Question

write the code of 4 digit 7-segment display using arduino uno in assembly language by using software AVR STUDIO 5.1?

Answer 1

Arduino Code – for interfacing 4 digit 7 segment display to arduino using shift register

Use following code for the common anode 7 segment display.

#include "Timer.h" //include timer library

Timer t; // create a timer object

long number = 0; //declare the variables

int first_digit = 0;

int second_digit = 0;

int third_digit = 0;

int fourth_digit = 0;

int timer_event = 0;

int CA_1 = 12;

int CA_2 = 11;

int CA_3 = 10;

int CA_4 = 9;

int clk = 6;

int latch = 5;

int data = 4;

int count = 0;

int digits[4] ;

int CAS[4] = {12, 11, 10, 9};

byte numbers[10] {B00000011, B10011111, B00100101, B00001101, B10011001, B01001001, B01000001, B00011111, B00000001, B00001001};

//byte combinations for each number 0-9

void setup() {

  Serial.begin(9600); //serial start and pin config

  pinMode(CA_1, OUTPUT);

  pinMode(CA_2, OUTPUT);

  pinMode(CA_3, OUTPUT);

  pinMode(CA_4, OUTPUT);

  pinMode(clk, OUTPUT);

  pinMode(latch, OUTPUT);

  pinMode(data, OUTPUT);

  digitalWrite(CA_1, LOW);

  digitalWrite(CA_2, LOW);

  digitalWrite(CA_3, LOW);

  digitalWrite(CA_4, LOW);

  Serial.println("please Enter a number from 0 to 9999");

}

void loop() {

  t.update(); //timer update

  if (Serial.available()) { // read from serial

    t.stop(timer_event); //stop timer if anything to read

    cathode_high(); // blank the screen

    String s = Serial.readString(); //read the serial value

    number = (long)s.toInt(); //convert it to int

    if (number > 9999) { //check the number is 0-9999

      Serial.println("Please Enter Number Between 0 - 9999");

    } else {

      break_number(number);

      timer_event = t.every(1, display_number); // start timer again

    }

  }

}

void break_number(long num) { // seperate the input number into 4 single digits

first_digit = num / 1000;

  digits[0] = first_digit;

  int first_left = num - (first_digit * 1000);

  second_digit = first_left / 100;

  digits[1] = second_digit;

  int second_left = first_left - (second_digit * 100);

  third_digit = second_left / 10;

  digits[2] = third_digit;

  fourth_digit = second_left - (third_digit * 10);

  digits[3] = fourth_digit;

}

void display_number() { //scanning

  cathode_high(); //black screen

  digitalWrite(latch, LOW); //put the shift register to read

  shiftOut(data, clk, LSBFIRST, numbers[digits[count]]); //send the data

  digitalWrite(CAS[count], HIGH); //turn on the relevent digit

  digitalWrite(latch, HIGH); //put the shift register to write mode

  count++; //count up the digit

  if (count == 4) { // keep the count between 0-3

    count = 0;

  }

}

void cathode_high() { //turn off all 4 digits

  digitalWrite(CA_1, LOW);

  digitalWrite(CA_2, LOW);

  digitalWrite(CA_3, LOW);

  digitalWrite(CA_4, LOW);

}

Use following code for the common cathode 7 segment display.

#include "Timer.h" //include timer library

Timer t; // create a timer object
long number = 0; //declare the variables
int first_digit = 0;
int second_digit = 0;
int third_digit = 0;
int fourth_digit = 0;
int timer_event = 0;
int CA_1 = 12;
int CA_2 = 11;
int CA_3 = 10;
int CA_4 = 9;
int clk = 6;
int latch = 5;
int data = 4;
int count = 0;
int digits[4] ;
int CAS[4] = {12, 11, 10, 9};
byte numbers[10] {B11111100, B01100000, B11011010, B11110010, B01100110, B10110110, B10111110, B11100000, B11111110, B11110110};
//byte combinations for each number 0-9
void setup() {
  Serial.begin(9600); //serial start and pin config
  pinMode(CA_1, OUTPUT);
  pinMode(CA_2, OUTPUT);
  pinMode(CA_3, OUTPUT);
  pinMode(CA_4, OUTPUT);
  pinMode(clk, OUTPUT);
  pinMode(latch, OUTPUT);
  pinMode(data, OUTPUT);
  digitalWrite(CA_1, HIGH);
  digitalWrite(CA_2, HIGH);
  digitalWrite(CA_3, HIGH);
  digitalWrite(CA_4, HIGH);
  Serial.println("please Enter a number from 0 to 9999");
}
void loop() {
  t.update(); //timer update
  if (Serial.available()) { // read from serial
    t.stop(timer_event); //stop timer if anything to read
    cathode_high(); // blank the screen
    String s = Serial.readString(); //read the serial value
    number = (long)s.toInt(); //convert it to int
    if (number > 9999) { //check the number is 0-9999
      Serial.println("Please Enter Number Between 0 - 9999");
    } else {
      break_number(number);
      timer_event = t.every(1, display_number); // start timer again
    }
  }
}
void break_number(long num) { // seperate the input number into 4 single digits
  first_digit = num / 1000;
  digits[0] = first_digit;
  int first_left = num - (first_digit * 1000);
  second_digit = first_left / 100;
  digits[1] = second_digit;
  int second_left = first_left - (second_digit * 100);
  third_digit = second_left / 10;
  digits[2] = third_digit;
  fourth_digit = second_left - (third_digit * 10);
  digits[3] = fourth_digit;
}
void display_number() { //scanning
  cathode_high(); //black screen
  digitalWrite(latch, LOW); //put the shift register to read
  shiftOut(data, clk, LSBFIRST, numbers[digits[count]]); //send the data
  digitalWrite(CAS[count], LOW); //turn on the relevent digit
  digitalWrite(latch, HIGH); //put the shift register to write mode
  count++; //count up the digit
  if (count == 4) { // keep the count between 0-3
    count = 0;
  }
}
void cathode_high() { //turn off all 4 digits
  digitalWrite(CA_1, HIGH);
  digitalWrite(CA_2, HIGH);
  digitalWrite(CA_3, HIGH);
  digitalWrite(CA_4, HIGH);
}

Important code lines are commented in the code. In this code you can send any number from 0 - 9999 through the serial monitor (refer the image given above).  We are using the arduino timer interrupts to switch between digits. The segments should be turn on and off for each number is stored in a byte array. In the loop() – serial values are read and converted  to int and then to long data types. Then this long data is broke in to single digits by break_number () method. Multiplexing is done by the timer class every() function and it calls display_number() method once every millisecond. This method use arduino shiftOut () function to send signals to shift register. Note how latch pin is turned LOW before we send data and turned HIGH after sending data. The function called cathode_high() is to turn off the screen.