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Introduction to OR Gate

A Logic Gate is an electronic device that implements a Boolean function, i.e., a logical operation is performed on one or more binary inputs to produce a single binary output. Logical operations are a fundamental part of digital circuits and are based on Boolean algebra. At any given time, the inputs and the output can have two conditions, true or false. True is expressed as 1 (high), and false as 0 (low). Depending on the type of Logic Gate and the combination of inputs, the output will differ.

Basic Logic Gates

There are three basic logic gates.

These are: AND, OR, NOT, also we have a few other gates derived from the basic gates NOR, NAND, XOR, XNOR

In the following sections, we look at the principle of OR Gate.

The OR Gate is an electronic circuit that produces a high output if any of its inputs are high. 

Symbol of OR Gate:

The OR Gate has inputs A and B and output Y. It implements the logical expression Y = A OR B / A +B 

Truth Table

Input AInput BOutput Y

Transistor Implementation of OR Gate

A two-input OR Gate is built with two Bipolar Junction Transistors (BJT). 

Circuit Diagram:

This circuit has inputs A and B connected to the base terminals of the two transistors. An LED, which is the output Y, is connected to the emitters of the transistors. +5V (Vcc) is supplied to the collector of the first transistor, which is in parallel with the second transistor. 


When both the switches are open, there is no current flowing through the transistors, and hence the output is LOW. In this state, the LED is OFF. When either of the switches is closed, the respective transistor turns ON. The current flows through the transistor and turns the output HIGH. In this state, the LED is ON. When both the switches are closed, both the transistors are ON, and the current flows through them. Hence the output is HIGH, and the LED turns ON.

For detailed instructions on the construction of OR Gate using transistors, visit: 

OR Gate using Transistors on a Breadboard

IC Package

OR Gates are available in IC Packages. The most common IC Package is 7432 IC. It is a QUAD 2-input OR Gate. It contains four independent Gates, each of which performs the logic OR function.

Diagram of IC7432

Witblox OR Gate

Witblox OR Gate is an addon Blox. It is a single OR Gate with two inputs and one output. You can connect any Input Blox to the OR Blox and build any OR-Logic-based applications.

How it Works

Example applications using OR Gate

Safety operation in machines

In a machine, if one or more than one parameter goes beyond a safe value, an alarm is triggered or the machine is turned off

Alarm circuit for car door system 

If one or more than one door of a car is open, an indicator or an alarm turns on. 

Additional Information

You can buy your Witblox OR Gate from here – Witblox OR Gate

Authored by Shreyas S Arbatti (13)

Witblox Maker and Electronics enthusiast

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