#define TRIG_PIN 10
//US Sensor TRIG PIN = D10
#define ECHO_PIN 11
//US Sensor's ECHO PIN = D11
//US Sensor & OLED Display @5V
//OLED's SDA=A4
//OLED's SCL=A5

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire);

int distance_mm;
unsigned long measured_time;

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN,  INPUT);
 Serial.begin(9600);

  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 Allocation Failed"));
    for (;;);
  }
  display.clearDisplay();
display.setTextColor(WHITE);
display.setCursor(32, 12);
display.print("STARTING...");
 display.display();
  delay(2000);
}

void loop() {

  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(20);
  digitalWrite(TRIG_PIN, LOW);
  measured_time = pulseIn(ECHO_PIN, HIGH);
  distance_mm = (int)((float)measured_time / 5.83);


display.clearDisplay();
display.setTextColor(WHITE);
display.setCursor(8, 0);
display.setTextSize(2);
  if (distance_mm < 100) display.print(" ");
  if (distance_mm <  10) display.print(" ");
display.print(distance_mm);
display.setTextSize(1);
display.setCursor(97, 8);
display.print("mm");
display.drawLine(8, 27, 108, 27, WHITE); // 1000mm Bar graph
display.fillRect(8, 28, 8 + int(distance_mm + 0.5) / 10, 30, WHITE);
display.drawLine(8, 31, 108, 31, WHITE);

display.display();
  delay(200);
}