Problem in the display of 20 7-segment LEDs using Arduino Mega2560

nyal · September 14, 2023, 6:06am

I'm using Arduino Mega 2560 to light up 20 7-segment LEDs. In addition I'm multiplexing 20 7-segment LEDs. I want it to display 0-9 in digit1 to digit10 and 0-9 in digit11 to digit20. My problem right it is displaying incorrect numbers.

How should I fix this? This is my code.

#define SLOW_CLOCK

int time = 1000;

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

int digit1 = 13;
int digit2 = 12;
int digit3 = 11;
int digit4 = 10;
int digit5 = 28;
int digit6 = 26;
int digit7 = 25;
int digit8 = 27;
int digit9 = 29;
int digit10 = 31; 
int digit11 = 33;
int digit12 = 24;
int digit13 = 22;
int digit14 = 23;
int digit15 = 35;
int digit16 = 37;
int digit17 = 39;
int digit18 = 41;
int digit19 = 43;
int digit20 = 45;

// Define arrays to hold the numbers to display on digits 1 to 10 and digits 11 to 20
int numbers1to10[10] = {
  0, 1, 2, 3, 4, 5, 6, 7, 8, 9
};

int numbers11to20[10] = {
  0, 1, 2, 3, 4, 5, 6, 7, 8, 9
};


void choose_digit(char num) {
  switch(num){
    default:
    // 0 default value
      digitalWrite(a, HIGH);
      digitalWrite(b, HIGH);
      digitalWrite(c, HIGH);
      digitalWrite(d, HIGH);
      digitalWrite(e, HIGH);
      digitalWrite(f, HIGH);
      digitalWrite(g, LOW);
      break;

    case 1:
      digitalWrite(a, LOW);
      digitalWrite(b, HIGH);
      digitalWrite(c, HIGH);
      digitalWrite(d, LOW);
      digitalWrite(e, LOW);
      digitalWrite(f, LOW);
      digitalWrite(g, LOW);
      break;

    case 2:
      digitalWrite(a, HIGH);
      digitalWrite(b, HIGH);
      digitalWrite(c, LOW);
      digitalWrite(d, HIGH);
      digitalWrite(e, HIGH);
      digitalWrite(f, LOW);
      digitalWrite(g, HIGH);
      break;

    case 3:
      digitalWrite(a, HIGH);
      digitalWrite(b, HIGH);
      digitalWrite(c, HIGH);
      digitalWrite(d, HIGH);
      digitalWrite(e, LOW);
      digitalWrite(f, LOW);
      digitalWrite(g, HIGH);
      break;
    
    case 4:
      digitalWrite(a, LOW);
      digitalWrite(b, HIGH);
      digitalWrite(c, HIGH);
      digitalWrite(d, LOW);
      digitalWrite(e, LOW);
      digitalWrite(f, HIGH);
      digitalWrite(g, HIGH);
      break;
    
    case 5:
      digitalWrite(a, HIGH);
      digitalWrite(b, LOW);
      digitalWrite(c, HIGH);
      digitalWrite(d, HIGH);
      digitalWrite(e, LOW);
      digitalWrite(f, HIGH);
      digitalWrite(g, HIGH);
      break;

    case 6:
      digitalWrite(a, HIGH);
      digitalWrite(b, LOW);
      digitalWrite(c, HIGH);
      digitalWrite(d, HIGH);
      digitalWrite(e, HIGH);
      digitalWrite(f, HIGH);
      digitalWrite(g, HIGH);
      break;

    case 7:
      digitalWrite(a, HIGH);
      digitalWrite(b, HIGH);
      digitalWrite(c, HIGH);
      digitalWrite(d, LOW);
      digitalWrite(e, LOW);
      digitalWrite(f, LOW);
      digitalWrite(g, LOW);
      break;

    case 8:
      digitalWrite(a, HIGH);
      digitalWrite(b, HIGH);
      digitalWrite(c, HIGH);
      digitalWrite(d, HIGH);
      digitalWrite(e, HIGH);
      digitalWrite(f, HIGH);
      digitalWrite(g, HIGH);
      break;

    case 9:
      digitalWrite(a, HIGH);
      digitalWrite(b, HIGH);
      digitalWrite(c, HIGH);
      digitalWrite(d, HIGH);
      digitalWrite(e, LOW);
      digitalWrite(f, HIGH);
      digitalWrite(g, HIGH);
      break;
  }
}

void setup()
{

#ifdef SLOW_CLOCK
  noInterrupts();
  CLKPR = _BV(CLKPCE);  // enable change of the clock prescaler
  CLKPR = _BV(CLKPS0);  // divide frequency by 2
  interrupts();
#endif;

  pinMode(digit1, OUTPUT);
  pinMode(digit2, OUTPUT);
  pinMode(digit3, OUTPUT);
  pinMode(digit4, OUTPUT);
  pinMode(digit5, OUTPUT);
  pinMode(digit6, OUTPUT);
  pinMode(digit7, OUTPUT);
  pinMode(digit8, OUTPUT);
  pinMode(digit9, OUTPUT);
  pinMode(digit10, OUTPUT);
  pinMode(digit11, OUTPUT);
  pinMode(digit12, OUTPUT);
  pinMode(digit13, OUTPUT);
  pinMode(digit14, OUTPUT);
  pinMode(digit15, OUTPUT);
  pinMode(digit16, OUTPUT);
  pinMode(digit17, OUTPUT);
  pinMode(digit18, OUTPUT);
  pinMode(digit19, OUTPUT);
  pinMode(digit20, OUTPUT);

  pinMode(a, OUTPUT);
  pinMode(b, OUTPUT);
  pinMode(c, OUTPUT);
  pinMode(d, OUTPUT);
  pinMode(e, OUTPUT);
  pinMode(f, OUTPUT);
  pinMode(g, OUTPUT);

  Serial.begin(9600);

}


void pick_digit(int digit) {

  switch(digit) {
    case 1: digitalWrite(digit20, HIGH);
    digitalWrite(digit1, LOW); break;

    case 2: digitalWrite(digit1, HIGH);
    digitalWrite(digit2, LOW); break;

    case 3: digitalWrite(digit2, HIGH);
    digitalWrite(digit3, LOW); break;

    case 4: digitalWrite(digit3, HIGH);
    digitalWrite(digit4, LOW); break;

    case 5: digitalWrite(digit4, HIGH);
    digitalWrite(digit5, LOW); break;

    case 6: digitalWrite(digit5, HIGH);
    digitalWrite(digit6, LOW); break;

    case 7: digitalWrite(digit6, HIGH);
    digitalWrite(digit7, LOW); break;

    case 8: digitalWrite(digit7, HIGH);
    digitalWrite(digit8, LOW); break;

    case 9: digitalWrite(digit8, HIGH);
    digitalWrite(digit9, LOW); break;

    case 10: digitalWrite(digit9, HIGH);
    digitalWrite(digit10, LOW); break;

    case 11: digitalWrite(digit10, HIGH);
    digitalWrite(digit11, LOW); break;

    case 12: digitalWrite(digit11, HIGH);
    digitalWrite(digit12, LOW); break;

    case 13: digitalWrite(digit12, HIGH);
    digitalWrite(digit13, LOW); break;

    case 14: digitalWrite(digit13, HIGH);
    digitalWrite(digit14, LOW); break;

    case 15: digitalWrite(digit14, HIGH);
    digitalWrite(digit15, LOW); break;

    case 16: digitalWrite(digit15, HIGH);
    digitalWrite(digit16, LOW); break;

    case 17: digitalWrite(digit16, HIGH);
    digitalWrite(digit17, LOW); break;

    case 18: digitalWrite(digit17, HIGH);
    digitalWrite(digit18, LOW); break;

    case 19: digitalWrite(digit18, HIGH);
    digitalWrite(digit19, LOW); break;

    case 20: digitalWrite(digit19, HIGH);
    digitalWrite(digit20, LOW); break;

  }
}


void seven_segment() {
  // Loop through digits 1 to 20
  for (int i = 1; i <= 20; i++) {
    // Determine the array index based on the current digit
    int index = (i <= 10) ? i - 1 : i - 11;

    choose_digit((i <= 10) ? numbers1to10[index] : numbers11to20[index]);
    pick_digit(i);

  }

}

void loop() {

  // Display the number on the seven segment display
  seven_segment();

}

This is the output.

lastchancename · September 14, 2023, 6:22am

You’re trying to do it the right way, but making it hard on yourself.

use arrays well, and functions to soften and simplify your code.

paulpaulson · September 14, 2023, 6:31am

Hello nyal

Welcome to the worldbest Arduino forum ever.

Take some time and investigate the correct ussage of the index-value for the arrays used.

Have a nice day and enjoy coding in C++.

6v6gt · September 14, 2023, 7:08am

nyal:

// Determine the array index based on the current digit
    int index = (i <= 10) ? i - 1 : i - 11;
    choose_digit((i <= 10) ? numbers1to10[index] : numbers11to20[index]);
    pick_digit(i);

You should probably wrap the above with a timer something like:

static uint32_t lastLoopAtMs = 0; // static initialized only once 
if ( millis() - lastLoopAtMs > 3 ) {  // adjust to minimise flicker
   lastLoopAtMs = millis() ;
  // Determine the array index based on the current digit
   int index = (i <= 10) ? i - 1 : i - 11;
   choose_digit((i <= 10) ? numbers1to10[index] : numbers11to20[index]); 
   pick_digit(i); 
}

to allow each digit position to display for a few milliseconds.

GolamMostafa · September 14, 2023, 8:10am

I would like to suggest you to proceed with a 2-digit cc-type multiplexed display unit (Fig-1) and then increase the digits one at a time. If you follow this procedure, you will be able to find the problem quicky whether it is in hardware or software. (A multiplxed display unit is built by shorting together the identical segment pins and leaving the cc-pins isolated.)

Figure-1:

Untested Sketch:
(This sketch can be extended to handle 8 display devices: DP0-DP7. It can also be extended to handle all 20 display devices.)

byte ccTable[] =  //array holding the cc-codes for digits: 0 - F
{
  0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07,
  //0    1    2     3     4     5     6     7
  0x7F, 0x6F, 0x77, 0x7C, 0x39, 0x5E, 0x79, 0x71
}; //8     9     A      B     C     D     E    F


void setup()
{
  for (int i = 22; i < 30; i++) //PA0-PA7 are output lines
  {
    pinMode(i, OUTPUT);
  }
  DDRB = 0xFF;  //PB0-PB7 are output lines; initialized using Data Direction Register
  DDRC = 0xFF;  //PC0-PC7 are output
  DDRL = 0b00001111;  //PL0-PL3 are output
}

void loop() //show: 0 at DP0, 1 at DP1
{
  for(int i = 0; i < 2; i++)
  {
    PORTB = 0xFF;   //signal lines (PB0-PB7) for (cc0-cc7) pins of (DP0-DP7) are OFF
    PORTA = ccTable[i];  //cc-code of 0 and then of 1
    bitClear(PORTB, i);   //only cc0-pin is low; 0 appears on DP0; and son on.... 
    delay(10);
  }
}

6v6gt · September 14, 2023, 9:56am

This topic has now appeared on StackExchange:

It'll be interesting to compare the responses.

david_2018 · September 14, 2023, 10:31am

You will see that referred to as "ghosting", where the digit will appear dimly on an adjacent display.

I expect someone there will point out that with this many digits, it might be better to multiplex the segments instead of the digits, that way the refresh rate would be 50Hz x 7 = 350 instead of 50Hz x 20 = 1000. That would require transistors to handle the current of 20 segments lit simultaneously.

// Define arrays to hold the numbers to display on digits 1 to 10 and digits 11 to 20
int numbers1to10[10] = {
  0, 1, 2, 3, 4, 5, 6, 7, 8, 9
};

int numbers11to20[10] = {
  0, 1, 2, 3, 4, 5, 6, 7, 8, 9
};

Why two arrays to hold the numbers being displayed?

#ifdef SLOW_CLOCK
  noInterrupts();
  CLKPR = _BV(CLKPCE);  // enable change of the clock prescaler
  CLKPR = _BV(CLKPS0);  // divide frequency by 2
  interrupts();
#endif;

What possible reason would you have for slowing down the clock? The refresh rate is going to consume a considerable amount of processor time to begin with, if you have any plans to add code outside of the display itself then the clock needs to run at full speed.

6v6gt · September 14, 2023, 10:35am

Also, a photograph of a rapidly multiplexing display, this one currently runs uncontrolled at loop speed, will not necessarily match the persistence of vision qualities of the human eye. In the worst case, it will show only one digit position lit and the rest blank. A longer exposure will show all segments on all displays lit with possibly some differences in intensity.

6v6gt · September 14, 2023, 3:23pm

In the mean time the cross post has been dealt with but not through my endeavours.

system · March 12, 2024, 3:24pm

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.

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Problem in the display of 20 7-segment LEDs using Arduino Mega2560

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