Unit E - College Practice

26. Capstone 2: Clock, Alarm & Servo

Build a timed actuator system without blocking delays.

Estimated time 6-8 hours

Learning outcomes

Share I2C between RTC and LCD
Compare RTC time to an alarm setting
Drive a servo and buzzer safely
Implement alarm states and acknowledgment

Parts and preparation

Uno, DS1307 RTC, I2C LCD, servo with external supply, buzzer and button. Install the same libraries as lessons 13, 17 and 19.

Before power: inspect wiring, confirm supply voltage and ensure all connected circuits share GND.

Libraries for this lesson

In Arduino IDE 2 open Tools → Manage Libraries…. Search by the Library Manager name and install the package by the exact author below. Similar names from other authors can use different APIs and will break the example.

Include	Library Manager name	Author	Install note
`Wire.h`	Wire	Arduino	Built into the Arduino core. No Library Manager install required.
`RTClib.h`	RTClib	Adafruit	Same package as lesson 19. Install via Library Manager.
`Servo.h`	Servo	Arduino	Built-in with Arduino AVR Boards. No Library Manager install required.
`LiquidCrystal_I2C.h`	LiquidCrystal I2C	Frank de Brabander	Needed if you add the I2C LCD display. Same package as lesson 17.

Open the diagram for a larger view. Trace every connection before building.

Shared bus

The RTC and LCD coexist on SDA/SCL because their I2C addresses differ.

State design

Normal, alarming and acknowledged states make behavior explicit. The button changes state; time and timers update outputs.

Actuator safety

Servo power is separate and grounds are common. The mechanism must not bind at end positions.

Acceptance test

Verify display time, trigger time, buzzer, servo movement, acknowledge button and power-cycle clock retention.

Wiring and safe build sequence

RTC and LCD share A4/SDA, A5/SCL, 5 V and GND
Servo signal -> D9; servo external supply GND -> Uno GND
Buzzer -> D6
Acknowledge button D2 -> GND with INPUT_PULLUP

Power rule: switch off before moving wires. Arduino I/O pins are control signals; high-current loads require a driver and suitable external supply.

Worked sketch

Download .ino sketch

#include <Wire.h>
#include <RTClib.h>
#include <Servo.h>

RTC_DS1307 rtc;
Servo latch;
bool acknowledged = false;

void setup() {
  rtc.begin();
  latch.attach(9);
  pinMode(2, INPUT_PULLUP);
  pinMode(6, OUTPUT);
}

void loop() {
  DateTime now = rtc.now();
  bool alarmTime = now.hour() == 8 && now.minute() == 0;
  if (digitalRead(2) == LOW) acknowledged = true;
  if (!alarmTime) acknowledged = false;

  if (alarmTime && !acknowledged) {
    latch.write(90);
    tone(6, 1200);
  } else {
    latch.write(10);
    noTone(6);
  }
}

How the code works

The example focuses on alarm state; add the LCD output from lesson 19.
Acknowledgment resets after the alarm minute ends.

Test and record evidence

Expected result: At the configured time the servo moves and buzzer sounds until acknowledged.

Practical evidence checklist

Labelled wiring or block diagram Uploaded sketch and observed result At least one measured/tested value Fault or improvement recorded in logbook

Common faults and checks

Test with an alarm a minute ahead.
Confirm the RTC was set and retains time.
Power the servo separately.

Extension challenge: Allow alarm hour/minute adjustment with two debounced buttons and store settings in EEPROM.

Check your understanding

Q1. Why can RTC and LCD share I2C wires?

Show answer

They have different bus addresses.

Q2. What is the purpose of an acknowledged state?

Show answer

It records that the user silenced the current alarm event.