Embedded System & Microcontroller Application (4351102) - Summer 2025 Solution

Question 1(a) [3 marks]

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State the features of ATmega32.

Answer:

• Operating Voltage: 2.7V to 5.5V range
• Clock Speed: Up to 16 MHz operation
• Communication: USART, SPI, I2C interfaces

Mnemonic: “Fast SRAM Enjoys Input Timers And Communication”

Question 1(b) [4 marks]

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Write criteria for choosing microcontroller.

Answer:

• Application Type: Real-time vs general purpose
• Communication Needs: Serial, parallel, wireless protocols
• Package Size: Space constraints in final product

Mnemonic: “Processing Memory I/O Power Cost Development Application Communication Package”

Question 1(c) [7 marks]

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Draw and explain general block diagram of embedded system.

Answer:

graph TD
    A[Input Devices] --> B[Processor/Microcontroller]
    B --> C[Output Devices]
    B <--> D[Memory]
    B <--> E[Communication Interface]
    F[Power Supply] --> B
    G[Clock/Timer] --> B

Block Functions:

• Processor: Central processing unit executing instructions
• Memory: Stores program code and data temporarily
• Input Devices: Sensors, switches providing system input
• Output Devices: Actuators, displays showing results
• Communication: Interfaces for external device connectivity
• Power Supply: Provides stable voltage to all components
• Clock/Timer: Synchronizes system operations and timing

Mnemonic: “Processors Memory Input Output Communication Power Clock”

Question 1(c OR) [7 marks]

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Define real time operating system and explain its characteristics.

Answer:

Real Time Operating System (RTOS): Operating system designed to process data and events within strict time constraints.

• Hard Real-time: Missing deadline causes system failure
• Soft Real-time: Missing deadline degrades performance
• Time Constraints: Operations must complete within deadlines

Mnemonic: “Deterministic Preemptive Multitasking Fast Priority Interrupt”

Question 2(a) [3 marks]

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Draw pin diagram of ATmega32.

Answer:

Mnemonic: “Port B A Reset Vcc Ground Crystal Port D C”

Question 2(b) [4 marks]

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Explain status register of ATmega32.

Answer:

• Status Register (SREG): Contains arithmetic operation results
• Flags Update: Automatically set/cleared by ALU operations
• Conditional Branching: Used for program flow control

Mnemonic: “I Think Half Sign Overflow Negative Zero Carry”

Question 2(c) [7 marks]

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Explain data memory of ATmega32 in detail.

Answer:

graph TD
    A[Data Memory Space] --> B[General Purpose Registers R0-R31]
    A --> C[I/O Memory 0x20-0x5F]
    A --> D[Extended I/O 0x60-0xFF]
    A --> E[Internal SRAM 0x100-0x8FF]

Memory Organization:

• General Purpose Registers: 32 registers (R0-R31) for data operations
• I/O Memory: Direct access to peripheral control registers
• Extended I/O: Additional peripheral registers and stack pointer
• Internal SRAM: 2KB volatile memory for variables and stack
• Address Space: Linear addressing from 0x00 to 0x8FF
• Stack Operation: Grows downward from high memory addresses

Mnemonic: “General I/O Extended SRAM Address Stack”

Question 2(a OR) [3 marks]

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Write functions of DDRx, PINx and PORTx registers.

Answer:

• DDRx Bit: 1 = Output, 0 = Input configuration
• PINx Read: Returns actual voltage level on pins
• PORTx Write: Controls output state when pin is output

Mnemonic: “Direction Input Output”

Question 2(b OR) [4 marks]

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Explain different I/O registers associated with EEPROM in AVR.

Answer:

EECR Control Bits:

• EERIE: EEPROM Ready Interrupt Enable
• EEMWE: EEPROM Master Write Enable
• EEWE: EEPROM Write Enable
• EERE: EEPROM Read Enable

Programming Sequence: Set address → Set data → Enable master write → Enable write

Mnemonic: “Address Data Control Ready Master Write Read”

Question 2(c OR) [7 marks]

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Explain different ways of connecting clock sources to the AVR.

Answer:

graph LR
    A[Crystal Oscillator] --> D[AVR Microcontroller]
    B[RC Oscillator] --> D
    C[Internal RC] --> D
    E[External Clock] --> D

Clock Configuration:

• Fuse Bits: CKSEL3:0 and SUT1:0 select clock source
• Startup Time: Different sources have varying startup delays
• Frequency Range: Internal RC provides 1MHz or 8MHz
• External Components: Crystal requires capacitors for stability

Mnemonic: “Crystal RC Internal External Fuse Startup Frequency Components”

Question 3(a) [3 marks]

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Write function of registers associated with Timer 1.

Answer:

• TIMSK: Timer Interrupt Mask register
• TIFR: Timer Interrupt Flag register

Mnemonic: “Timer Control Input Output Mask Flag”

Question 3(b) [4 marks]

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Discuss steps to program Timer0 in Normal mode.

Answer:

Programming Steps:

1. Set Timer Mode: Configure TCCR0 for Normal mode
2. Select Prescaler: Choose clock division ratio
3. Load Initial Value: Set TCNT0 register
4. Enable Interrupts: Set TOIE0 in TIMSK (if needed)
5. Start Timer: Set prescaler bits in TCCR0

TCCR0 = 0x05;    // Normal mode, prescaler 1024
TCNT0 = 0x00;    // Initial value
TIMSK |= 0x01;   // Enable overflow interrupt

Mnemonic: “Set Select Load Enable Start”

Question 3(c) [7 marks]

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Write a C program to receive bytes of data serially and put them on PORT A. Set the baud rate at 9600, 8-bit, and 1 stop bit.

Answer:

#include <avr/io.h>

void USART_Init() {
    // Set baud rate to 9600 (assuming 8MHz clock)
    UBRRH = 0x00;
    UBRRL = 51;
    
    // Enable receiver
    UCSRB = (1<<RXEN);
    
    // Set frame format: 8 data bits, 1 stop bit
    UCSRC = (1<<URSEL)|(3<<UCSZ0);
}

unsigned char USART_Receive() {
    // Wait for data to be received
    while(!(UCSRA & (1<<RXC)));
    return UDR;
}

int main() {
    DDRA = 0xFF;        // PORTA as output
    USART_Init();       // Initialize USART
    
    while(1) {
        PORTA = USART_Receive();  // Receive and display
    }
    return 0;
}

Mnemonic: “Initialize Receive Display Loop”

Question 3(a OR) [3 marks]

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Write function of registers associated with Serial Communication in AVR.

Answer:

Key Functions: Data transmission/reception, status monitoring, control configuration

Mnemonic: “Data Control Status Baud”

Question 3(b OR) [4 marks]

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Discuss steps to program AVR to transfer data serially.

Answer:

Programming Steps:

1. Set Baud Rate: Configure UBRRH/UBRRL registers
2. Enable Transmitter: Set TXEN bit in UCSRB
3. Set Frame Format: Configure data bits, stop bits in UCSRC
4. Wait for Empty Buffer: Check UDRE flag in UCSRA
5. Load Data: Write data to UDR register

void USART_Transmit(unsigned char data) {
    while(!(UCSRA & (1<<UDRE)));  // Wait for empty buffer
    UDR = data;                   // Send data
}

Mnemonic: “Baud Enable Format Wait Load”

Question 3(c OR) [7 marks]

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Write a C program to toggle only the PORTB.4 bit continuously every 2 ms. Use timer 1, Normal mode, and no prescaler to create the delay. Assume XTAL=8MHz.

Answer:

#include <avr/io.h>
#include <avr/interrupt.h>

volatile unsigned int timer_count = 0;

ISR(TIMER1_OVF_vect) {
    timer_count++;
    if(timer_count >= 1) {  // Approximately 2ms
        PORTB ^= (1<<4);    // Toggle PORTB.4
        timer_count = 0;
        TCNT1 = 49911;      // Reload for 2ms delay
    }
}

int main() {
    DDRB |= (1<<4);         // PORTB.4 as output
    
    // Timer1 Normal mode, no prescaler
    TCCR1A = 0x00;
    TCCR1B = 0x01;          // No prescaler
    
    TCNT1 = 49911;          // Initial value for 2ms
    TIMSK |= (1<<TOIE1);    // Enable Timer1 overflow interrupt
    
    sei();                  // Enable global interrupts
    
    while(1) {
        // Main loop
    }
    return 0;
}

Calculation: For 2ms delay with 8MHz clock: 8MHz × 2ms = 16000 cycles Timer1 counts: 65536 - 16000 = 49536 (approximately 49911 for adjustment)

Mnemonic: “Configure Timer Calculate Enable Loop”

Question 4(a) [3 marks]

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Draw interfacing diagram of ULN2803 with ATmega32.

Answer:

Connection Details:

• Input: ATmega32 PORTB pins to ULN2803 inputs
• Output: ULN2803 outputs drive high current loads
• Common: Pin 9 connects to positive supply, Pin 10 to ground

Mnemonic: “Input Output Common Supply Ground”

Question 4(b) [4 marks]

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Write an AVR C program to get a byte of data from Port B, and then send it to Port C.

Answer:

#include <avr/io.h>

int main() {
    DDRB = 0x00;    // PORTB as input
    DDRC = 0xFF;    // PORTC as output
    PORTB = 0xFF;   // Enable pull-up resistors on PORTB
    
    unsigned char data;
    
    while(1) {
        data = PINB;     // Read data from PORTB
        PORTC = data;    // Send data to PORTC
    }
    
    return 0;
}

Program Flow:

• Configure Ports: Set direction registers
• Enable Pull-ups: Activate internal pull-up resistors
• Read Data: Get byte from PINB register
• Write Data: Output byte to PORTC register

Mnemonic: “Configure Enable Read Write”

Question 4(c) [7 marks]

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Draw and explain interfacing of MAX7221 with ATmega32.

Answer:

Interface Description:

• SPI Communication: Uses 3-wire SPI protocol
• DIN (Data In): Serial data input from PB5 (MOSI)
• CLK (Clock): Clock signal from PB7 (SCK)
• LOAD (Chip Select): Latch signal from PB4 (SS)
• Multiplexed Display: Controls up to 8 seven-segment digits
• Current Control: Internal current limiting for LEDs

Programming Steps: Initialize SPI → Send address → Send data → Toggle LOAD pin

Mnemonic: “SPI Data Clock Load Multiplex Current Program”

Question 4(a OR) [3 marks]

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Draw interfacing diagram of LM35 with ATmega32.

Answer:

Connection Details:

• VCC: Connect to +5V supply
• OUT: Analog output to ADC channel (PA0)
• GND: Connect to ground
• Output: 10mV/°C linear voltage output

Mnemonic: “VCC OUT GND Linear”

Question 4(b OR) [4 marks]

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Write an AVR C program to monitor bit 5 of port C, if it is HIGH, send 55H to Port B; otherwise, send AAH to Port B.

Answer:

#include <avr/io.h>

int main() {
    DDRC &= ~(1<<5);    // PC5 as input
    DDRB = 0xFF;        // PORTB as output
    PORTC |= (1<<5);    // Enable pull-up on PC5
    
    while(1) {
        if(PINC & (1<<5)) {     // Check if bit 5 is HIGH
            PORTB = 0x55;       // Send 55H to PORTB
        }
        else {
            PORTB = 0xAA;       // Send AAH to PORTB
        }
    }
    
    return 0;
}

Program Logic:

• Monitor Bit: Check PC5 status using bit masking
• Conditional Output: Send different values based on input
• Continuous Loop: Monitor continuously for changes

Mnemonic: “Monitor Conditional Output Loop”

Question 4(c OR) [7 marks]

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Discuss registers used to program SPI in the AVR.

Answer:

SPCR Control Bits:

• SPIE: SPI Interrupt Enable
• SPE: SPI Enable
• DORD: Data Order (MSB/LSB first)
• MSTR: Master/Slave Select
• CPOL: Clock Polarity
• CPHA: Clock Phase
• SPR1:0: SPI Clock Rate Select

SPSR Status Bits:

• SPIF: SPI Interrupt Flag
• WCOL: Write Collision Flag
• SPI2X: Double SPI Speed

Programming Sequence: Configure SPCR → Enable SPI → Write SPDR → Wait for SPIF → Read SPDR

Mnemonic: “Control Status Data Configure Enable Write Wait Read”

Question 5(a) [3 marks]

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Draw pin diagram of L293D motor driver IC.

Answer:

Pin Functions:

• EN1, EN2: Enable pins for motor control
• 1A, 2A, 3A, 4A: Input pins from microcontroller
• 1Y, 2Y, 3Y, 4Y: Output pins to motors
• VCC: Logic and motor supply voltages
• GND: Ground connections

Mnemonic: “Enable Input Output Supply Ground”

Question 5(b) [4 marks]

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Draw and explain ADMUX register.

Answer:

Bit Functions:

• REFS1:0: Reference Selection (00=AREF, 01=AVCC, 11=Internal 2.56V)
• ADLAR: ADC Left Adjust Result (data format)
• MUX4:0: Analog Channel Selection (32 possible channels)

Channel Selection Examples:

• 00000: ADC0 (PA0)
• 00001: ADC1 (PA1)
• 00111: ADC7 (PA7)

Mnemonic: “Reference Adjust Multiplex Channel”

Question 5(c) [7 marks]

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Explain the block diagram of GSM based security system.

Answer:

graph TD
    A[Sensors] --> B[Microcontroller]
    B --> C[GSM Module]
    C --> D[Mobile Network]
    D --> E[User Mobile]
    B --> F[Alarm System]
    B --> G[Display Unit]
    H[Power Supply] --> B
    H --> C

System Components:

• Sensors: PIR, door/window sensors detect intrusion
• Microcontroller: Processes sensor data and controls system
• GSM Module: Sends SMS/calls to registered numbers
• Mobile Network: Connects to cellular infrastructure
• Alarm System: Local audio/visual alerts
• Display Unit: Shows system status and messages
• Power Supply: Battery backup for continuous operation

Operation Flow: Sensor detects → Microcontroller processes → GSM sends alert → User receives notification → Alarm activates

Mnemonic: “Sensors Microcontroller GSM Mobile Alarm Display Power Operation”

Question 5(a OR) [3 marks]

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Draw circuit diagram to interface DC motor with ATmega32 using L293D motor driver.

Answer:

Connections:

• PB0 → EN1: Enable motor operation
• PB1 → 1A, PB2 → 2A: Direction control inputs
• 1Y, 2Y → Motor: Output to motor terminals
• VCC, GND: Power supply connections

Motor Control: Different input combinations on 1A, 2A control motor direction and speed

Mnemonic: “Enable Direction Output Power Control”

Question 5(b OR) [4 marks]

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Draw and explain ADCSRA register.

Answer:

Bit Functions:

• ADEN: ADC Enable
• ADSC: ADC Start Conversion
• ADATE: ADC Auto Trigger Enable
• ADIF: ADC Interrupt Flag
• ADIE: ADC Interrupt Enable
• ADPS2:0: ADC Prescaler Select (division factor)

Prescaler Settings: 000=2, 001=2, 010=4, 011=8, 100=16, 101=32, 110=64, 111=128

Programming: Set ADEN → Configure prescaler → Set ADSC → Wait for ADIF

Mnemonic: “Enable Start Auto Interrupt Prescaler Configure”

Question 5(c OR) [7 marks]

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Explain the block diagram of Weather monitoring system.

Answer:

graph TD
    A[Temperature Sensor] --> E[Microcontroller]
    B[Humidity Sensor] --> E
    C[Pressure Sensor] --> E
    D[Rain Sensor] --> E
    E --> F[LCD Display]
    E --> G[Data Logger]
    E --> H[Wireless Module]
    H --> I[Remote Monitoring]
    J[Power Supply] --> E
    E --> K[Alarm System]

System Components:

• Temperature Sensor: Measures ambient temperature (LM35/DS18B20)
• Humidity Sensor: Monitors moisture content (DHT22)
• Pressure Sensor: Detects atmospheric pressure changes
• Rain Sensor: Detects precipitation levels
• Microcontroller: Central processing unit for data collection
• LCD Display: Local visual data presentation
• Data Logger: Stores historical weather data
• Wireless Module: Transmits data to remote locations
• Alarm System: Alerts for extreme weather conditions

Operation: Sensors collect data → Microcontroller processes → Display updates → Data logging → Wireless transmission → Alert generation

Mnemonic: “Temperature Humidity Pressure Rain Microcontroller Display Logger Wireless Alarm Operation”