7-Segment LED Displays: Multiplexing

A matrix is created by passing pin numbers for the data, load, and clock pins. loop uses the write method to turn pixels on; the clar method turns the pixels off. write has three parameters: the first two identify the column and row (x and y) of an LED and the third  parameter (HIGH or LOW) turns the LED on or off.This Solution uses the popular MAX7221 LED driver chip to control four-digit commoncathode displays The MAX7221 provides a simpler solution  because it handles multiplexing and digit decoding in hardware.

/*

* SevenSegmentMpx sketch

*Shows numbers ranging from 0 through 9999 on a four-digit display

* This example displays the value of a sensor connected to an analog input

*/

// bits representing segments A through G (and decimal point) for numerals 0-9

const int numeral[10] = {

//ABCDEFG /dp

B11111100, // 0

B01100000, // 1

B11011010, // 2

B11110010, // 3

B01100110, // 4

B10110110, // 5

B00111110, // 6

B11100000, // 7

B11111110, // 8

B11100110, // 9

};

// pins for decimal point and each segment

// dp,G,F,E,D,C,B,A

const int segmentPins[] = { 4,7,8,6,5,3,2,9};

const int nbrDigits= 4; // the number of digits in the LED display

//dig 1 2 3 4

const int digitPins[nbrDigits] = { 10,11,12,13};

void setup()

{

for(int i=0; i < 8; i++)

pinMode(segmentPins[i], OUTPUT); // set segment and DP pins to output

for(int i=0; i < nbrDigits; i++)

pinMode(digitPins[i], OUTPUT);

}

void loop()

{

int value = analogRead(0);

showNumber(value);

}

void showNumber( int number)

{

if(number == 0)

showDigit( 0, nbrDigits-1) ; // display 0 in the rightmost digit

else

{

// display the value corresponding to each digit

// leftmost digit is 0, rightmost is one less than the number of places

for( int digit = nbrDigits-1; digit >= 0; digit--)

{

if(number > 0)

{

showDigit( number % 10, digit) ;

number = number / 10;

}

}

}

}

// Displays given number on a 7-segment display at the given digit position

void showDigit( int number, int digit)

{

digitalWrite( digitPins[digit], HIGH );

for(int segment = 1; segment < 8; segment++)

{

boolean isBitSet = bitRead(numeral[number], segment);

// isBitSet will be true if given bit is 1

isBitSet = ! isBitSet; // remove this line if common cathode display

digitalWrite( segmentPins[segment], isBitSet);

}

delay(5);

digitalWrite( digitPins[digit], LOW );

}