Alarm clock with a timer on a four-digit display, on an Arduino Uno

// Alarm clock with a kitchen timer, a calendar and a thermometer, all on one
// four-digit display.
//
//   74HC595 DS -> pin 8    SHCP -> pin 13    STCP -> pin 12
//   Q0 to Q7 -> segments a to g and the dot; digit commons -> pins 2, 4, A3, 7
//   buttons, each to GND (INPUT_PULLUP): "+" -> A0, "set" -> A1,
//   "++" -> A2, "view" -> pin 10
//   DS1307 clock SDA -> A4, SCL -> A5     DHT11 DATA -> pin 11
//   active buzzer -> pin 3     RGB LED red -> pin 6, green -> pin 9
//
// The display shows the time. "view" steps through the year, the month and
// day, the temperature (ending in C) and the humidity (ending in H), and
// after five seconds it comes back to the time.
//
// Timer: press "+" for a minute or "++" for a second, then "set" to start.
// "set" again cancels it.
//
// Alarm: on the time, with no timer set, press "set". The display shows the
// alarm time; "+" adds an hour, "++" a minute, and "set" saves it. It is kept
// in the EEPROM, so it survives a power cut. The RGB LED is yellow while an
// alarm is set and green when none is. To turn the alarm off, set it to
// 00:00.
//
// When the timer runs out or the alarm time comes, the buzzer beeps and the
// LED flashes red and green until you press "set".

#include <Wire.h>
#include <RTClib.h>
#include <DHT.h>
#include <EEPROM.h>

const int DATA_PIN = 8;
const int LATCH_PIN = 12;
const int CLOCK_PIN = 13;
const int DIGIT_PINS[4] = {2, 4, A3, 7};
const int BUZZER = 3;
const int RED_PIN = 6;
const int GREEN_PIN = 9;

RTC_DS1307 rtc;
DHT dht(11, DHT11);

//                       gfedcba
const byte NUMBERS[10] = {0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F};
const byte LETTER_C = 0x39;
const byte LETTER_H = 0x76;
const byte DOT = 0x80;

struct Button {
  int pin;
  bool down;
  unsigned long changedAt;
};
Button plus = {A0, false, 0};
Button setKey = {A1, false, 0};
Button plusPlus = {A2, false, 0};
Button view = {10, false, 0};

enum Mode { CLOCK, TIMER_SET, TIMER_RUN, ALARM_SET, RINGING };
Mode mode = CLOCK;
int page = 0;  // 0 time, 1 year, 2 month and day, 3 temperature, 4 humidity
unsigned long pageAt = 0;
long timerLeft = 0;  // seconds
unsigned long lastTick = 0;
int alarmMinutes = 0;  // minutes after midnight; 0 is no alarm
int lastRungMinute = -1;
byte shown[4];
int digit = 0;
float temperature = 0;
float humidity = 0;
unsigned long lastReading = 0;

bool pressed(Button &b) {
  bool now = digitalRead(b.pin) == LOW;
  if (now != b.down && millis() - b.changedAt > 30) {
    b.down = now;
    b.changedAt = millis();
    return now;
  }
  return false;
}

void color(int r, int g) {
  analogWrite(RED_PIN, r);
  analogWrite(GREEN_PIN, g);
}

void restingColor() {
  if (alarmMinutes > 0) color(160, 100);
  else color(0, 160);
}

void showNumber(int value, bool colon) {
  shown[0] = NUMBERS[value / 1000 % 10];
  shown[1] = NUMBERS[value / 100 % 10] | (colon ? DOT : 0);
  shown[2] = NUMBERS[value / 10 % 10];
  shown[3] = NUMBERS[value % 10];
}

void showReading(int value, byte letter) {
  shown[0] = 0;
  shown[1] = NUMBERS[value / 10 % 10];
  shown[2] = NUMBERS[value % 10];
  shown[3] = letter;
}

void refresh() {
  for (int i = 0; i < 4; i++) digitalWrite(DIGIT_PINS[i], HIGH);
  digitalWrite(LATCH_PIN, LOW);
  shiftOut(DATA_PIN, CLOCK_PIN, MSBFIRST, shown[digit]);
  digitalWrite(LATCH_PIN, HIGH);
  digitalWrite(DIGIT_PINS[digit], LOW);
  digit = (digit + 1) % 4;
}

void saveAlarm() {
  EEPROM.put(0, alarmMinutes);
  Serial.print("alarm saved: ");
  Serial.println(alarmMinutes > 0 ? alarmMinutes : 0);
}

void startRinging(const char *why) {
  mode = RINGING;
  Serial.println(why);
}

void updateDisplay(const DateTime &now) {
  switch (mode) {
    case TIMER_SET:
    case TIMER_RUN:
      showNumber(timerLeft / 60 * 100 + timerLeft % 60, true);
      return;
    case ALARM_SET:
      showNumber(alarmMinutes / 60 * 100 + alarmMinutes % 60, true);
      return;
    default:
      break;
  }
  if (page == 1) showNumber(now.year(), false);
  else if (page == 2) showNumber(now.month() * 100 + now.day(), true);
  else if (page == 3) showReading((int)temperature, LETTER_C);
  else if (page == 4) showReading((int)humidity, LETTER_H);
  else showNumber(now.hour() * 100 + now.minute(), now.second() % 2 == 0);
}

void setup() {
  pinMode(DATA_PIN, OUTPUT);
  pinMode(LATCH_PIN, OUTPUT);
  pinMode(CLOCK_PIN, OUTPUT);
  for (int i = 0; i < 4; i++) pinMode(DIGIT_PINS[i], OUTPUT);
  pinMode(plus.pin, INPUT_PULLUP);
  pinMode(setKey.pin, INPUT_PULLUP);
  pinMode(plusPlus.pin, INPUT_PULLUP);
  pinMode(view.pin, INPUT_PULLUP);
  pinMode(BUZZER, OUTPUT);
  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: alarm clock. view (10), + (A0), ++ (A2), set (A1).");
  if (!rtc.begin()) Serial.println("no clock found: check SDA and SCL");
  if (!rtc.isrunning()) rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  dht.begin();
  EEPROM.get(0, alarmMinutes);
  if (alarmMinutes < 0 || alarmMinutes >= 24 * 60) alarmMinutes = 0;  // a fresh EEPROM reads 0xFF
  restingColor();
}

void loop() {
  DateTime now = rtc.now();
  bool p = pressed(plus);
  bool s = pressed(setKey);
  bool pp = pressed(plusPlus);
  bool v = pressed(view);

  if (millis() - lastReading > 2000) {
    lastReading = millis();
    float t = dht.readTemperature();
    float h = dht.readHumidity();
    if (!isnan(t)) temperature = t;
    if (!isnan(h)) humidity = h;
  }

  switch (mode) {
    case CLOCK:
      if (v) {
        page = (page + 1) % 5;
        pageAt = millis();
      }
      if (page != 0 && millis() - pageAt > 5000) page = 0;
      if (p || pp) {
        mode = TIMER_SET;
        timerLeft = p ? 60 : 1;
        Serial.println("timer: set it, then press set");
      } else if (s) {
        mode = ALARM_SET;
        color(160, 100);
        Serial.println("alarm: set the time, then press set");
      }
      break;
    case TIMER_SET:
      if (p && timerLeft < 99L * 60) timerLeft += 60;
      if (pp && timerLeft < 99L * 60 + 59) timerLeft += 1;
      if (s) {
        mode = TIMER_RUN;
        lastTick = millis();
        Serial.println("timer started");
      }
      break;
    case TIMER_RUN:
      if (s) {
        mode = CLOCK;
        Serial.println("timer cancelled");
      } else if (millis() - lastTick >= 1000) {
        lastTick += 1000;
        if (--timerLeft <= 0) startRinging("time is up");
      }
      break;
    case ALARM_SET:
      if (p) alarmMinutes = (alarmMinutes + 60) % (24 * 60);
      if (pp) alarmMinutes = alarmMinutes / 60 * 60 + (alarmMinutes % 60 + 1) % 60;
      if (s) {
        saveAlarm();
        mode = CLOCK;
        restingColor();
      }
      break;
    case RINGING: {
      bool on = (millis() / 250) % 2 == 0;
      digitalWrite(BUZZER, on ? HIGH : LOW);
      color(on ? 160 : 0, on ? 0 : 160);
      if (s) {
        digitalWrite(BUZZER, LOW);
        mode = CLOCK;
        restingColor();
        Serial.println("quiet");
      }
      break;
    }
  }

  int minuteOfDay = now.hour() * 60 + now.minute();
  if (mode == CLOCK && alarmMinutes > 0 && minuteOfDay == alarmMinutes && lastRungMinute != minuteOfDay) {
    lastRungMinute = minuteOfDay;
    startRinging("alarm!");
  }

  updateDisplay(now);
  refresh();
  delay(3);
}