Learning Objectives

• Integrate concepts from Units 1–8 into a single working embedded device.
• Independently plan, wire, code, test and debug a small project.
• Present and demonstrate the finished project to trainers and peers.

9.1 Project Development Cycle

1. Define the problem and requirements.
2. Select the project option and components.
3. Draw a block diagram.
4. Prepare a component and pin list.
5. Build and inspect the circuit before applying power.
6. Write firmware in small, testable stages.
7. Test each part and use the Serial Monitor for debugging.
8. Add an interrupt or non-blocking timing element; where feasible, use a FreeRTOS task.
9. Document the final design, fault encountered and solution.
10. Prepare a 3-minute demonstration.

9.2 Capstone Option A: Reaction-Time Reflex Tester

The module proposes a reaction-time tester using an LED, a button and millis()-based timing. A simple sequence is: start a test, turn on the LED, detect the response, calculate elapsed time and report the result.

Figure 9.1: Original example circuit for the reflex-timer project.

Suggested Pin/Component Table

Component	Example connection	Purpose
LED + 220 Ω resistor	D8 → resistor → LED → GND	Visual start signal
Push button	D2 → button → GND; INPUT_PULLUP	User response
USB/board	USB to computer	Power, programming and Serial Monitor

Example Reflex-Timer Program

const byte LED_PIN = 8;
const byte BUTTON_PIN = 2;

bool testRunning = false;
unsigned long startTime = 0;

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  Serial.begin(9600);
  Serial.println(“Reflex Timer”);
}

void loop() {
  if (!testRunning && digitalRead(BUTTON_PIN) == LOW) {
    delay(200);
    while (digitalRead(BUTTON_PIN) == LOW) {}

    Serial.println(“Get ready…”);
    delay(1000);

    digitalWrite(LED_PIN, HIGH);
    startTime = millis();
    testRunning = true;
  }

  if (testRunning && digitalRead(BUTTON_PIN) == LOW) {
    unsigned long reactionTime = millis() – startTime;
    digitalWrite(LED_PIN, LOW);

    Serial.print(“Reaction time: “);
    Serial.print(reactionTime);
    Serial.println(” ms”);

    testRunning = false;
    delay(300);
  }
}

Improvement task: the module emphasizes millis()-based timing. After making the basic version work, trainees can improve the debounce logic so the program uses less blocking code.

9.3 Capstone Option B: Environment Alarm

The module proposes an environment alarm using an LDR or DHT sensor. When the measured condition crosses a selected threshold, the system activates a buzzer/LED and displays information on an I2C LCD.

Figure 9.2: Original example block/circuit diagram for the environment-alarm project.

Example LDR Alarm Logic

• Read the LDR voltage-divider value using analogRead().
• Choose and document a threshold from observed laboratory readings.
• Compare the sensor value with the threshold.
• Activate the buzzer and/or LED when the selected condition is reached.
• Display the sensor value and alarm state on the I2C LCD.
• Use non-blocking timing so other program activities can continue.

Example Environment Alarm Program

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

const int LDR_PIN = A0;
const int LED_PIN = 8;
const int BUZZER_PIN = 9;

const int THRESHOLD = 600;  // example only; calibrate during testing

LiquidCrystal_I2C lcd(0x27, 16, 2);

unsigned long lastRead = 0;
const unsigned long readInterval = 1000;

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  Serial.begin(9600);

  lcd.init();
  lcd.backlight();
}

void loop() {
  unsigned long now = millis();

  if (now – lastRead >= readInterval) {
    lastRead = now;
    int sensorValue = analogRead(LDR_PIN);

    Serial.print(“LDR: “);
    Serial.println(sensorValue);

    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print(“LDR: “);
    lcd.print(sensorValue);

    if (sensorValue > THRESHOLD) {
      digitalWrite(LED_PIN, HIGH);
      digitalWrite(BUZZER_PIN, HIGH);
      lcd.setCursor(0, 1);
      lcd.print(“ALARM”);
    } else {
      digitalWrite(LED_PIN, LOW);
      digitalWrite(BUZZER_PIN, LOW);
      lcd.setCursor(0, 1);
      lcd.print(“NORMAL”);
    }
  }
}

Teaching note: the threshold and I2C address are examples. Calibrate the threshold using the actual sensor and confirm the LCD address used in the laboratory.

9.4 Project Documentation Template

Item	Trainee entry
Project title
Problem being solved
Main requirements
Block diagram
Component list
Pin allocation
Program functions
Testing procedure
Fault encountered
Fault diagnosis
Solution implemented
Final result
Safety checks
Future improvement

9.5 Capstone Presentation Guide

1. State the project title and purpose.
2. Show and explain the block diagram.
3. Identify the important components and connections.
4. Demonstrate the working circuit.
5. Explain the timing, interrupt or RTOS element used.
6. Describe one problem encountered and how it was resolved.
7. Conclude by stating whether the requirements were achieved.

Assessment & Grading Rubric

The training module states that the capstone is graded summatively and that a trainee is competent upon achieving Competent or higher on all five criteria.

Criterion	Developing (1–2)	Competent (3–4)	Proficient (5)
Circuit Construction	Wiring incorrect or unsafe; major rework	Circuit functional with minor fixes	Correct, clean and safe on first test
Code Functionality	Does not compile/run as intended	Runs with minor logic errors	Runs correctly and handles edge cases
Understanding of Concepts	Cannot explain circuit/code	Explains most concepts with prompting	Clearly explains architecture, timing and logic
Debugging & Problem-Solving	Needs trainer to resolve most issues	Resolves issues with minor guidance	Independently diagnoses and fixes issues
Documentation & Safety	Lab sheet incomplete; unsafe practices	Lab sheet mostly complete; safe practices	Lab sheet complete, clear and all safety steps followed

Final Safety and Good Practice Checklist

• Power off before rewiring the breadboard.
• Check LED polarity and resistor placement.
• Keep the workstation orderly.
• Use the correct supply voltage for each board/module.
• Avoid short circuits between power and ground.
• Do not place long or blocking operations inside an ISR.
• Record faults, tests and corrections in the lab sheet.
• Test one section at a time before integrating the complete project.
• Ask the trainer for guidance when a wiring or hardware condition is uncertain.