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Arduino UNO R3/MEGA 2560 R3 Project 18: 4-digit LED Segment Display

Posted by Fiona Su on

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 method for Current-limiting resistor.

One is to connect one resistor for each anode, 4 in total for d1-d4 anode. An advantage for this method is that it requires fewer resistors, only 4. But it cannot maintain consistent brightness, 1 the brightest, 8, the least bright.
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 is more brighter).

Connection

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 refer to as 1, the upper left part 12.

Manual for LED segment display:

Connection for REV4:

Connection for 2560 R3:

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.
It will display the number 1234.
Note: if it’s not displaying correctly, check the wiring.
Thank you.