{"id":52356,"date":"2026-11-01T10:51:00","date_gmt":"2026-11-01T10:51:00","guid":{"rendered":"http:\/\/siratek.net\/index.php\/tutorials\/smart-alarm-clock\/"},"modified":"2026-11-01T10:51:00","modified_gmt":"2026-11-01T10:51:00","slug":"smart-alarm-clock","status":"publish","type":"siratek_tutorial","link":"https:\/\/siratek.net\/index.php\/tutorials\/smart-alarm-clock\/","title":{"rendered":"Project, a Smart Alarm Clock"},"content":{"rendered":"

<\/p>\n

What you will build<\/h2>\n

A clock that shows the time on a 16\u00d72 display, lets you set an alarm with buttons, and wakes you with a tune. Press to snooze, hold to stop.<\/p>\n

It is the most interactive project in the library, and that is what it teaches. The others read sensors and report; this one has to listen to a person<\/strong>, which means a menu, buttons that behave differently on a press and a hold, and a display that shows the right thing at the right time.<\/p>\n

Before you begin<\/h2>\n

Parts<\/h3>\n\n\n\n\n\n\n\n\n\n\n
Part<\/th>\nSiratek product<\/th>\nIts own tutorial<\/th>\n<\/tr>\n<\/thead>\n
Arduino Uno<\/td>\n2219<\/td>\nGetting Started with Arduino Uno<\/em><\/td>\n<\/tr>\n
16\u00d72 LCD with I2C backpack<\/td>\n2484<\/td>\nA 16\u00d72 LCD over I2C<\/em><\/td>\n<\/tr>\n
DS3231 real time clock<\/td>\n2522<\/td>\nKeeping Time with a DS3231<\/em><\/td>\n<\/tr>\n
Passive buzzer<\/td>\n8051<\/td>\nPlay Tones with a Passive Buzzer<\/em><\/td>\n<\/tr>\n
Three tactile push buttons<\/td>\n49488<\/td>\nRead a Push Button<\/em><\/td>\n<\/tr>\n
Breadboard and jumper wires<\/td>\n<\/td>\nUsing a Breadboard<\/em><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Three buttons: Mode<\/strong>, Up<\/strong> and Down<\/strong>. All three wired to ground with INPUT_PULLUP<\/code>, so no resistors are needed.<\/p>\n

Two addresses on one bus<\/h3>\n

The display and the clock both sit on A4<\/code> and A5<\/code>. The display\u2019s backpack answers at 0x27 or 0x3F<\/strong>, and the clock at 0x68<\/strong>, so they do not clash.<\/p>\n

Run the bus scanner first and note which address your backpack uses. A 16\u00d72 LCD over I2C<\/em> explains why it is a coin toss and why copying 0x27<\/code> from a tutorial is a poor idea.<\/p>\n

Buttons are the hard part, not the clock<\/h3>\n

This is worth saying before you start, because it shapes the whole sketch.<\/p>\n

Reading a button is trivial. Making three buttons feel right is not, and a clock that is annoying to set is a clock nobody sets. Three behaviours are needed:<\/p>\n

    \n
  • A press<\/strong>: a single, debounced action. Used for Mode, and for snooze.<\/li>\n
  • A repeat<\/strong>: hold Up and the minutes should keep climbing, slowly at first then faster. Otherwise setting an alarm for 06:45 means forty-five separate presses.<\/li>\n
  • A long hold<\/strong>: distinct from a press. Used to stop the alarm, so a sleepy hand cannot cancel it by accident.<\/li>\n<\/ul>\n

    All three come from one small piece of code, below, and that piece is the most reusable thing in this project.<\/p>\n

    How it works<\/h2>\n

    Modes<\/h3>\n

    The clock is always in exactly one mode, and Mode cycles between them:<\/p>\n\n\n\n\n\n\n\n\n
    Mode<\/th>\nShows<\/th>\nUp and Down<\/th>\n<\/tr>\n<\/thead>\n
    SHOW_TIME<\/code><\/td>\nTime, date, alarm<\/td>\nNothing<\/td>\n<\/tr>\n
    SET_ALARM_HOUR<\/code><\/td>\nAlarm, hour flashing<\/td>\nChange the hour<\/td>\n<\/tr>\n
    SET_ALARM_MINUTE<\/code><\/td>\nAlarm, minute flashing<\/td>\nChange the minute<\/td>\n<\/tr>\n
    SET_ALARM_ONOFF<\/code><\/td>\nAlarm on or off<\/td>\nToggle it<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    Pressing Mode from the last one returns to SHOW_TIME<\/code> and saves. The same state-machine idea as the pedestrian crossing, with a person driving the transitions instead of a timer.<\/p>\n

    Ringing<\/h3>\n

    When the alarm time arrives and the alarm is on, the clock enters a ringing state:<\/p>\n

      \n
    • Press any button<\/strong>: snooze for nine minutes.<\/li>\n
    • Hold Mode for two seconds<\/strong>: stop until tomorrow.<\/li>\n
    • After ten minutes<\/strong> with no response: give up, so a clock in an empty house does not sound all day.<\/li>\n<\/ul>\n

      The alarm fires on a minute match<\/strong>, and the sketch records which minute it fired in so it does not fire again within the same minute.<\/p>\n

      Remembering the alarm<\/h3>\n

      The alarm setting is kept in the Uno\u2019s EEPROM<\/strong>, so it survives power being removed. Without that, every power cut loses the setting, which for a clock is most of the point.<\/p>\n

      EEPROM has a finite write endurance, around a hundred thousand writes per location, so the sketch writes only when the setting changes<\/strong>, not on every loop. Writing in loop()<\/code> would use that up in a day.<\/p>\n

      Pin reference<\/h2>\n\n\n\n\n\n\n\n\n\n\n\n\n\n
      Device<\/th>\nPin<\/th>\nConnect to<\/th>\n<\/tr>\n<\/thead>\n
      LCD backpack<\/td>\nGND<\/code>, VCC<\/code><\/td>\nUno GND<\/code>, 5V<\/code><\/td>\n<\/tr>\n
      LCD backpack<\/td>\nSDA<\/code>, SCL<\/code><\/td>\nUno A4<\/code>, A5<\/code><\/td>\n<\/tr>\n
      DS3231<\/td>\nGND<\/code>, VCC<\/code><\/td>\nUno GND<\/code>, 5V<\/code><\/td>\n<\/tr>\n
      DS3231<\/td>\nSDA<\/code>, SCL<\/code><\/td>\nUno A4<\/code>, A5<\/code><\/td>\n<\/tr>\n
      Buzzer<\/td>\n+<\/code><\/td>\nUno D9<\/code><\/td>\n<\/tr>\n
      Buzzer<\/td>\n-<\/code><\/td>\nUno GND<\/code><\/td>\n<\/tr>\n
      Mode button<\/td>\n<\/td>\nUno D2<\/code> to GND<\/code><\/td>\n<\/tr>\n
      Up button<\/td>\n<\/td>\nUno D3<\/code> to GND<\/code><\/td>\n<\/tr>\n
      Down button<\/td>\n<\/td>\nUno D4<\/code> to GND<\/code><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
      \"A
      Two I2C devices at different addresses, three buttons using the internal pull-ups, and one buzzer.<\/figcaption><\/figure>\n

      Build it in stages<\/h2>\n

      Stage 1: scan, then show the time<\/h3>\n

      Run the bus scanner and note both addresses. Then put the time on the display, with no buttons and no alarm. That alone is a working clock and proves the two hardest parts.<\/p>\n

      Leave it running while you build the rest.<\/p>\n

      Stage 2: one button, printing to serial<\/h3>\n

      Get the button helper below working with the Mode button and Serial.print()<\/code>. Check that a press reports once, a hold repeats, and a long hold reports separately.<\/p>\n

      Do this before touching the display.<\/strong> Button behaviour is fiddly, and debugging it through a 16-character screen is miserable.<\/p>\n

      Stage 3: the modes<\/h3>\n

      Add Up and Down, and the four modes, still printing to serial. Then put the modes on the display.<\/p>\n

      Stage 4: the alarm<\/h3>\n

      Add the buzzer, the ringing state and the EEPROM. The complete sketch below.<\/p>\n

      The complete sketch<\/h2>\n
      \/\/ Siratek: a smart alarm clock.\n\/\/ LCD and DS3231 share I2C; three buttons to ground; a passive buzzer.\n\n#include <Wire.h>\n#include <LiquidCrystal_I2C.h>\n#include <RTClib.h>\n#include <EEPROM.h>\n\n\/\/ Use the address your scanner printed.\nLiquidCrystal_I2C lcd(0x27, 16, 2);\nRTC_DS3231 rtc;\n\nconst int buzzerPin = 9;\nconst int MODE_BTN = 2, UP_BTN = 3, DOWN_BTN = 4;\n\nconst int EEPROM_HOUR = 0, EEPROM_MINUTE = 1, EEPROM_ON = 2, EEPROM_MAGIC = 3;\nconst byte MAGIC = 0x5A;          \/\/ says \"these bytes are ours\"\n\nenum Mode { SHOW_TIME, SET_ALARM_HOUR, SET_ALARM_MINUTE, SET_ALARM_ONOFF };\nMode mode = SHOW_TIME;\n\nbyte alarmHour = 7, alarmMinute = 0;\nbool alarmOn = false;\nbool settingChanged = false;\n\nbool ringing = false;\nunsigned long ringingSince = 0;\nint firedInMinute = -1;           \/\/ so it fires once per minute, not repeatedly\n\nunsigned long lastDraw = 0;\n\n\/\/ ---------------------------------------------------------------- buttons\n\nstruct Button {\n  byte pin;\n  bool stable;                    \/\/ debounced level, true when pressed\n  unsigned long changedAt;\n  unsigned long pressedAt;\n  unsigned long lastRepeat;\n  bool longFired;\n};\n\nButton buttons[3];\n\nvoid setupButton(Button& b, byte pin) {\n  pinMode(pin, INPUT_PULLUP);\n  b.pin = pin;\n  b.stable = false;\n  b.changedAt = b.pressedAt = b.lastRepeat = 0;\n  b.longFired = false;\n}\n\n\/\/ Returns: 0 nothing, 1 a press, 2 a repeat, 3 a long hold.\nbyte pollButton(Button& b) {\n  bool now = (digitalRead(b.pin) == LOW);\n\n  if (now != b.stable) {\n    if (millis() - b.changedAt < 30) {\n      return 0;                   \/\/ still bouncing\n    }\n    b.changedAt = millis();\n    b.stable = now;\n\n    if (now) {\n      b.pressedAt = millis();\n      b.lastRepeat = millis();\n      b.longFired = false;\n      return 1;                   \/\/ the moment of the press\n    }\n    return 0;                     \/\/ release\n  }\n\n  if (!b.stable) {\n    return 0;\n  }\n\n  unsigned long held = millis() - b.pressedAt;\n\n  if (held > 2000 && !b.longFired) {\n    b.longFired = true;\n    return 3;\n  }\n\n  \/\/ Repeat while held: slow at first, then faster.\n  if (held > 600) {\n    unsigned long gap = (held > 3000) ? 80 : 250;\n    if (millis() - b.lastRepeat >= gap) {\n      b.lastRepeat = millis();\n      return 2;\n    }\n  }\n\n  return 0;\n}\n\n\/\/ ---------------------------------------------------------------- storage\n\nvoid loadAlarm() {\n  if (EEPROM.read(EEPROM_MAGIC) != MAGIC) {\n    \/\/ First run on this board: EEPROM holds whatever it held.\n    saveAlarm();\n    return;\n  }\n  alarmHour = EEPROM.read(EEPROM_HOUR);\n  alarmMinute = EEPROM.read(EEPROM_MINUTE);\n  alarmOn = EEPROM.read(EEPROM_ON) != 0;\n\n  if (alarmHour > 23) alarmHour = 7;\n  if (alarmMinute > 59) alarmMinute = 0;\n}\n\nvoid saveAlarm() {\n  \/\/ EEPROM.update writes only if the value differs, which saves the endurance.\n  EEPROM.update(EEPROM_HOUR, alarmHour);\n  EEPROM.update(EEPROM_MINUTE, alarmMinute);\n  EEPROM.update(EEPROM_ON, alarmOn ? 1 : 0);\n  EEPROM.update(EEPROM_MAGIC, MAGIC);\n}\n\n\/\/ ---------------------------------------------------------------- display\n\nvoid two(byte v) {\n  if (v < 10) lcd.print('0');\n  lcd.print(v);\n}\n\nvoid draw() {\n  DateTime now = rtc.now();\n\n  lcd.setCursor(0, 0);\n  if (ringing) {\n    lcd.print(F(\"** ALARM **     \"));\n  } else {\n    two(now.hour()); lcd.print(':');\n    two(now.minute()); lcd.print(':');\n    two(now.second());\n    lcd.print(F(\"   \"));\n    two(now.day()); lcd.print('\/');\n    two(now.month());\n  }\n\n  lcd.setCursor(0, 1);\n  switch (mode) {\n    case SHOW_TIME:\n      lcd.print(F(\"Alarm \"));\n      two(alarmHour); lcd.print(':'); two(alarmMinute);\n      lcd.print(alarmOn ? F(\" on \") : F(\" off\"));\n      lcd.print(F(\"   \"));\n      break;\n    case SET_ALARM_HOUR:\n      lcd.print(F(\"Set hour   \"));\n      two(alarmHour); lcd.print(':'); two(alarmMinute);\n      break;\n    case SET_ALARM_MINUTE:\n      lcd.print(F(\"Set minute \"));\n      two(alarmHour); lcd.print(':'); two(alarmMinute);\n      break;\n    case SET_ALARM_ONOFF:\n      lcd.print(alarmOn ? F(\"Alarm: on       \") : F(\"Alarm: off      \"));\n      break;\n  }\n}\n\n\/\/ ------------------------------------------------------------------ alarm\n\nconst int melody[] = {880, 988, 1047, 988};\nint melodyStep = 0;\nunsigned long lastNote = 0;\n\nvoid ringTune() {\n  if (millis() - lastNote >= 350) {\n    lastNote = millis();\n    tone(buzzerPin, melody[melodyStep], 200);\n    melodyStep = (melodyStep + 1) % 4;\n  }\n}\n\nvoid startRinging() {\n  ringing = true;\n  ringingSince = millis();\n  melodyStep = 0;\n}\n\nvoid stopRinging() {\n  ringing = false;\n  noTone(buzzerPin);\n}\n\nvoid snooze() {\n  stopRinging();\n  \/\/ Nine minutes on, as alarm clocks have always done.\n  alarmMinute = (alarmMinute + 9) % 60;\n  if (alarmMinute < 9) {\n    alarmHour = (alarmHour + 1) % 24;\n  }\n  firedInMinute = -1;\n  settingChanged = true;\n}\n\n\/\/ ------------------------------------------------------------------- main\n\nvoid setup() {\n  Serial.begin(9600);\n\n  lcd.init();\n  lcd.backlight();\n  lcd.setCursor(0, 0);\n  lcd.print(F(\"Siratek clock\"));\n\n  if (!rtc.begin()) {\n    lcd.setCursor(0, 1);\n    lcd.print(F(\"No clock found\"));\n    while (1) { delay(100); }\n  }\n  if (rtc.lostPower()) {\n    rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));\n  }\n\n  setupButton(buttons[0], MODE_BTN);\n  setupButton(buttons[1], UP_BTN);\n  setupButton(buttons[2], DOWN_BTN);\n\n  pinMode(buzzerPin, OUTPUT);\n  loadAlarm();\n\n  delay(800);\n  lcd.clear();\n}\n\nvoid adjust(int delta) {\n  switch (mode) {\n    case SET_ALARM_HOUR:\n      alarmHour = (alarmHour + 24 + delta) % 24;\n      settingChanged = true;\n      break;\n    case SET_ALARM_MINUTE:\n      alarmMinute = (alarmMinute + 60 + delta) % 60;\n      settingChanged = true;\n      break;\n    case SET_ALARM_ONOFF:\n      alarmOn = !alarmOn;\n      settingChanged = true;\n      break;\n    default:\n      break;\n  }\n}\n\nvoid loop() {\n  byte modeEvent = pollButton(buttons[0]);\n  byte upEvent   = pollButton(buttons[1]);\n  byte downEvent = pollButton(buttons[2]);\n\n  if (ringing) {\n    ringTune();\n\n    if (modeEvent == 3) {                  \/\/ held: stop until tomorrow\n      stopRinging();\n    } else if (modeEvent == 1 || upEvent == 1 || downEvent == 1) {\n      snooze();\n    } else if (millis() - ringingSince > 600000UL) {\n      stopRinging();                       \/\/ give up after ten minutes\n    }\n  } else {\n    if (modeEvent == 1) {\n      mode = (Mode) ((mode + 1) % 4);\n      if (mode == SHOW_TIME && settingChanged) {\n        saveAlarm();\n        settingChanged = false;\n      }\n      lcd.clear();\n    }\n\n    if (upEvent == 1 || upEvent == 2)   adjust(+1);\n    if (downEvent == 1 || downEvent == 2) adjust(-1);\n\n    DateTime now = rtc.now();\n    if (alarmOn\n        && now.hour() == alarmHour\n        && now.minute() == alarmMinute\n        && firedInMinute != now.minute()) {\n      firedInMinute = now.minute();\n      startRinging();\n      lcd.clear();\n    }\n  }\n\n  \/\/ Redraw four times a second, not every pass.\n  if (millis() - lastDraw >= 250) {\n    lastDraw = millis();\n    draw();\n  }\n}<\/code><\/pre>\n
      The three decisions that matter most<\/h3>\n
      pollButton()<\/code> returns an event, not a state.<\/strong> One function, three behaviours, and the rest of the sketch reads as \u201cif the Mode button was pressed\u201d rather than fiddling with timestamps. It is the most reusable thing here; lift it into your next project.<\/p>\n
      EEPROM.update()<\/code>, not EEPROM.write()<\/code>.<\/strong> update()<\/code> reads first and writes only if the value differs. On a clock that saves whenever a setting changes, that is the difference between using a handful of the EEPROM\u2019s hundred thousand writes and using them all.<\/p>\n
      The display is redrawn four times a second<\/strong>, not every pass of loop()<\/code>. The LCD is slow, and redrawing it constantly makes the buttons feel unresponsive because the loop spends its time talking to the screen.<\/p>\n
      Testing it<\/h2>\n\n\n\n\n\n\n\n\n\n\n\n\n
      Try this<\/th>\nIt should<\/th>\n<\/tr>\n<\/thead>\n
      Watch the seconds<\/td>\nAdvance steadily, no stutter<\/td>\n<\/tr>\n
      Press Mode four times<\/td>\nCycle the modes and return to the time<\/td>\n<\/tr>\n
      Hold Up in minute mode<\/td>\nClimb slowly, then speed up after a few seconds<\/td>\n<\/tr>\n
      Set an alarm a minute ahead<\/td>\nRing at the right moment<\/td>\n<\/tr>\n
      Press any button while ringing<\/td>\nSnooze; it rings again nine minutes later<\/td>\n<\/tr>\n
      Hold Mode while ringing<\/td>\nStop, and not ring again today<\/td>\n<\/tr>\n
      Set an alarm, unplug, plug back in<\/td>\nKeep the alarm setting and the time<\/td>\n<\/tr>\n
      Leave it ringing<\/td>\nGive up after ten minutes<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
      The seventh is the one that proves the EEPROM and the clock battery are both doing their jobs, and it is the reason this is a clock rather than a demonstration.<\/p>\n
      Making it yours<\/h2>\n
        \n
      • A light that comes on before the alarm.<\/strong> An LED or a relay, switched fifteen minutes early and brightened with PWM. Waking to light is pleasanter than waking to sound.<\/li>\n
      • Temperature on the display.<\/strong> The DS3231 measures its own, free: rtc.getTemperature()<\/code>. It reads a little high, which Keeping Time with a DS3231<\/em> explains.<\/li>\n
      • A proper tune.<\/strong> The melody here is four notes. Play Tones with a Passive Buzzer<\/em> has the note tables.<\/li>\n
      • Dim the backlight at night.<\/strong> The backpack\u2019s backlight jumper can be replaced with a transistor on a PWM pin.<\/li>\n
      • Set the time from the buttons.<\/strong> The sketch sets the alarm but not the clock. Two more modes and the same adjust()<\/code> pattern, and you no longer need to recompile to correct it.<\/li>\n<\/ul>\n
        That last one is a genuinely good exercise, because it reuses everything already here.<\/p>\n
        Troubleshooting<\/h2>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
        Symptom<\/th>\nLikely cause<\/th>\nCheck or fix<\/th>\n<\/tr>\n<\/thead>\n
        Display blank, backlight on<\/td>\nContrast<\/td>\nTurn the blue trimmer through its range<\/td>\n<\/tr>\n
        Nothing found on the bus<\/td>\nSDA<\/code> and SCL<\/code> swapped<\/td>\nSDA<\/code> is A4<\/code>, SCL<\/code> is A5<\/code><\/td>\n<\/tr>\n
        Display works, clock not found<\/td>\nAddress, or the coin cell<\/td>\nScan; expect 0x68<\/td>\n<\/tr>\n
        Time resets on every power-up<\/td>\nadjust()<\/code> unconditional<\/td>\nGuard it with lostPower()<\/code><\/td>\n<\/tr>\n
        Alarm lost on power-up<\/td>\nNot saved to EEPROM<\/td>\nsaveAlarm()<\/code> when leaving the menus<\/td>\n<\/tr>\n
        Buttons feel sluggish<\/td>\nDisplay redrawn every pass<\/td>\nRedraw four times a second<\/td>\n<\/tr>\n
        One press changes the hour twice<\/td>\nNot debounced<\/td>\nCheck the 30 ms guard<\/td>\n<\/tr>\n
        Hold does not repeat<\/td>\nRepeat branch not reached<\/td>\nIt starts after 600 ms<\/td>\n<\/tr>\n
        Alarm rings repeatedly in one minute<\/td>\nfiredInMinute<\/code> not set<\/td>\nIt is set when ringing starts<\/td>\n<\/tr>\n
        Buzzer silent<\/td>\nActive buzzer, not passive<\/td>\ntone()<\/code> needs a passive one<\/td>\n<\/tr>\n
        Snooze sets a strange time<\/td>\nHour not carried<\/td>\nThe % 60<\/code> wrap needs the hour bump<\/td>\n<\/tr>\n
        Display garbled after hours<\/td>\nNoise on a long I2C run<\/td>\nShorten the leads<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
        Sources and attribution<\/h2>\n
        All text, wiring guidance and code in this project are original Siratek work.<\/p>\n
          \n
        • Component behaviour is as described in A 16\u00d72 LCD over I2C<\/em>, Keeping Time with a DS3231<\/em>, Play Tones with a Passive Buzzer<\/em> and Read a Push Button<\/em>, including the backpack\u2019s variable address, the lostPower()<\/code> behaviour and the tone()<\/code> timer conflict.<\/li>\n
        • EEPROM write endurance is from the ATmega328P datasheet.<\/li>\n<\/ul>\n
          The nine-minute snooze is the long-standing convention rather than anything required. No third-party tutorial text, diagrams, photographs or code has been reproduced here.<\/p>\n
          <\/p>\n<\/body>","protected":false},"excerpt":{"rendered":"
          A clock that shows the time on a 16×2 display, lets you set an alarm with buttons, and wakes you with a tune. Press to snooze, hold to stop.<\/p>\n","protected":false},"featured_media":0,"template":"","siratek_tutorial_level":[],"class_list":["post-52356","siratek_tutorial","type-siratek_tutorial","status-publish","hentry"],"yoast_head":"\nProject, a Smart Alarm Clock - siratek<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"http:\/\/siratek.net\/index.php\/tutorials\/smart-alarm-clock\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Project, a Smart Alarm Clock - siratek\" \/>\n<meta property=\"og:description\" content=\"A clock that shows the time on a 16x2 display, lets you set an alarm with buttons, and wakes you with a tune. 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