7-segment display code

Question 1

What is the meaning ofBitSet = bitRead(numeral[number], segment);?

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,Aconst 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 offvoid 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);  }}

Question 2

Do you now about chips like the Max7219? It will help you handle a number of 7 segment displays (up to 8).

Question 3

bitRead(x, y) takes a valuex, and looks atbit numbery.

So, if:

y is the number2;

x is53 (binary number00110101)

it looks at bit #2. Bits are counted from theright starting at0 - I have indicated the bit in question above.

So,bitRead(53, 2) would return1, since bit #2 in 53 is a1.

In the above program, the clever programmer has coded whether to light or not light the LED for each segment of the display in a single byte for each possible number to display. The digit8 has all seven of its LEDs lit up, so you'd expect the encoding for8 to have lots of binary1s in it - and sure enough, it does (B11111110)! And the digit7 has only three segments lit up, so you'd expect only 3 bits to be set. Sure enough,B11100000.

The comment at the top describes what each of the bits represent - the last bit is the decimal point, which is never set...

John Burger 1,8851 gold badge14 silver badges24 bronze badges · Answer 1 · 2016-09-09 13:13:53Z

bitRead(x, y) takes a valuex, and looks atbit numbery.

So, if:

y is the number2;

x is53 (binary number00110101)

it looks at bit #2. Bits are counted from theright starting at0 - I have indicated the bit in question above.

So,bitRead(53, 2) would return1, since bit #2 in 53 is a1.

In the above program, the clever programmer has coded whether to light or not light the LED for each segment of the display in a single byte for each possible number to display. The digit8 has all seven of its LEDs lit up, so you'd expect the encoding for8 to have lots of binary1s in it - and sure enough, it does (B11111110)! And the digit7 has only three segments lit up, so you'd expect only 3 bits to be set. Sure enough,B11100000.

The comment at the top describes what each of the bits represent - the last bit is the decimal point, which is never set...

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