Ultrasonic Distance Meter

// Distance meter: point the ultrasonic sensor at a wall and the screen shows// how far away it is, in feet and inches, about 3 times a second.//// Ultrasonic sensor (HC-SR04), 4 female-to-male wires://   Vcc -> 5V     Trig -> pin 7     Echo -> pin 8     Gnd -> GND// Trig and Echo can go in pins 7 and 8 either way round: the Echo pin rests// LOW while the sensor has power, so the program looks for that and uses// whichever pin it finds as Echo.//// Screen (LCD1602), pin by pin. Pin 1 is the one marked VSS://    1 VSS -> GND         2 VDD -> A0          3 V0 -> pin 9       4 RS -> pin 12//    5 RW  -> A1          6 E   -> pin 11      7 to 10 -> nothing//   11 D4  -> pin 5      12 D5  -> pin 4      13 D6 -> pin 3      14 D7 -> pin 2//   15 A   -> pin 10     16 K   -> A2// A0 powers the screen and A1/A2 act as ground, so every screen pin gets its// own wire and the Arduino's 5V and GND pins are free for the sensor.//// The sensor works from about 1 inch to about 13 feet. Aim it straight at a// flat wall: the sound spreads out in a cone, so furniture in the way can// answer first.//// From the computer://   "c 40"   sets the screen contrast, 0 to 255 (lower = darker letters)//   "b 160"  sets the backlight brightness, 0 to 255// Both are saved, so they stay the same on battery.#include <EEPROM.h>// ---------- Pins ----------const byte SENSOR_PINS[2] = {7, 8};byte trigPin = 7;byte echoPin = 8;const byte LCD_POWER = A0;const byte LCD_RW = A1;const byte LCD_GROUND = A2;  // the backlight's K pinconst byte LCD_RS = 12;const byte LCD_E = 11;const byte LCD_DATA[4] = {5, 4, 3, 2};  // the screen's D4, D5, D6, D7const byte LCD_CONTRAST = 9;const byte LCD_LIGHT = 10;// ---------- Measuring ----------// Sound takes about 148 microseconds to go 1 inch out and back at room temperature.const float MICROS_PER_INCH = 148.0;const unsigned long NO_ECHO = 0xFFFFFFFF;const byte READINGS = 5;  // take 5 and keep the middle one, to ignore stray echoes// ---------- Saved settings ----------struct Settings {  byte check;  byte contrast;  byte backlight;};const byte SETTINGS_CHECK = 0xD5;Settings settings;void setup() {  Serial.begin(9600);  Serial.println("Distance meter starting");  EEPROM.get(0, settings);  if (settings.check != SETTINGS_CHECK) {    settings = {SETTINGS_CHECK, 40, 160};    EEPROM.put(0, settings);  }  // Pins 9 and 10 flicker on and off very fast to set contrast and brightness.  // Making them flicker faster (31,000 times a second) keeps the screen steady.  TCCR1B = (TCCR1B & 0b11111000) | 0b001;  pinMode(LCD_CONTRAST, OUTPUT);  pinMode(LCD_LIGHT, OUTPUT);  analogWrite(LCD_CONTRAST, settings.contrast);  analogWrite(LCD_LIGHT, settings.backlight);  // Ground pins first, then switch the screen's power on.  pinMode(LCD_RW, OUTPUT);  digitalWrite(LCD_RW, LOW);  pinMode(LCD_GROUND, OUTPUT);  digitalWrite(LCD_GROUND, LOW);  pinMode(LCD_POWER, OUTPUT);  digitalWrite(LCD_POWER, HIGH);  delay(100);  lcdBegin();  lcdPrintAt(0, 0, " Distance meter ");  lcdPrintAt(0, 1, "  Aim at a wall ");  findSensorPins();  delay(1000);}void loop() {  readComputer();  unsigned long echoTime = measureMicros();  if (echoTime == NO_ECHO) findSensorPins();  // in case the wires were swapped or plugged in late  // Repeat the screen's start-up routine before every update, so a screen  // that had a glitch gets back in step.  lcdWake();  if (echoTime == NO_ECHO) {    showLines("  Out of range  ", " (max ~13 feet) ");    Serial.println("Out of range");  } else if (echoTime < MICROS_PER_INCH) {    showLines("   Too close    ", "  (min 1 inch)  ");    Serial.println("Too close");  } else {    showDistance(echoTime / MICROS_PER_INCH);  }}// ---------- Measuring ----------// Works out which of pins 7 and 8 is Echo: with a pull-up on, the Echo pin// still reads LOW because the sensor holds it there; the Trig pin reads HIGH.// If it can't tell (sensor unplugged, or busy), it keeps the last choice.void findSensorPins() {  pinMode(SENSOR_PINS[0], INPUT_PULLUP);  pinMode(SENSOR_PINS[1], INPUT_PULLUP);  delay(2);  bool low0 = digitalRead(SENSOR_PINS[0]) == LOW;  bool low1 = digitalRead(SENSOR_PINS[1]) == LOW;  if (low0 != low1) {    echoPin = low0 ? SENSOR_PINS[0] : SENSOR_PINS[1];    trigPin = low0 ? SENSOR_PINS[1] : SENSOR_PINS[0];  }  pinMode(echoPin, INPUT);  pinMode(trigPin, OUTPUT);  digitalWrite(trigPin, LOW);}// Measures 5 times and returns the middle echo time, in microseconds.unsigned long measureMicros() {  unsigned long times[READINGS];  for (byte i = 0; i < READINGS; i++) {    times[i] = echoMicros();    delay(60);  // the sensor needs a short rest between measurements  }  // Sort them, smallest first.  for (byte i = 1; i < READINGS; i++) {    for (byte j = i; j > 0 && times[j] < times[j - 1]; j--) {      unsigned long swap = times[j];      times[j] = times[j - 1];      times[j - 1] = swap;    }  }  return times[READINGS / 2];}// Sends out a click of sound and times how long the echo takes to come back.// Returns NO_ECHO if nothing came back within about 16 feet.unsigned long echoMicros() {  digitalWrite(trigPin, LOW);  delayMicroseconds(2);  digitalWrite(trigPin, HIGH);  delayMicroseconds(10);  digitalWrite(trigPin, LOW);  unsigned long microseconds = pulseIn(echoPin, HIGH, 30000);  return microseconds == 0 ? NO_ECHO : microseconds;}// ---------- Showing it ----------// Shows e.g.   12 ft  4.5 in//              148.5 inchesvoid showDistance(float inches) {  long tenths = lround(inches * 10);  // whole distance in tenths of an inch  int feet = tenths / 120;  int leftoverTenths = tenths % 120;  char top[17], bottom[17], number[8];  snprintf(top, sizeof(top), "%2d ft %2d.%d in", feet, leftoverTenths / 10, leftoverTenths % 10);  dtostrf(tenths / 10.0, 5, 1, number);  snprintf(bottom, sizeof(bottom), "%s inches", number);  showLines(top, bottom);  Serial.print(top);  Serial.print("   (");  Serial.print(bottom);  Serial.println(")");}// Puts one line on each row, centered, blanking out anything left over.void showLines(const char *top, const char *bottom) {  const char *lines[2] = {top, bottom};  for (byte row = 0; row < 2; row++) {    char line[17];    byte length = strlen(lines[row]);    if (length > 16) length = 16;    byte left = (16 - length) / 2;    memset(line, ' ', 16);    memcpy(line + left, lines[row], length);    line[16] = '\0';    lcdPrintAt(0, row, line);  }}// ---------- Settings from the computer ----------void readComputer() {  static char line[20];  static byte length = 0;  while (Serial.available()) {    char ch = Serial.read();    if (ch == '\n' || ch == '\r') {      line[length] = '\0';      if (length > 0) handleCommand(line);      length = 0;    } else if (length < sizeof(line) - 1) {      line[length++] = ch;    }  }}void handleCommand(const char *line) {  int value = constrain(atoi(line + 1), 0, 255);  if (line[0] == 'c') {    settings.contrast = value;    analogWrite(LCD_CONTRAST, settings.contrast);  } else if (line[0] == 'b') {    settings.backlight = value;    analogWrite(LCD_LIGHT, settings.backlight);  } else {    return;  }  EEPROM.put(0, settings);  Serial.print("Saved: contrast ");  Serial.print(settings.contrast);  Serial.print(", backlight ");  Serial.println(settings.backlight);}// ---------- Screen ----------// The screen takes letters 4 bits at a time on its D4-D7 pins. RS picks// between a command (LOW) and a letter (HIGH), and a pulse on E sends it.void lcdBegin() {  pinMode(LCD_RS, OUTPUT);  pinMode(LCD_E, OUTPUT);  for (byte i = 0; i < 4; i++) pinMode(LCD_DATA[i], OUTPUT);  digitalWrite(LCD_E, LOW);  digitalWrite(LCD_RS, LOW);  delay(50);  // give the screen time to wake up  lcdWake();  lcdSend(0x01, false);  // clear the screen  delay(2);}// The screen's start-up routine: whatever state it's in, this switches it// into 4-bit mode with 2 lines of text. It doesn't clear the screen, so it// can be repeated without any flicker.void lcdWake() {  digitalWrite(LCD_RS, LOW);  lcdNibble(0x3);  delay(5);  lcdNibble(0x3);  delayMicroseconds(150);  lcdNibble(0x3);  delayMicroseconds(150);  lcdNibble(0x2);  delayMicroseconds(150);  lcdSend(0x28, false);  // 2 lines of text  lcdSend(0x0C, false);  // screen on, no cursor  lcdSend(0x06, false);  // move right after each letter}void lcdNibble(byte bits) {  for (byte i = 0; i < 4; i++) digitalWrite(LCD_DATA[i], (bits >> i) & 1);  digitalWrite(LCD_E, HIGH);  delayMicroseconds(1);  digitalWrite(LCD_E, LOW);  delayMicroseconds(100);}void lcdSend(byte value, bool isLetter) {  digitalWrite(LCD_RS, isLetter ? HIGH : LOW);  lcdNibble(value >> 4);  lcdNibble(value & 0x0F);}void lcdPrintAt(byte column, byte row, const char *text) {  lcdSend(0x80 | (column + (row ? 0x40 : 0)), false);  while (*text) lcdSend(*text++, true);}