PID controller using dc motor and encoder without PID library

Projects General Guidance
1

hello, this is my first post here and I hope someone can help me. I am doing a project where i am supposed to create PID controller of a dc motor using rotary encoder. I got the part where I am supposed to calculate rmp but I am straggling with PID. In addition, I am trying to figure it out how to put desirable speed through serial port and still get the reading from rpm and PID reading I am new to this and still learning thanks so much for help. this is the code that I am having right now

#include <AFMotor.h>
 AF_DCMotor motor(2, MOTOR12_2KHZ);
volatile int rpmcount = 0;
int rpm = 0;
unsigned long lastmillis = 0;

  int pid_speed=0;
  float kp=2.25;
  float ki=.01;
  float kd=0.005;
  int prev_error=0;
  double pwm_sig=0;
  int error=0;
  float desired_rpm=80;
  int diff = 0;

  
void setup(){
 Serial.begin(9600); 
 attachInterrupt(0, rpm_fan, FALLING);//interrupt cero (0) is on pin two(2).
 motor.run(FORWARD);

}
void loop(){
 
 //if (Serial.available()){
   //int speed = Serial.parseInt();
   // if (speed >= 0 && speed <= 255) {
     //motor.setSpeed(speed);
    // motor.run(FORWARD);

     // Serial.print("target=\t");
     // Serial.print(speed);
  //  }  
// }
 
 if (millis() - lastmillis == 1000){  //upade one sec
 detachInterrupt(0);    //Disable interrupt
 
 rpm = (rpmcount * 3)/6;  // Convert to RPM 

 Serial.print("RPM =\t"); 
 Serial.print(rpm); // print the rpm value.
 
 
 rpmcount = 0; // Restart RPM counter
 lastmillis = millis(); // Uptade lasmillis
 attachInterrupt(0, rpm_fan, FALLING); //enable interrupt
   }
   error=desired_rpm-rpm;

      diff += error;
      pid_speed = kp*error; + ki*diff;

      pid_speed=(int)pid_speed;

      Serial.print(pid_speed);
      Serial.print("       ");
      if (pid_speed> 0){
        if (pid_speed<255)
         motor.setSpeed(255);
        else
          motor.setSpeed(pid_speed);
      }
      if(pid_speed<0){
        if(pid_speed<-255)
        {
           motor.setSpeed(0); 
        }
        else
       {
          pid_speed=abs(pid_speed);
          motor.setSpeed(255-pid_speed);
       }
      }
      Serial.print ("      ");
      Serial.println(rpm);
}

void rpm_fan(){
  rpmcount++;
}
2 
    pid_speed = kp*error; + ki*diff;

Code like this will certainly add to the "straggle" as it shouldn't compile. Get rid of the extra ";".

Why do you think you need the "I" term? Start with just P.

3

You may be interested in this Thread about my PID explorations. I did get it working (around Reply #72 i think)

...R