#include "U8glib.h"

U8GLIB_SSD1306_128X64 u8g; // hardware

int echo = 8; 
int trig = 9; 

void setup() {
  pinMode(trig, OUTPUT); // set trig output pin
  pinMode(echo, INPUT); // set echo input pin
  u8g.setFont(u8g_font_7x13); // set the font for letters
}

void loop() {
  digitalWrite(trig, HIGH); // start the measuring
  digitalWrite(trig, LOW); // low the trig

  int duration = pulseIn(echo, HIGH); // read the length of echo high
  int box_length = duration / 182; // scale factor for printing box length
  int distance = duration / 58;// pulse/58 = distance in centimeters

  u8g.firstPage(); // begin the display
  do {
    if (distance >= 200) { 
      u8g.drawStr(50, 20, "Safe"); 
    }
    else if (distance < 80) {
      u8g.drawStr(28, 20, "Too Close");
    }
    else {
      u8g.drawStr(40, 20, "Careful");
    }
    // display the box starts with upper left cordinate (0,32) and 20 height. take with as box_length which defined above
    u8g.drawBox(0, 32, box_length, 20);
  } while (u8g.nextPage());
}