# Creating Logic Gates using Transistors

As you know, computers can only process binary data which consists of 0’s and 1’s. This is due to the fact that the main processing components (e.g. the CPU) are made of transistors: tiny electronic switches that can be turned on (1) and off (0).

A transistor is an electronic component with three pins. Basically, a transistor is a switch (between two of the pins: the collector and the emitter) that is operated by having a small current in the third pin called the base.

Use the checkboxes below this transistor to understand how applying a voltage to the base of a transistor is equivalent to turning on a switch.

Apply voltage to: Base   –    Collector

A transistor acts like a switch, operated by applying a small current to the base.

Transistors come in many shapes and sizes. Inside the CPU fully integrated nano-transistors are just a few atoms wide!

Using a small breadboard circuit, we can test the behaviour of a transistor. You can reproduce the following circuit see how the transistor operates.

#### Logic Gates

A logic gate is a small electronic circuit made of one or two transistors and used to process binary data. Logic gates such as the AND gate, OR Gate, NOT Gate, XOR gate and NAND gates are the key building blocks of any computer system.

In this challenge, you will recreate some of theses logic gates by combining several transistors together. You will then test your logic gates to record their behaviour using a truth table, that will show all the outputs of your logic gates for all possible input combinations.

Use the tabs below to see how some of the key logic gates are built using transistors:

AND GateOR GATENOT GATENAND GATE

Now let’s recreate this circuit a breadboard and a few electronic components:

Truth Table:

 Input A Input B Output X 0 0 01 0 1 01 1 0 01 1 1 01

Now let’s recreate this circuit a breadboard and a few electronic components:

Truth Table:

 Input A Input B Output X 0 0 01 0 1 01 1 0 01 1 1 01

Now let’s recreate this circuit a breadboard and a few electronic components:

Truth Table:

 Input A Output X 0 01 1 01

Now let’s recreate this circuit a breadboard and a few electronic components:

Truth Table:

 Input A Input B Output X 0 0 01 0 1 01 1 0 01 1 1 01

#### Integrated Circuits?

An integrated circuit (also referred to as a chip, or a microchip) is a set of electronic circuits on one small flat piece (or “chip”) of semiconductor material, normally silicon. The integration of large numbers of tiny transistors into a small chip results in circuits that are smaller, cheaper, and faster than those constructed of discrete electronic components.

Integrated Circuit 7408: Quad 2-input AND gate

More complex integrated circuits include binary adders (half-adder, full adder used to perform binary additions) and flip-flop circuits used to implement volatile memory.

List of 7400 series integrated circuits:
https://en.wikipedia.org/wiki/List_of_7400_series_integrated_circuits

#### Mirco-Processors?

A microprocessor is a computer processor which incorporates the functions of a computer’s central processing unit (CPU) on a single integrated circuit (or at most a few integrated circuits). The microprocessor is a multipurpose, clock driven, register based, digital-integrated circuit which accepts binary data as input, processes it according to instructions stored in its memory, and provides results as output.

A microprocessor is a computer processor which incorporates the functions of a computer’s central processing unit (CPU) on a single integrated circuit

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