Embedded System (4343204) - Summer 2025 Solution

Question 1(a) [3 marks]

#

Discuss characteristics of real time operating system.

Answer:

Table: RTOS Characteristics

• Deterministic behavior: System responds within guaranteed time limits
• Multitasking support: Multiple tasks execute concurrently with priority
• Interrupt handling: Fast response to external events

Mnemonic: “RTOS Delivers Tasks Properly”

Question 1(b) [4 marks]

#

Describe AVR I/O port registers.

Answer:

Table: AVR I/O Port Registers

• DDRx register: Controls pin direction (0=input, 1=output)
• PORTx register: Sets output values or enables pull-up resistors
• PINx register: Reads current pin states for input operations

Mnemonic: “Direction, Port, Pin - DPP”

Question 1(c) [7 marks]

#

Compare different AVR microcontrollers and What are the factors to be considered in selecting the microcontroller for embedded system?

Answer:

Table: AVR Microcontroller Comparison

Selection Factors:

• Processing speed: Clock frequency requirements for application
• Memory requirements: Program and data storage needs
• I/O requirements: Number of pins needed for interfacing
• Power consumption: Battery life considerations for portable devices
• Cost factor: Budget constraints and volume requirements
• Development tools: Availability of compilers and debuggers

Mnemonic: “Speed, Memory, I/O, Power, Cost, Tools - SMIPCT”

Question 1(c OR) [7 marks]

#

Draw and explain general block diagram of embedded system.

Answer:

Diagram:

Components:

• Input section: Sensors and switches provide data to system
• Processing unit: Microcontroller executes program and controls operations
• Output section: Displays results and controls external devices
• Power supply: Provides regulated power to all components
• Memory: Stores program code and data permanently
• Communication: Interfaces with external systems via serial/wireless

Mnemonic: “Input, Process, Output, Power, Memory, Communication - IPOPMC”

Question 2(a) [3 marks]

#

Compare SRAM with EEPROM of ATMega32.

Answer:

Table: SRAM vs EEPROM Comparison

• Data retention: SRAM loses data on power-off, EEPROM retains data
• Usage purpose: SRAM for variables, EEPROM for configuration data

Mnemonic: “SRAM is Fast but Forgets, EEPROM Endures”

Question 2(b) [4 marks]

#

List Timer/counter 0 operation mode and explain anyone.

Answer:

Table: Timer0 Operation Modes

Normal Mode Explanation:

• Counter operation: Counts from 0x00 to 0xFF continuously
• Overflow flag: TOV0 flag set when counter overflows to 0x00
• Interrupt generation: Can generate interrupt on overflow condition

Mnemonic: “Normal Counts, PWM Pulses, CTC Clears”

Question 2(c) [7 marks]

#

With a sketch, identify and write function of each pins of ATmega32.

Answer:

Diagram: ATmega32 Pin Configuration

Pin Functions:

• Port A: 8-bit ADC input pins (PA0-PA7)
• Port B: SPI communication and timer functions
• Port C: JTAG interface and I2C communication
• Port D: UART communication and external interrupts
• Power pins: VCC, GND, AVCC for analog supply
• Crystal pins: XTAL1, XTAL2 for external oscillator

Mnemonic: “Analog-A, Bus-B, Communication-C, Data-D”

Question 2(a OR) [3 marks]

#

Explain data memory organization of ATmega32.

Answer:

Table: ATmega32 Memory Organization

• General purpose registers: R0-R31 for arithmetic operations
• I/O memory space: Control registers for peripherals
• Internal SRAM: Variable storage during program execution

Mnemonic: “Registers, I/O, SRAM - RIS”

Question 2(b OR) [4 marks]

#

Draw TIFR and TCCR registers of timer/counter 0.

Answer:

Diagram: Timer0 Registers

Bit Functions:

• TOV0: Timer0 overflow flag bit
• OCF0: Timer0 output compare match flag
• CS02:CS00: Clock select bits for prescaler
• WGM01:WGM00: Waveform generation mode bits

Mnemonic: “TIFR shows Flags, TCCR Controls Clock”

Question 2(c OR) [7 marks]

#

Draw and explain general block diagram of AVR microcontroller.

Answer:

Diagram: AVR Architecture

Components:

• CPU core: Executes instructions and controls system operation
• Program memory: Stores application code in non-volatile flash
• Data memory: Temporary storage for variables and stack
• ALU: Performs arithmetic and logical operations
• Register file: 32 general-purpose working registers
• I/O system: Interfaces with external hardware components
• Peripherals: Built-in modules like timers, UART, ADC

Mnemonic: “CPU Controls Program, Data, I/O, Peripherals - CPDIP”

Question 3(a) [3 marks]

#

Write an AVR C program to toggle all the bits of Port B continuously with a 10 ms delay.

Answer:

#include <avr/io.h>
#include <util/delay.h>

int main()
{
    DDRB = 0xFF;        // Set Port B as output
    
    while(1)
    {
        PORTB = 0xFF;    // Set all bits high
        _delay_ms(10);   // 10ms delay
        PORTB = 0x00;    // Set all bits low  
        _delay_ms(10);   // 10ms delay
    }
}

Key Points:

• DDRB = 0xFF: Configures all Port B pins as outputs
• PORTB toggle: Alternates between 0xFF and 0x00

Mnemonic: “DDR Direction, PORT Output”

Question 3(b) [4 marks]

#

Explain function of MAX232.

Answer:

Table: MAX232 Functions

• Voltage conversion: Converts 0-5V TTL to ±12V RS232 levels
• Serial communication: Enables microcontroller to communicate with PC
• Dual channel: Supports two-way communication simultaneously

Mnemonic: “MAX232 Makes Microcontroller Meet PC”

Question 3(c) [7 marks]

#

Write AVR C program to toggle all the bits of PORTC continuously with some delay. Use timer 0, mode 0 and no prescalar options to generate delay.

Answer:

#include <avr/io.h>

void timer0_delay()
{
    TCNT0 = 0;          // Initialize counter
    TCCR0 = 0x01;       // No prescaler, normal mode
    while(!(TIFR & (1<<TOV0))); // Wait for overflow
    TIFR |= (1<<TOV0);  // Clear overflow flag
    TCCR0 = 0;          // Stop timer
}

int main()
{
    DDRC = 0xFF;        // Port C as output
    
    while(1)
    {
        PORTC = 0xFF;    // All bits high
        for(int i=0; i<100; i++)
            timer0_delay(); // Multiple delays
            
        PORTC = 0x00;    // All bits low
        for(int i=0; i<100; i++)
            timer0_delay(); // Multiple delays
    }
}

Key Features:

• Timer0 normal mode: Counts from 0 to 255 then overflows
• No prescaler: Timer runs at system clock speed
• Overflow detection: TOV0 flag indicates timer overflow
• Delay generation: Multiple timer cycles create visible delay

Mnemonic: “Timer Counts, Overflow Flags, Generate Delays”

Question 3(a OR) [3 marks]

#

Write AVR C program to store #30h into location 0X011F of EEPROM.

Answer:

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

int main()
{
    eeprom_write_byte((uint8_t*)0x011F, 0x30);
    return 0;
}

Alternative Method:

#include <avr/io.h>

int main()
{
    while(EECR & (1<<EEWE));    // Wait for previous write
    EEAR = 0x011F;              // Set address
    EEDR = 0x30;                // Set data
    EECR |= (1<<EEMWE);         // Master write enable
    EECR |= (1<<EEWE);          // Write enable
}

Mnemonic: “Address, Data, Master, Write - ADMW”

Question 3(b OR) [4 marks]

#

Discuss different data types for programming AVR in C.

Answer:

Table: AVR C Data Types

• Memory efficiency: Choose smallest suitable data type
• Unsigned types: Use when negative values not needed
• Integer arithmetic: Faster than floating-point operations

Mnemonic: “Choose Correct Size for Memory Efficiency”

Question 3(c OR) [7 marks]

#

Write AVR C programs for serial data transmission.

Answer:

#include <avr/io.h>

void uart_init(unsigned int baud)
{
    UBRRH = (unsigned char)(baud>>8);
    UBRRL = (unsigned char)baud;
    UCSRB = (1<<TXEN);          // Enable transmitter
    UCSRC = (1<<URSEL)|(3<<UCSZ0); // 8-bit data
}

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

void uart_send_string(char *str)
{
    while(*str)
    {
        uart_transmit(*str++);
    }
}

int main()
{
    uart_init(51);              // 9600 baud at 8MHz
    
    while(1)
    {
        uart_send_string("Hello World\r\n");
        for(long i=0; i<100000; i++); // Delay
    }
}

Key Components:

• Baud rate setting: UBRR registers set communication speed
• Transmit enable: TXEN bit enables UART transmitter
• Data transmission: UDR register holds data to transmit
• Buffer check: UDRE flag indicates transmit buffer empty

Mnemonic: “Init, Enable, Check, Transmit - IECT”

Question 4(a) [3 marks]

#

Explain ADMUX register.

Answer:

Table: ADMUX Register Bits

• Reference voltage: Selects internal/external voltage reference
• Result format: ADLAR bit adjusts 10-bit result alignment
• Channel selection: MUX bits choose which ADC pin to read

Mnemonic: “Reference, Adjust, Channel - RAC”

Question 4(b) [4 marks]

#

Draw and explain Interfacing Relay with ATmega32.

Answer:

Diagram: Relay Interfacing

Components:

• Transistor switch: BC547 NPN transistor acts as electronic switch
• Base resistor: 1KΩ limits base current from microcontroller
• Relay coil: 12V relay operates external high-power devices
• Protection diode: Freewheeling diode protects from back EMF

Mnemonic: “Micro Controls Transistor Controls Relay”

Question 4(c) [7 marks]

#

Draw and explain TWI registers in AVR.

Answer:

Diagram: TWI Register Structure

Register Functions:

• TWCR: Controls TWI operation and interrupt handling
• TWSR: Provides status information and prescaler setting
• TWDR: Holds data for transmission/reception
• TWAR: Sets slave address when operating as slave
• TWBR: Sets bit rate for TWI communication
• TWINT: Interrupt flag cleared by writing 1
• Start/Stop: TWSTA and TWSTO control I2C conditions

Mnemonic: “Control, Status, Data, Address, Bit Rate - CSDAB”

Question 4(a OR) [3 marks]

#

Explain ADCSRA register.

Answer:

Table: ADCSRA Register Bits

• ADC control: ADEN enables ADC, ADSC starts conversion
• Interrupt system: ADIF flag set when conversion complete

Mnemonic: “Enable, Start, Trigger, Interrupt, Prescale - ESTIP”

Question 4(b OR) [4 marks]

#

Draw and explain interfacing of LM35 with ATmega32.

Answer:

Diagram: LM35 Interfacing

Connection Details:

• Power supply: LM35 requires +5V and ground connections
• Output voltage: Produces 10mV per degree Celsius
• ADC input: Connect LM35 output to ADC channel (PA0)
• Temperature calculation: °C = (ADC_Value × 5000mV) / (1024 × 10mV)

Code Example:

float temp = (adc_read() * 5.0 * 100.0) / 1024.0;

Mnemonic: “LM35 gives 10mV per degree”

Question 4(c OR) [7 marks]

#

Draw and explain interfacing of multiple 7-segment displays using MAX7221 with ATmega32.

Answer:

Diagram: MAX7221 Interfacing

Features:

• SPI communication: Uses serial peripheral interface for control
• Multiple displays: Controls up to 8 seven-segment displays
• Automatic scanning: MAX7221 handles multiplexing automatically
• Brightness control: Software-controlled brightness levels
• Decode mode: Built-in BCD to 7-segment decoder
• Low component count: Reduces external components needed

Key Registers:

• Decode mode register: Enables/disables BCD decoding
• Intensity register: Controls display brightness
• Scan limit register: Sets number of active displays
• Shutdown register: Normal operation or shutdown mode

Mnemonic: “SPI Sends Serial Data to Multiple Displays”

Question 5(a) [3 marks]

#

Explain SPCR register.

Answer:

Table: SPCR Register Bits

• SPI enable: SPE bit must be set to enable SPI functionality
• Master mode: MSTR bit determines if device is master or slave

Mnemonic: “Interrupt, Enable, Data, Master, Clock settings - IEDMC”

Question 5(b) [4 marks]

#

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

Answer:

Diagram: DC Motor Interfacing

Components:

• L293D driver: Provides current amplification for motor control
• Power supplies: +5V for logic, +12V for motor power
• Control signals: IN1, IN2 determine motor direction
• Enable pin: EN1 controls motor on/off and speed (PWM)

Mnemonic: “Logic controls Direction, Enable controls Speed”

Question 5(c) [7 marks]

#

Explain IoT based Home Automation System.

Answer:

Diagram: IoT Home Automation System

System Components:

• Internet connectivity: WiFi module connects system to internet
• Mobile application: User interface for remote control and monitoring
• Sensor network: Temperature, motion, light sensors for automation
• Control devices: Relays control home appliances and lights
• Central controller: Microcontroller processes commands and sensor data
• Cloud services: Store data and enable remote access

Features:

• Remote control: Control appliances from anywhere via internet
• Automation: Automatic control based on sensor readings
• Energy saving: Smart scheduling reduces power consumption
• Security monitoring: Motion sensors and cameras for safety
• Data logging: Historical data storage for analysis

Mnemonic: “Internet connects Phones to Home Devices - IPHD”

Question 5(a OR) [3 marks]

#

Explain SPSR register.

Answer:

Table: SPSR Register Bits

• Transfer complete: SPIF flag indicates SPI transmission finished
• Collision detection: WCOL flag shows write collision occurred
• Speed control: SPI2X doubles communication speed when set

Mnemonic: “Flag, Collision, Speed - FCS”

Question 5(b OR) [4 marks]

#

Draw and explain pin diagram of L293D motor driver IC.

Answer:

Diagram: L293D Pin Configuration

Pin Functions:

• Enable pins (EN1, EN2): Control motor on/off and speed via PWM
• Input pins (IN1-IN4): Logic inputs from microcontroller
• Output pins (OUT1-OUT4): High current outputs to motors
• Power supply (VCC1): +5V logic supply for IC operation
• Motor supply (VCC2): +12V supply for motor power
• Ground pins: Multiple ground connections for heat dissipation

Features:

• Dual H-bridge: Can control two DC motors simultaneously
• Current capacity: 600mA per channel, 1.2A peak
• Protection: Built-in flyback diodes for motor protection

Mnemonic: “Enable, Input, Output, Power - EIOP”

Question 5(c OR) [7 marks]

#

Explain Motorised Control Robotics System.

Answer:

Diagram: Robotics Control System

System Components:

Table: Robotics System Elements

Control Algorithm:

• Sense: Collect data from environment using sensors
• Process: Analyze sensor data and make decisions
• Act: Control motors and actuators based on decisions
• Feedback: Monitor actual movement and adjust control
• Communicate: Send status and receive commands remotely

Applications:

• Autonomous navigation: Robot moves independently using sensors
• Object manipulation: Gripper controlled for pick and place tasks
• Remote operation: Manual control via wireless communication
• Path following: Line following or predetermined route navigation
• Obstacle avoidance: Dynamic path planning around obstacles

Programming Structure:

while(1) {
    read_sensors();
    process_data();
    make_decision();
    control_motors();
    check_feedback();
    communicate_status();
}

Mnemonic: “Sense, Process, Act, Feedback, Communicate - SPACF”