Welcome back to another episode! 🚀
In today’s tutorial, I’ll walk you through how to convert a Boolean expression into a logic circuit using NI Multisim. We’ll cover everything step by step – from adding basic components like switches and LEDs to building complete Boolean expressions using AND, OR, and NOT gates.




Step 1: Getting Started with Multisim

Before we dive in, make sure you have Multisim downloaded and installed. (I’ll upload a separate video showing you how to download and install it.)

Once you open Multisim, we’re going to set up the basic testing circuit with:

  • A DC source (5V battery)

  • A ground connection

  • A switch

  • An LED

This will allow us to test simple ON/OFF logic before moving into more complex Boolean expressions.


Step 2: Testing a Switch with an LED

  1. Go to Place Component → Sources → Power Sources, then select a DC Power Source (5V).

  2. Add a Ground connection.

  3. Place a Switch (you can toggle it with your keyboard for easier control).

  4. Place an LED (choose any color – we’ll use red for simplicity).

Now connect everything:

  • Battery → Switch → LED → Ground.

👉 When the switch is closed, the LED turns ON (logic 1).
👉 When the switch is open, the LED turns OFF (logic 0).

This is the most basic representation of logic in circuits.


Step 3: Creating Multiple Inputs (A, B, C, D)

Since our Boolean expression has four input variables (A, B, C, D), we’ll create four switches:

  • Switch A (toggle with key 1)

  • Switch B (toggle with key 2)

  • Switch C (toggle with key 3)

  • Switch D (toggle with key 4)

Each switch represents one input line to our Boolean function.


Step 4: Adding NOT Gates (Inverters)

In the Boolean expression, the dash (′) indicates a NOT operation. For example, A′ means “NOT A.”

To create NOT gates in Multisim:

  1. Go to Place Component → All Groups → Logic → NOT.

  2. Add four NOT gates (one for each input).

  3. Connect each input (A, B, C, D) to its NOT gate to generate A′, B′, C′, D′.

Now we have both the original inputs (A, B, C, D) and their complements (A′, B′, C′, D′).


Step 5: Implementing the Boolean Expression with AND Gates

Our Boolean expression has multiple product terms connected by AND gates.

Example: A′B′C′D′ means all four inputs are inverted and connected to a 4-input AND gate.

Steps:

  1. Place a 4-input AND gate (Place Component → Logic → AND → 4-input).

  2. Connect the required variables (for example, A′, B′, C′, D′) to that AND gate.

Repeat this process for each product term in the expression.
Since we have eight product terms, we’ll need seven to eight AND gates.


Step 6: Combining Outputs with OR Gates

The dot (·) in Boolean expressions means AND, while the plus (+) means OR.
After generating all the product terms using AND gates, we now combine them with OR gates.

Steps:

  1. Place OR gates (2-input, 3-input, or 4-input).

  2. Group the outputs of the AND gates into the OR gates.

  3. Finally, combine everything into a single output.

This final output represents the full Boolean function.


Step 7: Connecting the Output LED

To visualize the result:

  1. Place an LED at the final OR gate’s output.

  2. Connect it to ground as before.

Now the LED will light up depending on whether the Boolean expression evaluates to 1 (True) or 0 (False) for the given switch inputs.


Step 8: Testing the Circuit with the Truth Table

Run the simulation and toggle the switches (A, B, C, D):

  • 0000 → Output = 1 (LED ON)

  • 0001 → Output = 0 (LED OFF)

  • 0010 → Output = 1 (LED ON)

  • 0011 → Output = 1 (LED ON)

  • 0100 → Output = 0 (LED OFF)

  • 0101 → Output = 1 (LED ON)

  • 0110 → Output = 1 (LED ON)

  • 0111 → Output = 1 (LED ON)

  • 1000 → Output = 1 (LED ON)

  • 1001 → Output = 1 (LED ON)

… and so on, until all input combinations are tested.
As you can see, the circuit behaves exactly as expected according to the Boolean truth table.


Step 9: What’s Next?

In this episode, we focused on implementing a Boolean expression with basic logic gates.

In the next video, we’ll:

  • Build the Boolean expressions for outputs B and C.

  • Extend the design to cover multiple outputs.

  • Eventually, combine all outputs into a 7-segment display circuit.


Final Notes

This project is a great way to visualize how Boolean algebra translates into real logic circuits. Using Multisim makes the process interactive and easy to test.

👉 I’ll upload the Multisim project file so you can download it, modify it, and try it yourself.

Stay tuned for the next episode, where we continue building more outputs and move closer to a complete digital circuit system!