// https://forum.arduino.cc/t/running-two-stepper-motors-at-once/1115352

#include <AccelStepper.h>

#define dirPinLeft 7          /// direction left
#define stepPinLeft 8         /// step left
#define dirPinRight 3         /// direction right
#define stepPinRight 4        /// step right
#define motorInterfaceType 1  /// bipolar motor

AccelStepper stepperLeft = AccelStepper(motorInterfaceType, stepPinLeft, dirPinLeft);
AccelStepper stepperRight = AccelStepper(motorInterfaceType, stepPinRight, dirPinRight);

const int enPin1 = 9;                      /// enable pin 1
const int enPin2 = 10;                     /// enable pin 2
const int buttonPin = 5;                   /// button pin
int buttonState = 0;                       /// variable for reading the pushbutton status
int processEnablerStateVariableCount = 5;  // global state variable for remembering how many times to go

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);  // Button between Pin and Ground
  pinMode(enPin1, INPUT);
  pinMode(enPin2, INPUT);
  digitalWrite(buttonPin, HIGH);  /// activate arduino internal pull up
  digitalWrite(enPin1, HIGH);     /// disable motor control
  digitalWrite(enPin2, HIGH);     /// disable motor control

  stepperLeft.setMaxSpeed(100);  /// slow is 100, fast is 900000
  stepperLeft.setAcceleration(50);
  stepperLeft.moveTo(15);
  stepperRight.setMaxSpeed(100);
  stepperRight.setAcceleration(50);
  stepperRight.moveTo(-15);
}

void loop() {
  slowMove1();
}

void slowMove1() {  /// motors are NOT disabled at end of function
  digitalWrite(enPin1, LOW);  /// enable motor control
  digitalWrite(enPin2, LOW);  /// enable motor control

  if (stepperLeft.distanceToGo() == 0 && processEnablerStateVariableCount > 0) {
    stepperLeft.moveTo(-stepperLeft.currentPosition());
    --processEnablerStateVariableCount;  /// reduce the count by one
  }
  stepperLeft.run();

  if (stepperRight.distanceToGo() == 0 && processEnablerStateVariableCount > 0) {
    stepperRight.moveTo(-stepperRight.currentPosition());
  }
  stepperRight.run();

    digitalWrite(enPin1, HIGH);  /// disable motor control
    digitalWrite(enPin2, HIGH);  /// disable motor control
}