OR Gate (74LS32)

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Building an OR Gate (74LS32)

Continuing our journey through digital logic, it’s time to explore the OR gate, another fundamental building block of electronics.
In this post, we’ll build an OR Gate using the 74LS32 TTL IC, light it up with an LED, and see how its logic behaves.

How the OR Gate Works

An OR gate outputs HIGH if any of its inputs are HIGH.
That means even if only one input is ON, the output will be ON too.


Inside the 74LS32 are four independent 2-input OR gates, so you can build several circuits or expand your experiments later.

Pinout (74LS32)

Each set of three pins (A, B, Y) is one Or gate.

What You’ll Need

  • 1 × 74LS32 IC (Quad 2-input OR gate)

  • Breadboard + jumper wires

  • 2 × push buttons (or jumper wires for manual inputs)

  • 2 × 10 kΩ resistors (pull-down resistors for inputs)

  • 1 × 330 Ω resistor (for the LED)

  • 1 × LED (any colour)

  • 5 V power supply (or Arduino 5 V pin)

Circuit Diagram

Wiring the Circuit

  1. Connect Vcc (pin 14) to +5 V and GND (pin 7) to ground.

  2. Use two push buttons or jumper wires for your inputs (A & B). Connect one side of each push button to +5v and the otherside of one to either Pin 1(A) or Pin 2(B) of the IC.


  3. Each input goes through a 10 kΩ pull-down resistor to GND, so it stays LOW when not pressed.

  4. Connect output Y (pin 3) to a 330 Ω resistor → LED → GND.

  5. Power it up and press the buttons:

    • If either or both buttons are pressed, the LED lights up!

Understanding It Visually

No buttons pressed: both inputs LOW → LED OFF

Only A pressed: one HIGH, one LOW → LED ON
Only B pressed: one HIGH, one LOW → LED ON
Both pressed: both HIGH → LED ON

You’ll notice even one HIGH input turns the LED ON. That’s the OR logic in action.

Try This

  • Chain it with your NOT gate to make a NOR gate (simply connect the OR output into a NOT input).

  • Add LEDs on each input and output to visualise logic states side by side.

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