Implementation of four 7-Segment LED display multiplexing with 8051 microcontroller

7-segment LED display are the widely used displays in many applications that can display any character or digital value. We have already discussed the 7-segment concept in our previous post which defines it as the combination of 8 LEDs forming "8" display and divided as the common cathode and common anode.

Now, learn the concept of multiplexing by which you can connect many 7-segment displays to a single port of 8051 microcontroller. Earlier we discussed about the 7-segment up counter display in which 3 7-segments are connected to 3 different ports and up counter is running from 0-999. But, it had limitation. You can not connect many 7-segments to a single port.

Multiplexing of 7-segment:

- In the above diagram you can see how i have connected the 4 7-segment display to the port P2 of 8051 microcontroller. It is a schematic diagram which i have drawn in Proteus ISIS professional. But, in practical you can implement the same concept. Use 8 pins of any port of microcontroller and connect the single pin to same pin of all 7-segment LED display and Hence, the multiplexing has been implemented.

Code:

#include"REGx52.h"
#define seg_data P2
sbit seg1=P0^1;
sbit seg2=P0^2;
sbit seg3=P0^3;
int ones=0,tens=0,hundreds=0,l;
void display_digit(int );
void delay();

void main()
{
seg1=seg2=seg3=1;
while(l<=999)
{
ones=l%10;
tens=(l/10)%10;
hundreds=(l/100);
display_digit(ones);
seg1=0;
delay();
seg1=1;

display_digit(tens);
seg2=0;
delay();
seg2=1;

display_digit(hundreds);
seg3=0;
delay();
seg3=1;
l++;
}
}

void delay()
{
long int k;
for(k=0;k<1000;k++);
}
void display_digit(int c)
{
switch(c)
{
case 0:
seg_data=0xbf;
break;
case 1:
seg_data=0x06;
break;
case 2:
seg_data=0x5b;
break;
case 3:
seg_data=0x4f;
break;
case 4:
seg_data=0x66;
break;
case 5:
seg_data=0x6d;
break;
case 6:
seg_data=0x7d;
break;
case 7:
seg_data=0x07;
break;
case 8:
seg_data=0x7f;
break;
case 9:
seg_data=0x6f;
break;
}
}

Explanation of code:

- It is similar as we write up counter. Use the binary to hexadecimal conversion concept to extract MSB and LSB digits for ones and thousands place. Now, use digital_display() function to display the value by passing it as an argument. This argument value is matched with the digital_display() passed value and then, switch case is taken through which the called value is displayed over 7-segment.