Classical Computing – Introduction to Logic Gates

Introduction to logic gates

As computers use 1s and 0s, we need a way to manipulate these values to produce different outcomes. For this, we use logic gates.

Logic gates are the building blocks of digital circuits. These allow our smartphones, computers, and other devices to process data, store memory, and perform arithmetic operations. You are carrying around logic gates every day in your pocket.

Types of logic gates:

1. NOT gate

• It has just one switch.
• If the switch is on, the output is off, and vice versa.
• It basically flips the input: if it's on, it makes it off, and if it's off, it makes it on.

2. AND gate

• Imagine you have two switches, A and B. For the AND gate to be active (outputting a "1" or "true"), both switches must be turned on.
• If either switch is off, the output will be off.

3. OR gate

• Picture two switches, A and B, again. With an OR gate, if either switch A or switch B is turned on, the output is on.
• In other words, as long as at least one switch is on, the output is on.

4. NAND gate

• It's like an AND gate followed by a NOT gate.
• If both switches A and B are on, the output is off. Otherwise, the output is on.

5. NOR gate

• Similar to the OR gate but followed by a NOT gate.
• If either switch A or switch B is on, the output is off. Only when both switches are off, the output is on.

6. XOR gate

• Exclusive OR gate.
• If either switch A or switch B is on, but not both, the output is on.
• If both switches are on or off, the output is off.
• It's like saying "one or the other, but not both."

7. XNOR gate 

• An XNOR gate is a logic gate that produces an output of "true" (or "1") only when both inputs are the same, either both "true" or both "false."
• In other words, it gives a true output when the inputs are either both on or both off.

Teachers can use a classroom presentation to introduce the topic of logic gates. Download the presentation as pptx.

Activity 1: Worksheet about logic gates

Students will complete a worksheet. There are short questions and open-ended research questions. This worksheet is differentiated for two levels (introductory and advanced).

You can download:
 

• Worksheet Logic Gates (introductory level) as docx and pdf
• Answers to Logic Gates (introductory level) as docx and pdf
• Worksheet Logic Gates (advanced level) as docx and pdf
• Answers to Logic Gates (advanced level) as docx and pdf

Activity 2: Logic gate simulator

Discover and play with the logic gate simulator. Try to anticipate the answers and check whether your assumption was right.