AND Gate (74LS08)

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Building an AND Gate (74LS08)

If you’ve been following along with the NOT gate project, this is the perfect next step.
The AND gate is another fundamental building block of digital logic, it outputs HIGH only when all inputs are HIGH.

In this post, we’ll build one using the 74LS08 TTL IC and demonstrate it using an LED.

What You’ll Need

  • 1 × 74LS08 IC (Quad 2-input AND gates)

  • Breadboard + jumper wires

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

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

  • 1 × 330 Ω resistor (for LED)

  • 1 × LED (any colour)

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

 How the AND Gate Works

An AND gate has two inputs and one output.

So the output goes HIGH only when both A and B are HIGH.

Inside the 74LS08, there are four of these gates, this is great for testing or chaining into larger circuits.

 Pinout (74LS08)

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

Circuit Diagram

Wiring It Up

  1. Connect pin 14 to +5 V and pin 7 to ground.

  2. Use pins 1 (A) and 2 (B) as your two inputs, connect a push button to each pin from +5V.

  3. Add 10 kΩ pull-down resistors from pins 1 and 2 to ground.

  4. Connect pin 3 to an LED though a 330 Ω resistor for the output.

When you press both buttons, the LED lights up and your AND gate is in action!

Understanding It Visually

  • No buttons pressed: both inputs LOW → LED OFF

  • Only A pressed: one HIGH, one LOW → LED OFF

  • Only B pressed: one HIGH, one LOW → LED OFF

  • Both pressed: both HIGH → LED ON

Try Expanding It

Once it’s working:

  • Combine with a 74LS04 NOT gate to make NAND logic.

  • Chain multiple ANDs together to form enable circuits.

  • Use one LED per gate to see how multiple gates behave simultaneously.

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