#include <Servo.h>

Servo arm;
float pos = 0.0;
float step = 30.0;
bool increasing = true;

void setup()
{
  pinMode(A1, INPUT_PULLUP);
  arm.attach(2);
  arm.write(pos);
}

void loop()
{
  if (!digitalRead(A1))
  {
    if (increasing)
    {
      pos += step;
      if (pos >= 180)
      {
        pos = 180;
        increasing = false;
      }
    }
    else
    {
      pos -= step;
      if (pos <= 0)
      {
        pos = 0;
        increasing = true;
      }
    }

    arm.write(pos);
    delay(300);
  }
}