How to change the direction of a stepper motor using the AccelStepper library?

Question

I'm using a Nema 17 stepper motor (200 steps) and a DRV8825 motor driver. This is the configuration I am using:

I am using a 9 V power supply. The dirPin is connected to pin 3 on the Arduino board, and my stepPin to pin 2.

What I'm trying to do is move the motor 100 steps clockwise and then move it 100 steps anti-clockwise, so that it returns to the starting position. This is the code I am using:

#include <AccelStepper.h>
#define dirPin 3
#define stepPin 2
#define motorInterfaceType 1
int SPR = 200;
AccelStepper stepper(motorInterfaceType, stepPin, dirPin);
void setup() {
  pinMode(dirPin,OUTPUT);
  pinMode(stepPin,OUTPUT);
  // put your setup code here, to run once:
  stepper.setMaxSpeed(200);
  stepper.setAcceleration(30);
}
void loop() {
  // put your main code here, to run repeatedly:
  stepper.moveTo(100);
stepper.runToPosition();
  delay(1000);
stepper.moveTo(-100);
stepper.runToPosition();
  delay(1000);
}

I have two issues:

1. Before moving the motor 100 steps, it moves a couple of steps (like 15°), and then it starts moving, first 100 steps, and then 200 steps. That would be the first iteration, and I don't understand why it moves those 200 steps. And then, in the following iterations, the motor just moves 200 steps.

2. It only moves in one direction. I can't get it to move anti-clockwise.

Answer 1

The moveTo() function takes absolute positions, so if you want to move in both directions, you should adjust the target positions accordingly.

You can modify your loop() function as follows:

void loop() {
  stepper.moveTo(100);
  stepper.runToPosition();
  delay(1000);
stepper.moveTo(0); // Move back to the starting position
  stepper.runToPosition();
  delay(1000);
}