A Very Short Introduction to Digital Electronics

Depending on how you look at it, the Digital Revolution sort of starts with Logic Gates

Logic gates are the fundamental building blocks of digital electronics. A single logic gate has a simple function,  but, when you connect them together you can build circuits which can do much, much, more. Put enough of them together and you can make a calculator. More still, and you get computers, ipads, and iphones. When you connect cellphones and computers, you get the Internet, Facebook, and the whole modern world we live in.

Cartoon of Toaster texting ‘UR toast is ready’

Woa there! Not so fast. Lets back up a little.

What is Digital?

In Digital Electronics, the voltage on the wires or signals can be one of two values:

  • zero volts (or more commonly known as 0)
  • power supply voltage (or more known commonly as 1)

The 0 value is also known as OFF, LOW, L,  GND, 0v, -ve., and the 1 value is also known as  ON, HIGH, H, +ve.

In the digital world the signals are either 1s or 0s.

Computers have only two fingers.

Most people count numbers using the decimal system, or base 10. That’s because we humans have ten fingers. But, in a digital circuit there is only a 1 and a 0. By using just two values, circuits do all their counting using base 2 or the binary system.

When we humans need to write down a number bigger than 10 we use extra digits for the tens and hundreds. Likewise, in digital circuits extra signals are used to represent each of the different binary digits.

That’s why a computer only has two fingers!

Cartoon of computer with two cartoon pointy finger hands pointing upwards

What is a logic gate?

A logic gate is an electronic circuit that performs simple operations on digital signals. The basic gates are:

  NOT – this gate inputs a signal and outputs another signal with the opposite value, it changes a 1 to a 0, or a 0 to a 1.

  AND – this gate inputs two signals (lets call them A and B) and outputs a 1 only if input A ‘AND’ input B are both 1‘s

  OR – this gate inputs two signals (A and B) and outputs a 1 if input A ‘OR’ input B are 1

  EXCLUSIVE-OR – this gate inputs two signals (A and B) and outputs a 1 if A ‘OR’ B are different from each other

Each gate has a distinctive symbol, which are commonly used in schematic circuit drawings.

There are more gates than are shown here but they can all be made up by combining these ones in different ways.

 

What makes Logic Gates so special?

With the help of Logic Gates, signals can be combined to do some very useful operations like:

  • add or subtract two numbers
  • compare two numbers
  • remember a number to be used later (in other words, a memory)
  • route a number from one circuit to another

These operations form the basis of all the digital products in the world today. When you connect them together you can start to make calculators, computers, and microcontrollers (like the MSP430)

And basically that is Digital Electronics in a nutshell!

Obviously there is much, much more to this but this is good enough to get you started.