Control DC gear motor using a rotary encoder - arduino

Question

I have a rotary encoder and a DC gear motor connected to my Arduino UNO. I would like to rotate the DC motor at a certain angle. As I right now, I have written a code that reads the position of my encoder as I rotate it and prints out the position and the angle. I have also written code that runs the dc motor at fixed amount of time.
I would like to rotate the dc motor at a certain angle. For example, if I input 90 degrees my motor should rotate 90 degrees and stop.
I'm using pin 2 and pin 3 for my channel A and B (ENCODER)
I'm using pin 9 to control my dc motor.
I have no clue how to approach this... any thoughts?
#include <LiquidCrystal.h>
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);
int lcd_case = 0;
volatile int timeToRun = 0;
int motorPin = 6;
#define BTN_RIGHT 0
#define BTN_LEFT 1
#define BTN_UP 2
#define BTN_DOWN 3
#define BTN_SELECT 4
#define BTN_NONE 5
#define SELECT 6
#define RESET 7
#define PIN
#define encoderPinA 2
#define encoderPinB 3
#define CPR 256
volatile int counter =0;
volatile boolean flag;
volatile int var_degrees =0;
void setup() {
pinMode(3, OUTPUT);
pinMode(encoderPinA, INPUT);
pinMode(encoderPinB, INPUT);
Serial.begin (9600);
attachInterrupt(digitalPinToInterrupt(encoderPinA), isr_2, RISING);
lcd.clear();
}
void loop() {
if(flag == true){
var_degrees = ((360/256.0)*counter);
Serial.println(var_degrees);
//lcd.setCursor(0, 1);
//lcd.print("Degrees: ");
//lcd.setCursor(9, 1);
//lcd.print(var_degrees);
flag = false;
}
lcd_case = readButtons();
int read_button = analogRead (0);
//Depending on which button we pressed, we performan action
switch (lcd_case) {
case BTN_RIGHT:
{
break;
}
case BTN_LEFT:
{
break;
}
case BTN_UP:
{
timeToRun = timeToRun +1;
lcd.setCursor(0, 1);
lcd.print("Degrees: ");
lcd.setCursor(9, 1);
lcd.print(timeToRun);
delay(500);
break;
}
case BTN_DOWN:
{
if (timeToRun > 0) {
timeToRun = timeToRun - 1;
lcd.setCursor(0, 1);
lcd.print("Degrees: ");
lcd.setCursor(9, 1);
lcd.print(timeToRun);
delay(500);
break;
}
}
case BTN_SELECT:
{
analogWrite(motorPin, 255);
// I NEED TO ROTATE MOTOR BASED ON ANGLE IN ENCODER
delay(timeToRun * 100); //ONLY ROTATES DC MOTOR IN SECONDS
break;
}
case RESET:
{
break;
}
}
}
//Interrupts
void isr_2(){
flag = true;
if(digitalRead(encoderPinA) == HIGH){
if(digitalRead(encoderPinB) == LOW){
counter = counter -1; //COUNTER CLOCK WISE
}
else{
counter = counter +1; //CLOCK WISE
}
}
else{ //IF PIN A IS LOW
if(digitalRead(encoderPinB) == LOW){
counter = counter +1; //CLOCK WISE
}
else{
counter = counter -1 ; //COUNTER CLOCK WISE
}
}
}
int readButtons() {
int read_button;
read_button = analogRead (0);
if (read_button < 50) {
return BTN_RIGHT;
}
if (read_button < 195) {
return BTN_UP;
}
if (read_button < 400) {
return BTN_DOWN;
}
if (read_button < 600) {
return BTN_LEFT;
}
if (read_button < 800) {
return BTN_SELECT;
}
else
return BTN_NONE;
}

Answer 1

It's good that you are correctly reading the position of the armature of your motor. Now is the time to use PID and closed loop! Tuned PID is a controller that helps your motor to go to the desired position at the best possible time with the lowest possible overshoot(error) It takes a control course to learn all of this. You will basically need a feedback loop that takes the "desired angle", give it to the controller which moves the motor. Then you get the current position of the motor, which will be fed back to the origin of the system. Your "desired angle" minus "current angle" will be how much your motor should move each time the micro controller go over the loop.
Here is how the feedback loop looks like:
And here is link to learn control. Good luck!
Control Tutorials
Edit 2: I should probably give you an intro on what PID is as well. PID controller is made of three different components:
Proportional
Integral
Derivative
Each time you get your "Desired Angle" - "Actual Angle" or "e" as shown in diagram, you will times it by Kp. Find its derivative with respect to previous e and times it by Kd, and find the integral of the errors and times it by Ki. You can start by ignoring Ki and integral, and add it if it was needed later. After you got Kpe+Kdd(e)/dt, this values is the percentage of power you will output to your motor. Kp and Kd and Ki is where the real engineering comes into play. You should find them using the transfer function of your system and fine-tune them in MatLab or a similar software. These values are usually low (less than 1). It really depends on your system. For my motor, they were Kp=0.001 and Kd=0.02