Lesson 8: OLED Distance Meter

/*
  DIY KIT - Arduino Ultrasonic Distance & Parking Learning Kit
  Lesson 8 of 9: OLED Distance Meter

  LIBRARIES (once): Tools > Manage Libraries, search "Adafruit SSD1306",
  click Install, and choose "Install all" so Adafruit GFX and BusIO come too.

  WIRING (unplug the USB cable before you wire)
    The sensor from Lesson 1 (TRIG pin 9, ECHO pin 10) stays.
    OLED display - go by the labels printed on it, the order varies:
      VCC -> 5V  (+ rail)      GND -> GND (- rail)
      SDA -> UNO A4            SCL -> UNO A5
    The LEDs and buzzer can stay; this sketch does not use them.

  WHAT SHOULD HAPPEN
    The OLED shows the zone at the top, the distance in big numbers and a
    bar that grows as the target moves away (full at 100 cm).
    The Serial Monitor (9600 baud) says which address the display answered on.

  F("...") keeps text in the UNO's large program memory instead of its small
  working memory (RAM). The display needs 1 KB of RAM for its picture.
*/

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

const int TRIG_PIN = 9;
const int ECHO_PIN = 10;

const int CLEAR_CM = 50;      // the same zones as Lessons 2 and 3
const int NEAR_CM = 20;
const int BAR_FULL_CM = 100;  // the bar is full width at this distance

const unsigned long ECHO_TIMEOUT_US = 30000;
const int MIN_CM = 2;
const int MAX_CM = 400;

Adafruit_SSD1306 display(128, 64, &Wire, -1);   // 128 x 64 pixels, no reset pin
bool displayOk = false;

long readOnceCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  unsigned long us = pulseIn(ECHO_PIN, HIGH, ECHO_TIMEOUT_US);
  if (us == 0) return 0;
  long cm = us / 58;
  if (cm < MIN_CM || cm > MAX_CM) return 0;
  return cm;
}

// Most of these displays answer at address 0x3C, some at 0x3D. Try both.
bool startDisplay() {
  if (display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("OLED found at 0x3C"));
    return true;
  }
  if (display.begin(SSD1306_SWITCHCAPVCC, 0x3D)) {
    Serial.println(F("OLED found at 0x3D"));
    return true;
  }
  Serial.println(F("OLED not found - unplug USB and check VCC, GND, SDA (A4) and SCL (A5)"));
  return false;
}

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  Serial.begin(9600);
  Serial.println(F("Lesson 8: OLED Distance Meter"));
  displayOk = startDisplay();
  if (displayOk) {
    display.clearDisplay();
    display.setTextColor(SSD1306_WHITE);
    display.display();
  }
}

void loop() {
  long cm = readOnceCm();
  Serial.println(cm);                       // 0 means no echo

  if (displayOk) {
    display.clearDisplay();

    // Top line: the zone, in small letters.
    display.setTextSize(1);
    display.setCursor(0, 0);
    if (cm == 0)            display.print(F("NO ECHO"));
    else if (cm < NEAR_CM)  display.print(F("NEAR"));
    else if (cm < CLEAR_CM) display.print(F("CAUTION"));
    else                    display.print(F("CLEAR"));

    // Middle: the distance, 3 times bigger.
    display.setTextSize(3);
    display.setCursor(0, 22);
    if (cm == 0) {
      display.print(F("--"));
    } else {
      display.print(cm);
      display.setTextSize(2);
      display.print(F(" cm"));
    }

    // Bottom: a bar, full width at BAR_FULL_CM.
    if (cm > 0) {
      int width = map(constrain(cm, 0, BAR_FULL_CM), 0, BAR_FULL_CM, 0, 128);
      display.fillRect(0, 56, width, 8, SSD1306_WHITE);
    }
    display.display();                      // nothing appears until display() is called
  }

  delay(150);
}