Project 18 4-digit LED Segment Display

1. Introduction In this experiment, we use an Arduino to drive a common anode, 4-digit, 7-segment LED display. For LED display, current-limiting resistors are indispensable. There are two wiring methods for Current-limiting resistor.

One is to connect one resistor for each anode, 4 in totals for d1-d4 anode. An advantage for this method is that it requires fewer resistors, only 4. But it cannot maintain consistent brightness.

Another method is to connect one resistor to each pin. It guarantees consistent brightness, but requires more resistors.

In this experiment, we use 8 220Ω resistors (we use 220Ω resistors because no 100Ω resistor available. If you use 100Ω, the displaying will be more brighter).

For 4-digit displays, there are 12 pins in total. When you place the decimal point downward (see below photo position), the pin on the lower left part is referred to 1, the upper left part 12.

2. Manual for LED segment display

3. Connection for REV4

4. Connection for 2560 R3

5. Sample Code

// display 1234 
	// select pin for cathode
	int a = 1;
	int b = 2;
	int c = 3;
	int d = 4;
	int e = 5;
	int f = 6;
	int g = 7;
	int dp = 8;
	// select pin for anode
	int d4 = 9;
	int d3 = 10;
	int d2 = 11;
	int d1 = 12;
	// set variable
	long n = 1230;
	int x = 100;
	int del = 55;  // fine adjustment for clock
	 
	void setup()
	{
	  pinMode(d1, OUTPUT);
	  pinMode(d2, OUTPUT);
	  pinMode(d3, OUTPUT);
	  pinMode(d4, OUTPUT);
	  pinMode(a, OUTPUT);
	  pinMode(b, OUTPUT);
	  pinMode(c, OUTPUT);
	  pinMode(d, OUTPUT);
	  pinMode(e, OUTPUT);
	  pinMode(f, OUTPUT);
	  pinMode(g, OUTPUT);
	  pinMode(dp, OUTPUT);
	}

void loop()
{
 Display(1, 1);
 Display(2, 2);
 Display(3, 3);
 Display(4, 4);
}

void WeiXuan(unsigned char n)//
{
    switch(n)
    {
		case 1: 
          digitalWrite(d1,LOW);
          digitalWrite(d2, HIGH);
          digitalWrite(d3, HIGH);
          digitalWrite(d4, HIGH);   
          break;
	 	case 2: 
          digitalWrite(d1, HIGH);
          digitalWrite(d2, LOW);
          digitalWrite(d3, HIGH);
          digitalWrite(d4, HIGH); 
	      break;
	   case 3: 
	    digitalWrite(d1,HIGH);
 	    digitalWrite(d2, HIGH);
	    digitalWrite(d3, LOW);
	    digitalWrite(d4, HIGH); 
	    break;
	   case 4: 
           digitalWrite(d1, HIGH);
           digitalWrite(d2, HIGH);
           digitalWrite(d3, HIGH);
           digitalWrite(d4, LOW); 
	   	   break;
        default :
           digitalWrite(d1, HIGH);
	   	   digitalWrite(d2, HIGH);
	   	   digitalWrite(d3, HIGH);
	   	   digitalWrite(d4, HIGH);
           break;
	 }
}

void Num_0()
{
  digitalWrite(a, HIGH);
  digitalWrite(b, HIGH);
  digitalWrite(c, HIGH);
  digitalWrite(d, HIGH);
  digitalWrite(e, HIGH);
  digitalWrite(f, HIGH);
  digitalWrite(g, LOW);
  digitalWrite(dp,LOW);
}

void Num_1()
{
  digitalWrite(a, LOW);
  digitalWrite(b, HIGH);
  digitalWrite(c, HIGH);
  digitalWrite(d, LOW);
  digitalWrite(e, LOW);
  digitalWrite(f, LOW);
  digitalWrite(g, LOW);
  digitalWrite(dp,LOW);
}

void Num_2()
{
  digitalWrite(a, HIGH);
  digitalWrite(b, HIGH);
  digitalWrite(c, LOW);
  digitalWrite(d, HIGH);
  digitalWrite(e, HIGH);
  digitalWrite(f, LOW);
  digitalWrite(g, HIGH);
  digitalWrite(dp,LOW);
}

void Num_3()
{
  digitalWrite(a, HIGH);

  digitalWrite(b, HIGH);
  digitalWrite(c, HIGH);
  digitalWrite(d, HIGH);
  digitalWrite(e, LOW);
  digitalWrite(f, LOW);
  digitalWrite(g, HIGH);
  digitalWrite(dp,LOW);
}

void Num_4()
{
  digitalWrite(a, LOW);
  digitalWrite(b, HIGH);
  digitalWrite(c, HIGH);
  digitalWrite(d, LOW);
  digitalWrite(e, LOW);
  digitalWrite(f, HIGH);
  digitalWrite(g, HIGH);
  digitalWrite(dp,LOW);
}

void Num_5()
{
  digitalWrite(a, HIGH);
  digitalWrite(b, LOW);
  digitalWrite(c, HIGH);
  digitalWrite(d, HIGH);
  digitalWrite(e, LOW);
  digitalWrite(f, HIGH);
  digitalWrite(g, HIGH);
  digitalWrite(dp,LOW);
}

void Num_6()
{
  digitalWrite(a, HIGH);
  digitalWrite(b, LOW);
  digitalWrite(c, HIGH);
  digitalWrite(d, HIGH);
  digitalWrite(e, HIGH);
  digitalWrite(f, HIGH);
  digitalWrite(g, HIGH);
  digitalWrite(dp,LOW);
}

void Num_7()
{
  digitalWrite(a, HIGH);
  digitalWrite(b, HIGH);
  digitalWrite(c, HIGH);
  digitalWrite(d, LOW);
  digitalWrite(e, LOW);
  digitalWrite(f, LOW);
  digitalWrite(g, LOW);
  digitalWrite(dp,LOW);
}

void Num_8()
{
  digitalWrite(a, HIGH);
  digitalWrite(b, HIGH);
  digitalWrite(c, HIGH);
  digitalWrite(d, HIGH);
  digitalWrite(e, HIGH);
  digitalWrite(f, HIGH);
  digitalWrite(g, HIGH);
  digitalWrite(dp,LOW);
}

void Num_9()
{
  digitalWrite(a, HIGH);
  digitalWrite(b, HIGH);
  digitalWrite(c, HIGH);
  digitalWrite(d, HIGH);
  digitalWrite(e, LOW);
  digitalWrite(f, HIGH);
  digitalWrite(g, HIGH);
  digitalWrite(dp,LOW);
}

void Clear()  // clear the screen
{
  digitalWrite(a, LOW);
  digitalWrite(b, LOW);
  digitalWrite(c, LOW);
  digitalWrite(d, LOW);

  digitalWrite(e, LOW);
  digitalWrite(f, LOW);
  digitalWrite(g, LOW);
  digitalWrite(dp,LOW);
}

void pickNumber(unsigned char n)// select number
{
  switch(n)
  {
   case 0:Num_0();
   break;
   case 1:Num_1();
   break;
   case 2:Num_2();
   break;
   case 3:Num_3();
   break;
   case 4:Num_4();
   break;
   case 5:Num_5();
   break;
   case 6:Num_6();
   break;
   case 7:Num_7();
   break;
   case 8:Num_8();
   break;
   case 9:Num_9();
   break;
   default:Clear();
   break; 
  }
}

void Display(unsigned char x, unsigned char Number)//  take x as coordinate and display number
{
  WeiXuan(x);
  pickNumber(Number);
  delay(1);
  Clear() ; // clear the screen
}

Result: Download the above code to the controller board and see the result.The experiment result displays 1234 on the LED display.

Note: if it’s not displaying correctly, check the wiring. Thank you!