Memory	Function
Flash	Stores program
SRAM	Stores temporary variables
EEPROM	Stores data that must remain after power is removed

IMAGE

You can build the circuit on a breadboard without an Arduino board.

USBasp is an ISP programmer.

ISP = In-System Programming.

It allows you to program the ATmega328P directly.

USBasp	ATmega328P
MOSI	PB3 / Pin 17
MISO	PB4 / Pin 18
SCK	PB5 / Pin 19td>
RESET	PC6 / Pin 1
VCC	Pin 7
GND	Pin 8/22

The programming path is:

Computer → USB → USBasp → ISP → ATmega328P

You need two important tools.

AVR-GCC

Used to compile C source code.

main.c → avr-gcc → main.elf

AVR-Objcopy

Converts the ELF file into HEX.

main.elf → avr-objcopy → main.hex

AVRDude

Transfers the HEX file to the ATmega.

main.hex → avrdude → USBasp → ATmega328P

#include
#include

#define F_CPU 16000000UL

int main(void)
{
DDRB |= (1 << PB5);

while (1)
{
PORTB |= (1 << PB5);

_delay_ms(1000);

PORTB &= ~(1 << PB5);

_delay_ms(1000);
}

return 0;
}

This makes PB5 HIGH and LOW repeatedly.

Program:

#include
#include

#define F_CPU 16000000UL

int main(void)
{
DDRB |= (1 << PB5);

while (1)
{
PORTB |= (1 << PB5);
_delay_ms(500);

PORTB &= ~(1 << PB5);
_delay_ms(500);
}
}

Connect a button to PD2.

A convenient method is using the internal pull-up resistor.

#include
#include

#define F_CPU 16000000UL

int main(void)
{
DDRB |= (1 << PB5);

DDRD &= ~(1 << PD2);

PORTD |= (1 << PD2);

while (1)
{
if (!(PIND & (1 << PD2)))
{
PORTB |= (1 << PB5);
}
else
{
PORTB &= ~(1 << PB5);
}
}
}

program :

#define F_CPU 16000000UL

#include
#include

const unsigned char digit[10] =
{
0x3F, // 0
0x06, // 1
0x5B, // 2
0x4F, // 3
0x66, // 4
0x6D, // 5
0x7D, // 6
0x07, // 7
0x7F, // 8
0x6F // 9
};

void display_digit(unsigned char number)
{
if (number <= 9)
{
PORTD = digit[number];
}
}

int main(void)
{
// PD0-PD6 as outputs
DDRD = 0x7F;

while (1)
{
display_digit(0);
_delay_ms(1000);

display_digit(1);
_delay_ms(1000);

display_digit(2);
_delay_ms(1000);

display_digit(3);
_delay_ms(1000);

display_digit(4);
_delay_ms(1000);

display_digit(5);
_delay_ms(1000);

display_digit(6);
_delay_ms(1000);

display_digit(7);
_delay_ms(1000);

display_digit(8);
_delay_ms(1000);

display_digit(9);
_delay_ms(1000);
}
}

USING ARDUINO UNO

// Arduino Uno + Common Cathode 7-Segment Display

// Segment pins
int a = 2;
int b = 3;
int c = 4;
int d = 5;
int e = 6;
int f = 7;
int g = 8;

void setup()
{
pinMode(a, OUTPUT);
pinMode(b, OUTPUT);
pinMode(c, OUTPUT);
pinMode(d, OUTPUT);
pinMode(e, OUTPUT);
pinMode(f, OUTPUT);
pinMode(g, OUTPUT);
}

void displayDigit(int number)
{
// Turn all segments OFF first
digitalWrite(a, LOW);
digitalWrite(b, LOW);
digitalWrite(c, LOW);
digitalWrite(d, LOW);
digitalWrite(e, LOW);
digitalWrite(f, LOW);
digitalWrite(g, LOW);

if (number == 0)
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(e, HIGH);
digitalWrite(f, HIGH);
}

else if (number == 1)
{
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
}

else if (number == 2)
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(g, HIGH);
digitalWrite(e, HIGH);
digitalWrite(d, HIGH);
}

else if (number == 3)
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(g, HIGH);
}

else if (number == 4)
{
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
}

else if (number == 5)
{
digitalWrite(a, HIGH);
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
}

else if (number == 6)
{
digitalWrite(a, HIGH);
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
digitalWrite(e, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
}

else if (number == 7)
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
}

else if (number == 8)
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(e, HIGH);
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
}

else if (number == 9)
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
}
}

void loop()
{
// Count from 0 to 9
for (int number = 0; number <= 9; number++)
{
displayDigit(number);
delay(1000);
}
}