Driving a 7-Segment LED Display

The segments to be lit for each numeral are held in the array called numeral. There isone byte per numeral where each bit in the byte represents one of seven segments .The array called segmentPins holds the pins associated with each segment. TheshowDigit function checks that the number ranges from zero to 9, and if valid, looks ateach segment bit and turns on the segment if the bit is set. Apin is set HIGH when turning on a segment on a commoncathode display, and it’s set LOW when turning on a segment on a common anode

display. The code here is for a common anode display, so it inverts the value as follows:

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

CODE:

The following sketch displays numerals from zero to nine on a single-digit, 7-segmentdisplay. The output is produced by turning oncombinations of segments that represent the numerals:

/*

* SevenSegment sketch

* Shows numerals ranging from 0 through 9 on a single-digit display

* This example counts seconds from 0 to 9

*/

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

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

void setup()

{

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

{

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

}

}

void loop()

{

for(int i=0; i <= 10; i++)

{

showDigit(i);

delay(1000);

}

// the last value if i is 10 and this will turn the display off

delay(2000); // pause two seconds with the display off

}

// Displays a number from 0 through 9 on a 7-segment display

// any value not within the range of 0-9 turns the display off

void showDigit( int number)

{

boolean isBitSet;

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

{

if( number < 0 || number > 9){

isBitSet = 0; // turn off all segments

}

else{

// isBitSet will be true if given bit is 1

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

}

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

digitalWrite( segmentPins[segment], isBitSet);

}

}