Smart Home Control System Using Ultrasonic Sensor

Teammate MithunKumar Selvakumar Sumithra - (Id-16489646) ManojKumar Reddy Nimmala - (Id-16276943)

Smart Fan Control System

Ultrasonic Sensor | STM32 Nucleo-F446RE | L298N Motor Driver | Raspberry Pi

Project Overview

This project is a Smart Home Control System that automatically turns a led on or off based on the distance of a person. It uses an ultrasonic sensor to measure distance, an STM32 Nucleo-F446RE microcontroller to handle control logic, an L298N motor driver to power the fan, and a Raspberry Pi for monitoring and an optional user interface.

The primary goal is to design a simple, responsive, and energy-efficient fan system that responds to human presence, such as when someone approaches or leaves the room.

Key Features • Detects presence using an HC-SR04 ultrasonic sensor. • Controls fan speed with PWM signals from the STM32. • Drives a DC fan motor through the L298N motor driver. • Sends real-time data to Raspberry Pi through UART. • Optional dashboard or data logging on Raspberry Pi. • Adjustable distance threshold and fan speed control.

Components Used

Component Quantity Description •STM32 Nucleo-F446RE 1 Main microcontroller board •Raspberry Pi (3/4) 1 Used for monitoring/logging •Ultrasonic Sensor (HC-SR04) 1 Detects distance/presence •L298N Motor Driver 1 Controls DC motor (fan) •DC Fan (12V) 1 Load device •12V Power Supply 1 for motor driver •led 1 for display led on/off •Jumper Wires & Breadboard – For circuit connections

Circuit Connections

Ultrasonic Sensor (HC-SR04 → STM32)

HC-SR04 Pin STM32 Pin Description VCC 5V Power GND GND Ground TRIG PA9 Trigger Pin ECHO PA8 Echo Pin (with voltage divider)

Note: The ECHO pin outputs 5V. Use a resistor divider or level shifter to protect the STM32’s 3.3V input.

L298N Motor Driver (→ STM32)

L298N Pin STM32 Pin Function •ENA PB6 PWM output (TIM4 Channel 1) •IN1 PB4 Direction Control •IN2 PB5 Direction Control •+12V 12V Supply Motor power •GND Common Ground Shared with STM32 & Pi

UART Communication (STM32 ↔ Raspberry Pi)

•STM32 Pin	Raspberry Pi Pin	Function
•PA2 (TX)	GPIO15 (RX)	Serial transmit
•PA3 (RX)	GPIO14 (TX)	Serial receive
•GND	GND	Common ground

Enable UART on Raspberry Pi and disable console serial login for clean communication.

System Workflow 1. The ultrasonic sensor continuously measures distance. 2. If an object (person) is within a preset range (e.g., < 120 cm), the STM32 activates the fan. 3. Fan speed increases as the object gets closer (optional scaling). 4. When the object moves away, the fan slows down or turns off. 5. The STM32 sends distance and fan status data to the Raspberry Pi via UART. 6. The Raspberry Pi can log the data or display it on a simple web dashboard.

Software & Tools • STM32CubeIDE or PlatformIO (VS Code) – for STM32 firmware. • Python (Raspberry Pi) – for reading serial data and optional UI. • Blynk / Flask (optional) – for IoT dashboard or local monitoring.

STM32 Firmware (Logic Summary) 1. Initialize peripherals: GPIO, Timer (PWM), UART, and ultrasonic pins. 2. Trigger ultrasonic pulse: 10 µs HIGH on TRIG pin. 3. Measure ECHO pulse width: Convert it to distance in centimeters. 4. Compare distance: • If within threshold → turn led ON (set PWM). • If out of range → turn the led OFF. 5. Send distance and fan status over UART to Raspberry Pi.

[env:nucleo_f446re] platform = ststm32 board = nucleo_f446re framework = mbed upload_protocol = stlink monitor_speed = 115200

It’s a small step toward creating smarter and more energy-efficient living environments. #include "mbed.h" #include #include using namespace std::chrono;

// Serial debug UnbufferedSerial pc(USBTX, USBRX, 115200);

// Ultrasonic sensor pins DigitalOut trig(PA_8); DigitalIn echo(PB_10);

// Motor driver pins DigitalOut motorIN1(PB_4); DigitalOut motorIN2(PB_5); PwmOut motorENA(PB_6); // motor enable pin (PWM optional)

// External LED pin DigitalOut led(PB_0); // External LED connected here

Timer t;

void triggerPulse() { trig = 0; wait_us(2); trig = 1; wait_us(10); trig = 0; }

float getDistance() { triggerPulse(); t.reset(); t.start();

while (!echo.read());
auto start = t.elapsed_time().count();

while (echo.read());
auto stop = t.elapsed_time().count();

t.stop();
float distance_cm = (stop - start) / 58.0f;
return distance_cm;

}

void motorForward(float speed) { motorIN1 = 1; motorIN2 = 0; motorENA.write(speed); }

void motorStop() { motorIN1 = 0; motorIN2 = 0; motorENA.write(0.0f); }

int main() { pc.write("Ultrasonic + DC motor + External LED start\r\n", 47); motorENA.period_ms(20); // 50Hz PWM for motor

const float threshold_cm = 50.0f;  // detection range

while (true) {
    float distance = getDistance();

    char buf[64];
    int n = sprintf(buf, "Distance: %.2f cm\r\n", distance);
    pc.write(buf, n);

    if (distance > 0 && distance <= threshold_cm) {
        pc.write("Motion detected -> Motor & LED ON\r\n", 38);
        motorForward(0.9f);
        led = 1; // LED ON
    } else {
        pc.write("No motion -> Motor & LED OFF\r\n", 33);
        motorStop();
        led = 0; // LED OFF
    }

    ThisThread::sleep_for(500ms);
}

}

Raspberry Pi Side

import serial import time { ser = serial.Serial('/dev/ttyS0', 115200, timeout=1)

while True: data = ser.readline().decode().strip() if data: print("Data from STM32:", data) time.sleep(0.2) }

For Raspberry Pi we have added more

sudo apt update sudo apt install gawk wget git diffstat unzip texinfo gcc build-essential chrpath socat cpio python3 python3-pip python3-pexpect xz-utils debianutils iputils-ping python3-git python3-jinja2 libegl1-mesa libsdl1.2-dev pylint3 xterm

yocto source mkdir ~/yocto-dcmotor cd ~/yocto-dcmotor git clone -b scarthgap git://git.yoctoproject.org/poky.git cd poky git clone -b scarthgap https://github.com/agherzan/meta-raspberrypi.git

custom layer cd ~/yocto-dcmotor/poky source oe-init-build-env bitbake-layers create-layer ../meta-dcmotor bitbake-layers add-layer ../meta-dcmotor bitbake-layers add-layer ../meta-raspberrypi

folder structure yocto-dcmotor/ ├── poky/ │ ├── meta/ │ ├── meta-poky/ │ ├── meta-yocto-bsp/ │ └── meta-raspberrypi/ └── meta-dcmotor/ ├── conf/ │ └── layer.conf └── recipes-example/ └── dcmotor/ ├── dcmotor.bb └── files/ └── motor_control.p

To Add the Recipe DESCRIPTION = "Raspberry Pi DC Motor ON/OFF with LED" LICENSE = "MIT" SRC_URI = "file://motor_control.py" S = "${WORKDIR}"

RDEPENDS:${PN} += "python3 python3-rpi-gpio"

do_install() { install -d ${D}${bindir} install -m 0755 ${WORKDIR}/motor_control.py ${D}${bindir}/motor_control.py }

Python Code #!/usr/bin/env python3 import RPi.GPIO as GPIO import time

IN1 = 17 IN2 = 27 ENA = 22 LED = 23

GPIO.setmode(GPIO.BCM) GPIO.setup(IN1, GPIO.OUT) GPIO.setup(IN2, GPIO.OUT) GPIO.setup(ENA, GPIO.OUT) GPIO.setup(LED, GPIO.OUT)

pwm = GPIO.PWM(ENA, 1000) pwm.start(0)

try: while True: print("Motor ON") GPIO.output(IN1, GPIO.HIGH) GPIO.output(IN2, GPIO.LOW) GPIO.output(LED, GPIO.HIGH) pwm.ChangeDutyCycle(80) time.sleep(3)

    print("Motor OFF")
    GPIO.output(IN1, GPIO.LOW)
    GPIO.output(IN2, GPIO.LOW)
    GPIO.output(LED, GPIO.LOW)
    pwm.ChangeDutyCycle(0)
    time.sleep(3)

except KeyboardInterrupt: pwm.stop() GPIO.cleanup()

To modify the local conf MACHINE = "raspberrypi3" DISTRO ?= "poky" PACKAGE_CLASSES ?= "package_rpm" EXTRA_IMAGE_FEATURES ?= "debug-tweaks ssh-server-dropbear" USER_CLASSES ?= "buildstats image-mklibs image-prelink" PATCHRESOLVE = "noop" BB_DISKMON_DIRS = "STOPTASKS,${TMPDIR},1G,STOP;STOPTASKS,${DL_DIR},1G,STOP;STOPTASKS,${SSTATE_DIR},1G,STOP" IMAGE_INSTALL:append = " python3 python3-rpi-gpio dcmotor" GPU_MEM = "16" ENABLE_UART = "1"

BBLAYERS ?= "
${TOPDIR}/../meta
${TOPDIR}/../meta-poky
${TOPDIR}/../meta-yocto-bsp
${TOPDIR}/../meta-raspberrypi
${TOPDIR}/../meta-dcmotor
"

Applications • Smart home automation. • Energy-efficient ventilation. • Contactless control in labs or hospitals. • IoT-based smart appliances.

Future Improvements • Add temperature & humidity sensors (e.g., SHT31). • Integrate Wi-Fi or Bluetooth control. • Add Display(LCD or OLED) for live readings. • Implement mobile app control using Blynk or MQTT. Author

Project by: Mithunkumar Selvakumar Sumithra & Manojkumar Nimmala Field: Embedded Programming Applications Microcontroller Used: STM32 Nucleo-F446RE Language: C (STM32 HAL) + Python (Raspberry Pi)

Conclusion

This project demonstrates how a basic DC fan can be transformed into a smart, automated system using readily available components. It combines sensor-based automation, motor control, and IoT connectivity — all built on top of open-source hardware.

selvakum7/Mithun-16489646-Manoj-kumar-16276943

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