)                                     //If Invalid channel selected
    return 0;                                              //Return 0

  ADCON0 &= 0xC5;                             //Clearing the Channel Selection Bits
  ADCON0 |= channel<<3;                  //Setting the required Bits
  Delay_ms(2);                                      //Acquisition time to charge hold capacitor
  ADCON0.F2 = 1;                                 //Initializes A/D Conversion
  while(ADCON0.F2);                           //Wait for A/D Conversion to complete
    return ((ADRESH<<8)+ADRESL);   //Returns Result
}
```
October 12, 2014 at 4:14 pm #9555

biswaIITH
Participant

ADCON0 &= 0xC5; //Clearing the Channel Selection Bits
ADCON0 |= channel< <3; //Setting the required Bits

why are these two instructions required???I mean to say what is the need of clearing and setting the channel selection bits again n again..We can select once ryt!!!correct me if i am wrong

October 16, 2014 at 7:49 pm #9654

Ligo George
Keymaster

Note that required bits are SET using OR Operator, so we should clear previously set bit if any using AND Operator.
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