Raspberry Pi 5

LED Blink & HC-SR04 Ultrasonic Distance Sensor

Embedded C | GPIO Programming | WiringPi | Linux

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📌 Project Overview

This project demonstrates low-level GPIO control and real-time sensor interfacing on Raspberry Pi 5 using Embedded C and the WiringPi library.

The project follows a professional embedded systems workflow and is suitable for:

• Embedded Systems practice
• Firmware fundamentals
• Raspberry Pi GPIO learning
• Academic labs and technical interviews

All programs are written in C, compiled using gcc, and tested on real Raspberry Pi 5 hardware.

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🎯 Features

• GPIO output control (LED blinking)
• GPIO input pulse measurement (HC-SR04)
• Ultrasonic distance calculation using Time-of-Flight
• BCM GPIO numbering
• nano-based development workflow
• Clean compilation and execution on Linux

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🧰 Hardware Requirements

Component	Specification
Raspberry Pi	Raspberry Pi 5
LED	5 mm
Resistor	220 Ω
Ultrasonic Sensor	HC-SR04
Breadboard	Standard
Jumper Wires	Male–Male
Power Supply	5 V (Official Recommended)

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🔌 GPIO Pin Configuration (BCM Numbering)

LED Wiring

Signal	GPIO	Physical Pin
LED Anode (+)	GPIO 17	Pin 11
LED Cathode (−)	GND	Pin 6

Connection:

GPIO17 → 220Ω → LED(+)
LED(−) → GND

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HC-SR04 Ultrasonic Sensor Wiring

Sensor Pin	GPIO	Physical Pin
VCC	5 V	Pin 2 / 4
GND	GND	Pin 6
TRIG	GPIO 17	Pin 11
ECHO	GPIO 27	Pin 13

⚠️ Important Note:
HC-SR04 ECHO outputs 5 V, while Raspberry Pi GPIO operates at 3.3 V.
For production-safe designs, use a voltage divider on the ECHO pin.

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💻 Software Requirements

• Raspberry Pi OS (64-bit recommended)
• GCC Compiler
• WiringPi Library
• nano Text Editor

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🔧 System Setup

Update system:

sudo apt update
sudo apt upgrade -y

Install build tools:

sudo apt install -y build-essential git

Verify GCC:

gcc --version

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📦 WiringPi Installation

git clone https://github.com/WiringPi/WiringPi.git
cd WiringPi
./build

Verify installation:

gpio -v

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📁 Project Directory Structure

Raspberry-Pi-LED-Ultrasonic-Project/
│
├── README.md
├── src/
│   ├── led_blink.c
│   └── ultrasonic_sensor.c
│
├── docs/
└── photos/

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✍️ Using nano Editor

Create a file:

nano src/led_blink.c

Save and exit:

• Save → CTRL + O → Enter
• Exit → CTRL + X

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🧪 Program 1: LED Blink

File: src/led_blink.c

#include <wiringPi.h>
#include <stdio.h>
#include <unistd.h>

#define LED_PIN 17

int main(void)
{
    if (wiringPiSetupGpio() == -1)
    {
        printf("Error: WiringPi initialization failed\n");
        return 1;
    }

    pinMode(LED_PIN, OUTPUT);

    for (int i = 0; i < 10; i++)
    {
        digitalWrite(LED_PIN, HIGH);
        printf("LED ON\n");
        sleep(1);

        digitalWrite(LED_PIN, LOW);
        printf("LED OFF\n");
        sleep(1);
    }

    return 0;
}

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📏 Program 2: Ultrasonic Distance Measurement

File: src/ultrasonic_sensor.c

#include <wiringPi.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>

#define TRIG_PIN 17
#define ECHO_PIN 27

float measureDistance(void)
{
    digitalWrite(TRIG_PIN, HIGH);
    delayMicroseconds(10);
    digitalWrite(TRIG_PIN, LOW);

    while (digitalRead(ECHO_PIN) == LOW);

    struct timespec start, end;
    clock_gettime(CLOCK_MONOTONIC, &start);

    while (digitalRead(ECHO_PIN) == HIGH);

    clock_gettime(CLOCK_MONOTONIC, &end);

    long duration = (end.tv_nsec - start.tv_nsec) / 1000;
    return (duration * 0.0343f) / 2.0f;
}

int main(void)
{
    if (wiringPiSetupGpio() == -1)
    {
        printf("Error: WiringPi initialization failed\n");
        return 1;
    }

    pinMode(TRIG_PIN, OUTPUT);
    pinMode(ECHO_PIN, INPUT);

    while (1)
    {
        float distance = measureDistance();
        printf("Distance: %.2f cm\n", distance);
        sleep(1);
    }

    return 0;
}

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⚙️ Compilation

cd ~/Raspberry-Pi-LED-Ultrasonic-Project

gcc src/led_blink.c -o led_blink -lwiringPi
gcc src/ultrasonic_sensor.c -o ultrasonic_sensor -lwiringPi

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▶️ Execution

⚠️ GPIO access requires sudo

sudo ./led_blink
sudo ./ultrasonic_sensor

Stop program:

CTRL + C

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🛠 Troubleshooting

WiringPi not found

sudo apt install wiringpi

Permission denied

chmod +x led_blink ultrasonic_sensor

LED not glowing

• Check LED polarity
• Verify 220 Ω resistor
• Confirm GPIO 17 connection

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📚 Learning Outcomes

• GPIO configuration using WiringPi
• Embedded C programming on Linux
• Ultrasonic sensor timing & distance calculation
• Hardware–software integration
• Professional embedded workflow

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👤 Author

Ram Axay
Embedded Systems & Firmware Engineer

GitHub: https://github.com/AxayRam

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📄 License

MIT License — Free to use, modify, and distribute.

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