Build a OR Gate From Transistors

About: “Let the future tell the truth, and evaluate each one according to his work and accomplishments. The present is theirs; the future, for which I have really worked, is mine.” Nikola Tesla

In this guide I will show you how to build an OR gate with two transistors.

For a basic detail of how the NPN transistor is being used in this project, please see the intro message to my AND gate instructable.

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Step 1: Parts List

To build a logic OR gate you are going to need the following parts:

  • 1x Breadboard
  • 1x LED (Any color)
  • 1x 1K Ohm resistor
  • 2x 10K Ohm resistors
  • 2x NPN Transistors (I used the 2N2222)
  • 2x N.O. Push buttons
  • 6x Various length wires/Jumper wires

You will also need to know how to build a circuit based off of a schematic.

Step 2: Schematic / Truth Table

First construct the circuit from the schematic in the above image. (Please excuse my terrible drawing skills..)

Now I will show you the truth table:

0  0  0
0  1  1
1  0  1
1  1  1

This logic gate is very simple, the output will only be ON (1) if A is ON (1), B is ON (1), or both are ON (1). Otherwise it will be OFF (0).



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    3 Discussions


    4 years ago on Introduction

    If on when both a and b is on, then it is an and gate for that condition


    Reply 4 years ago on Introduction

    Thank you :)

    My plan is to show how to make the basic logic gates, then build up to bigger things like adders and d-type flip flops. The end goal will be a guide on building an entire CPU out of transistor logic gates (except ROM and SRAM) based off of a design I am currently working on.