Random Number generator using 8051 Microcontroller

Random Number generators are something which is used to draw out a random number and use it for a specified purpose. The purpose may differ it might be lottery draw , competition or whatever it may be the above generator using 8051 will do a pretty good job also the complexity level of the program is very simple. Here is a simple random number generator using 8051 which will serve the purpose well at low cost and requires less programming skill.

IC 74LS48:

The IC 74LS48 or 7448 is a simple BCD to 7 segment decoder which was used to reduce the usage of pins dedicated to the 7 segment display. It consists of 4 input pins namely 1,2,3,4 which is used to feed 4 bit data input to the IC. The fed 4 bit input binary data in turn decoded by the IC and output is obtained from the pins a, b ….. f  which is connected to the corresponding pins of the 7 segment display. This will display the correct digit in the 7 segment display.


In the above design i have used two 7448 IC to interface two 7 segments in a single port, this will save the pin usage from the microcontroller. You can also go for direct interfacing of  a 7 segment with a dedicated port if you don’t have 7448 IC in your possession. 

Interrupt 0 feature of the Microcontroller was used here, therefore a simple push button was interfaced with the pin INT0 pin of the 8051 controller. Reset button was used with the pin 9 to reset the operation and start running the program from the beginning.


  • Initially the number keeps running from 0 to 99 in the display at high speed in a loop, so it will barely visible to human eye. 
  • Pressing the interrupt button fetches the random number and displays it in the 7 segment display.
  • The the reset button should be pressed to initialize the program and counting again.


This code was built using Keil Uvision 4 
int a,b;
void delay();
void main()
  IE=0x81;                   //External interrupt activation
  for(a=0;a<=9;a++)     //Number generation
void delay()
  int i;

void extr0(void) interrupt 0     //Subroutine EX0 with interrupt number '0'


  • Resistors for 7 segment are omitted for the simplicity of the schematic diagram, hook up a 470 ohm resistor to each pins connecting from 74LS48 to 7 segment pins.

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without reset the 8051 can we change the number ??what is change in code if..once a number was displayed than that number will display after 99 time later…or if we reset the controller…plz tell me