How to get the last value from previous running

Projects Programming
1

I am using an Encoder motor and PID logic to control its position like a servo motor. The code attached below is working fine.

I want to save the value of the pos variable in the code, so that when I restart the program next time, I can retrieve that saved value. Currently, its value is zero when i start the program. How can I do this?

I want that the motor should be set at a certain position whenever i start the arduino UNO. So for eg if it was left at 240degrees the last time i ran the program, I restart the Arduino and the motor turns back at zero position. This I can only do If i have the last pos value saved and turn the motor accordingly.

Or is there any other method for this?

This is the motor I'm using: https://www.aliexpress.com/item/32612296812.html
I'm using it with L298N Motor Driver

#define ENCA 2 
#define ENCB 3 
#define PWM 5
#define IN2 6
#define IN1 7

int turns = 0; 
int target;
int pos;
long prevT = 0;
float eprev = 0;
float eintegral = 0;

void setup() {
  Serial.begin(9600);
  pinMode(ENCA,INPUT);
  pinMode(ENCB,INPUT);
  attachInterrupt(digitalPinToInterrupt(ENCA),readEncoder,RISING);
  Serial.println("target pos");
}

void loop() {
  if (Serial.available() >0) {
    int x = Serial.parseInt();
    target = x;
  }
  
  //target = 250*sin(prevT/1e6);

  // PID constants
  float kp = 1;
  float kd = 0.026;
  float ki = 0.02;

  // time difference
  long currT = micros();
  float deltaT = ((float) (currT - prevT))/( 1.0e6 );
  prevT = currT;

  // error
  int e = pos-target;

  // derivative
  float dedt = (e-eprev)/(deltaT);

  // integral
  eintegral = eintegral + e*deltaT;

  // control signal
  float u = kp*e + kd*dedt + ki*eintegral;
  Serial.print(u);
  Serial.print(" ");

  // motor power
  float pwr = fabs(u);
  if( pwr > 255 ){
    pwr = 255;
  }

  // motor direction
  int dir = 1;
  if(u<0){
    dir = -1;
  }

  // signal the motor
  setMotor(dir,pwr,PWM,IN1,IN2);

  // store previous error
  eprev = e;

  Serial.print(target);
  Serial.print(" ");
  Serial.println(pos);
}

void setMotor(int dir, int pwmVal, int pwm, int in1, int in2){
  analogWrite(pwm,pwmVal);
  if(dir == 1){
    digitalWrite(in1,HIGH);
    digitalWrite(in2,LOW);
  }
  else if(dir == -1){
    digitalWrite(in1,LOW);
    digitalWrite(in2,HIGH);
  }
  else{
    digitalWrite(in1,LOW);
    digitalWrite(in2,LOW);
  }  
}

void readEncoder(){
  int b = digitalRead(ENCB);
  if(b > 0){
    pos++;
  }
  else{
    pos--;
  }
}
2

you could attach an adafruit-i2c-fram memory device - save your data to it during normal operation - restore data on power up

3

You could save the position to Flash every time the motor stops, but depending on how often you start/stop, that could cause issues with the Flash write limits.
Alternately, you could have a pushbutton that says "I'm shutting down now, save my position."

Those are the two easy ways.

4

You don't say what Arduino you're using. Nano, Uno, Mega, look at saving to EEPROM.

5

Often the zero position is marked with a limit switch. That way if the motor is moved while the power is off it can still return to the same zero position.

6

Arduino Uno. I did mention it btw.
And what difference does it even make btw?

7

Sorry, I missed the reference. But, there are many Arduino products, only some of which have EEPROM, others have other mechanisms for non-volatile storage. Short answer is, my answer would be irrelevant and misleading if your particular Arduino didn't have EEPROM.
That said, have you now looked at the EEPROM tutorial?

8

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