Cucu Viorel-Cosmin 334CA

GitHub: PROIECT_PM_MASINUTA

MCU: ATmega328P Xplained Mini · PlatformIO

Land Buster is a small RC car (1/12 scale Land Buster chassis) that I upgraded into a smart rover. Instead of using a standard radio remote, I control it from my phone via Bluetooth.

The main idea was simple: a normal RC car does whatever you tell it, even if it is about to crash. I wanted to fix that. So I added sensors and automatic logic on top of the manual control.

What it does:

• You drive it with a phone app over Bluetooth. You can pick between 3 speed modes and honk the horn.
• The front ultrasonic sensor watches for obstacles. The buzzer starts beeping faster as you get closer. If you get too close (under 15 cm), the car stops by itself - you cannot override it.
• The headlights turn on automatically when it gets dark, based on a light sensor.
• The LCD screen shows the current speed mode and the distance to the nearest obstacle in real time.

Why it is useful: It shows how a cheap microcontroller can handle multiple real-time tasks at once - wireless communication, sensing, motor control, and display - using only hardware registers and no external libraries.

Course requirements met:

• 5 laboratory concepts: USART (Lab 1), Timers & Interrupts (Lab 2), PWM (Lab 3), ADC (Lab 4), I2C (Lab 6)
• 5 external peripherals: HC-05 Bluetooth, HC-SR04 Ultrasonic, 1602 I2C LCD, Photoresistor, Active Buzzer

The ATmega328P is the brain of the system. Everything connects to it.

• Inputs: Bluetooth commands from the phone, distance data from the ultrasonic sensor, light level from the photoresistor.
• Processing: The MCU reads all inputs, decides what to do (drive, stop, beep, light up), and sends signals to the outputs.
• Outputs: The ESC drives the main motor (speed), the L298N drives the steering motor (direction), the LCD shows status, the buzzer gives audio alerts, and the LEDs provide lighting.

kicad_cucu.pdf

The electrical schematic above illustrates the complete wiring of the Land Buster rover. The hardware architecture is built upon the following core engineering rules:

• Dual Isolated Power System: The system utilizes two separate battery packs. Battery 1 (Logic Rail) powers the L298N and the LM2596 regulator, which supplies a clean 5V to the MCU, sensors, and LCD. Battery 2 (Traction Rail) is dedicated exclusively to the high-current ESC. This isolation prevents massive voltage drops caused by the main motor from resetting the microcontroller.
• Common Ground: Despite having two isolated power sources, all ground (GND) connections across the entire system are tied together. This sets a unified 0V reference point, ensuring that PWM and digital logic signals are accurately interpreted by every component.
• LED Parallel Wiring: To ensure maximum brightness and protect the MCU pins, all 4 LEDs (2 front, 2 rear) are wired in parallel. Each LED connects to its respective MCU pin (D7 or A3) through its own dedicated 220Ω current-limiting resistor before returning to the common ground.
• HC-05 Level Shifting: The Bluetooth module operates at 3.3V logic. To prevent hardware damage, a simple voltage divider (1kΩ in series from MCU D1, then 2kΩ to GND) safely steps down the 5V USART TX signal to ≈3.3V before it reaches the module.
• Timer Selection Strategy: Timer 0 (8-bit) is used for the low-resolution steering PWM (Fast PWM, ~980 Hz). Timer 1 (16-bit) is strictly reserved for the ESC because it requires a precise 50 Hz period, which is impossible to achieve accurately with only 8 bits.

Photo 1: Power Drop Test\\

This early prototype test was conducted with only the steering system and ESC connected. While running the main traction motor at a low RPM, the output of the LM2596 regulator dropped dangerously to 4.7V. This critical observation proved that a single battery configuration was insufficient to handle the high current spikes, directly justifying the upgrade to the current dual-battery (4-cell) isolated power system.

Photo 2: Full System Test\\

All electronic components—including the ultrasonic sensors, I2C LCD, HC-05 Bluetooth module, and motor drivers—are integrated and tested together. This phase successfully verified the software integration, ensuring that the non-blocking logic, telemetry, and autonomous emergency braking (AEB) functioned simultaneously without interference, proving the system's core functionality.

Photo 3: Clean Build\\

The final hardware assembly mounted on the Land Buster chassis. This image highlights the strict cable management and the use of modular JST connectors. This robust wiring approach prevents connections from vibrating loose during physical operation, ensuring high reliability on the move.

Photo 4: Final Assembly\\

The completed autonomous rover with the original outer car shell successfully mounted. The clean cable management allows the shell to fit perfectly without putting pressure on the sensitive electronics or jumper wires, resulting in a polished and professional final build.

• IDE: PlatformIO (VS Code)
• Language: Pure AVR C
• Compiler: avr-gcc
• Target: ATmega328P Xplained Mini

src/
├── main.c          # Main loop, ISR, command dispatcher
├── usart.c / .h    # USART driver + printf via stdout (Lab 1)
├── ultrasonic.c    # HC-SR04 distance measurement (Lab 2)
├── motor.c         # PWM steering control via L298N (Lab 3)
├── adc.c / .h      # ADC driver for photoresistor (Lab 4)
└── task1.c         # ADC read + threshold logic (tested standalone)

The HC-05 sends bytes from the phone app at 9600 baud. The RX Complete Interrupt (RXCIE0) fires automatically when a byte arrives.

// usart.c
void USART0_init(unsigned int ubrr) {
    UBRR0H = (unsigned char)(ubrr >> 8);
    UBRR0L = (unsigned char)ubrr;
    UCSR0B = (1 << RXEN0) | (1 << TXEN0) | (1 << RXCIE0);
    UCSR0C = (1 << USBS0) | (3 << UCSZ00); // 8-bit, 2 stop bits
}

// main.c - ISR
volatile char comanda_bt = 0;
 
ISR(USART_RX_vect) {
    char c = UDR0;
    if (c != '\r' && c != '\n') comanda_bt = c;
}

Commands: F Forward, B Backward, L Left, R Right, S Stop, H Horn, 1/2/3 Speed mode.

Timer 1 measures the HC-SR04 echo pulse. At 16MHz prescaler 8, one tick = 0.5µs → distance_cm = ticks / 116.

// ultrasonic.c
uint16_t get_distance() {
    PORTD &= ~(1 << PD2); _delay_us(2);
    PORTD |=  (1 << PD2); _delay_us(10);
    PORTD &= ~(1 << PD2);
 
    uint32_t counter = 0;
    while (!(PIND & (1 << PD4))) {
        if (++counter > 100000) return 0;
    }
 
    TCNT1 = 0;
    TCCR1B = (1 << CS11);
    while (PIND & (1 << PD4)) {
        if (TCNT1 > 40000) break;
    }
    TCCR1B = 0;
    return TCNT1 / 116;
}

Timer 0 in Fast PWM mode on OC0A (PD6). OCR0A sets duty cycle (0-255). PB0/PB1 select direction.

// motor.c
void motor_steering_init() {
    DDRD |= (1 << PD6);
    DDRB |= (1 << PB0) | (1 << PB1);
    TCCR0A = (1 << COM0A1) | (1 << WGM01) | (1 << WGM00);
    TCCR0B = (1 << CS01) | (1 << CS00); // prescaler 64
    OCR0A = 0;
}
 
void motor_steer(int direction, uint8_t power) {
    OCR0A = power;
    if (direction == 1)       { PORTB |=  (1<<PB0); PORTB &= ~(1<<PB1); }
    else if (direction == -1) { PORTB &= ~(1<<PB0); PORTB |=  (1<<PB1); }
    else                      { PORTB &= ~(1<<PB0); PORTB &= ~(1<<PB1); }
}

Photoresistor on PC0 (ADC0) in voltage divider. When dark → LEDs turn on automatically.

// adc.c
void adc_init() {
    ADCSRA = (1 << ADEN) | (7 << ADPS0); // prescaler 128
    ADMUX  = (1 << REFS0);               // AVcc reference
}
 
uint16_t myAnalogRead(uint8_t channel) {
    ADMUX &= 0b11100000;
    ADMUX |= (channel & 0b00000111);
    ADCSRA |= (1 << ADSC);
    while (ADCSRA & (1 << ADSC));
    return ADC;
}

🔄 In progress. TWI hardware used at 100kHz. Registers: TWBR, TWSR, TWCR, TWDR. LCD will show speed mode and distance.

1. Collision prevention: Progressive buzzer + automatic emergency brake at 15cm.
2. Adaptive lighting: Headlights react to environment automatically.

Planned extra: Rear HC-SR04 for reverse parking assist.

This project shows that one small 8-bit microcontroller can handle wireless control, sensing, motor driving, and display - all at once -using only hardware registers.

Key lessons:

• Interrupts keep Bluetooth reception reliable without blocking the main loop.
• Hardware timers give accurate distance measurement.
• Separate power rails protect the MCU from motor noise and voltage drops.

All project files (C sources, Makefile / PlatformIO config, and schematics) are available in the GitHub repository: PROIECT_PM_MASINUTA GitHub

Task                              W1  W2  W3  W4  W5  W6  W7  W8  W9
──────────────────────────────────────────────────────────────────────
Planning & chassis setup          xxx xxx
Validate USART, ADC, Ultrasonic           xxx xxx
PWM speed & steering control                      xxx xxx
I2C LCD + emergency brake logic                           xxx xxx
Final assembly & testing                                          xxx

• ATmega328P Datasheet (Microchip Technology)
• HC-SR04 Ultrasonic Sensor
• LM2596 Step-Down Regulator (Texas Instruments)
• PCF8574 I2C Expander (Texas Instruments)
• HC-05 Bluetooth Module (Vendor documentation)
• GL5528 Photoresistor (Manufacturer datasheet)
• L298N H-Bridge (STMicroelectronics datasheet)

• PlatformIO + VS Code: Writing and uploading firmware
• avr-gcc + avr-size: Compiling and checking memory
• Serial Bluetooth Terminal (Android): Sending commands from phone

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