#include <SoftwareSerial.h>
#include <Stepper.h>

SoftwareSerial serial_sw(10, 9); //tx, rx

const int stepsPerRevolution = 200;

Stepper myStepper(stepsPerRevolution, 0, 1, 3, 4);

void setup() {
serial_sw.begin(9600);
}

byte distance;

void loop() {
if (serial_sw.available() > 0) {
  distance = serial_sw.read();
  int motorSpeed = map(distance, 0, 255, 0, 200);
if (motorSpeed > 7) {
  myStepper.setSpeed(50);
  myStepper.step(10);
} else if (motorSpeed <= 7) {
myStepper.setSpeed(0);
myStepper.step(0);
}
}
}