Random number generator circuit

Random number generators are fun circuits that has applications in games, lottery and so on. While most of the number generators are based on MCU, I thought to build it only using a 555 timer and IC 4026 along with a common cathode 7 segment display. It’s quite simple and easy to build more than that it is cost effective.


In this circuit the user is given a push button SW1 where it needs to be pressed for the number sequence to start. The number count goes from 0 to 9, with few modifications this circuit can be built to count from 0 to 99. When the button is pressed the circuit will increment the sequence at high speed and upon the release of this button you will have your random number.


1) IC 555
2) IC 4026
3) Common cathode 7 segment display
4) Resistors – 300 Ohms (7) and 1k (2)
5) Capacitors – 1uF


In this circuit 555 timer is wired as astable multivibrator where it generates square waves to feed the IC 4026. The frequency of this square wave depends upon the value of R1,R2 and C1. The formula to determine the output frequency is f = 1.44 / ( R2 + 2R1 ) C1 which gives a square wave of frequency 480hz as output.

You should keep the frequency output high so that the user will cannot judge the number sequence by any means. A button is placed in way of this signal which is feed to the IC 4026 when button is pressed. IC 4026 is a 7 segment decoder which takes clock signal input. The IC counts from 0 to 9 with each individual clock pulse and resets back to 0 once it hits 9. This cycle repeats itself with the incoming clock signal. The chip also decodes these counted values of 0 to 9 and lights up the 7 segment accordingly.

Since the speed of the clock signal is too fast the IC will count from 0 to 9 almost 48 times ( due to 480 hz clock signal ) in a matter of second. This makes the number appears in the 7 segment to be random and unpredictable in nature.


Random Number Generator
Random Number Generator
Version: 1
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By adding one more IC 4026 and 7 segment to the circuit you could make the circuit to count from 0 to 99. Almost all the connections remain same except you need to feed CO ( clock out ) from IC2 to IC3 Clock input. The 4026 gives out a CO signal once it reaches the count 9. Feeding this to IC3 will force it to increment one count with each cycle of counts from 0 to 9 in IC2. Therefore these two IC’s work together to count from 0 to 99.

Hope this circuit was useful to you. Do post your comments, suggestions and thoughts about this circuit in the below comment box. Happy DIY 🙂

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Frank Donald

Frank Donald

Junior Network Engineer at Tata Communications
Frank Donald is an Electronics and Communication Engineer who loves building stuff in his free time. Video games, blogging and programming are the things he loves most
Frank Donald

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