LCD Display: Working Principle & Simple Science Kit Projects for Beginners

Table of Content

• What is LCD? Full Form and Working Principle
  
• How an LCD screen actually works
  
• The Layers Inside an LCD Panel
  
• Types of LCD technology
• Connecting the Arduino LCD display together
• So why do we love LCDs so much in science kits and the STEM world in general?
• Conclusion
• FAQs

We all spend the majority of our day looking at screens; whether it is a mobile phone, laptop, a television screen, a display on the microwave, or on a cash machine at the ATM; however do you know what is actually going on beneath the surface of that thin panel, which is so capable of creating those incredibly sharp images and letters? Almost none of us do, and yet this gap in knowledge can lead to serious trouble when we are assembling a component Arduino lcd display, creating an electronics science kit, or teaching a STEM kit lesson; the question of the 'how' will inevitably arise.

In this blog, we will bring light to the actual makeup of an LCD. We will explore the complete word for LCD and the layers it actually contains, as well as find out what is happening with the liquid crystal and how switching on those pixels affects them, and what all of this actually means when considering school science lessons and projects involving microcontrollers. After you have finished reading this blog, you will know exactly what an LCD display is made up of.

What is LCD? Full Form and Working Principle

LCD means Liquid Crystal Display. That's the LCD full form, which basically means something important to know: that display relies on something that behaves as both solid and liquid at the same time.

●     It's not a new invention; the first discovery that led to the creation of LCD came in 1888, and it was discovered by Austrian botanist Friedrich Reinitzer. He noted that certain substances have two distinct melting points and at a given range of temperatures can show two distinct optical characters, thus it has properties of fluid and solid simultaneously. This was the origin of today's LCD screens used on billions of products.

●     The working is rather easy to explain; unlike LEDs, they do not produce light, LCDs just allow the light to pass through them, like literally thousands of window blinds. If they are opened, then the light passes through, while if closed, it is not allowed to. The lcd screen consists of millions of tiny window blinds arranged in a matrix.

How an LCD screen actually works

LCDs work on a simple principle: light passing through liquid crystals twists them. That's precisely what happens in each section of an LCD screen:

Light enters the screen, already polarized

Initially, natural light vibrates in every direction. A polariser filter at one end of the screen only lets through horizontal vibrations. The horizontally vibrating light is then aimed at the liquid crystals.

The liquid crystals twist the light

If a zero voltage is applied, the crystals are organized so that they twist the horizontally vibrating light 90 degrees so that it is vertically vibrating.

A second polariser filters the light

At the opposite side of the screen is another polariser. This is polarized 90 degrees relative to the first one. If the liquid crystals twist the light, the light can pass through the second polariser, and the pixel is therefore bright. If a voltage is applied to the liquid crystals, the crystals are untwisted, and the horizontally vibrating light is blocked by the second polariser, and the pixel is therefore dark. Understanding this on/off behavior at the pixel level is what separates someone who uses screens from someone who truly understands electronics.

The image is produced by color filters

In an LCD screen with colors, each pixel is split into 3 parts with one of each of the color filters: red, green, and blue. A particular amount of each color light can be allowed through the liquid crystal in each of these 3 parts and thus a colored pixel. A whole color picture can be produced from a million RGB pixels.

The Layers Inside an LCD Panel

An explanation of the different layers within an LCD screen. It is useful to know what each layer does, and it makes much more sense if you examine the panel's construction in its entirety. LCD panels are essentially "layer cakes".

●     Backlight layer - Generally, lcd panels do not produce their own light and are backlight layers – commonly of LED light - inserted behind the panel to evenly light up the layer in front of it.

●     Rear polarizer - The first filter that has the purpose of only allowing light to pass that has already been polarized (vibrated) in a single dimension.

●     TFT glass substrate - Circuits called Thin Film Transistors or TFT's are put onto this glass substrate; they have the responsibility of controlling how much voltage is applied to each individual sub-pixel.

●     Liquid crystal layer - This is where all the clever bits of it are! The liquid crystal molecules lie in between two layers of glass, where their direction can be controlled using an electric field.

●     Color filter glass - On this layer, there are R, G, and B filters in alignment with the individual sub-pixels.

●     Front polarizer - The final filter in the system of layers. If the light has not been rotated correctly, it is absorbed by this layer.

Each layer has to integrate carefully so that the whole system operates appropriately; if any of the layers were to become misplaced, it would affect the appearance of the panel, leading to errors or artifacts on the display module.

Types of LCD technology

Not all types of lcd panels function in precisely the same way. There are different ways to construct the modules to make them more suitable for various tasks.

TN (Twisted Nematic) panels

These are the oldest type of LCD panel. As mentioned in the discussion, the principle of operation involves twisted nematic liquid crystals, which can either be left 'twisted' or relaxed by applying a voltage, which allows the liquid to align and be polarized by both filters. Its primary benefit is speed of switching, while the major downside is poor viewing angles and color.

IPS (In-Plane Switching) panels

IPS operates on a slightly different principle in that the liquid crystals are arranged horizontally. This means that rather than twisting within the material, they rotate in parallel lines. The main benefit is extremely good viewing angles and color performance, and now most smartphone displays and high-end monitors use IPS technology.

VA (Vertical Alignment) panels

In their native state, these panels have liquid crystals that are arranged vertically. The benefit of this is extremely high contrast ratios and black levels, although this does compromise the viewing angle to a certain extent when compared with IPS displays, and possibly has higher response times.

Connecting the Arduino LCD display together

One of the most widespread methods that learners and makers will find for accessing and utilizing lcd working principle technology is through an Arduino LCD display project. It's only natural to connect Arduino with the 16x2 LCD display modules, given Arduino's open source and multi-platform microcontroller ideology.

Components of a very simple Arduino LCD display requires and general setup involving:

●     Connecting the LCD module to the Arduino: connecting the module requires 6 digital pins, and they are used when communicating in 4-bit mode. The 8-bit mode requires 10; the more beginner-friendly 4-bit mode is generally preferred.

●     The Liquid Crystal Library: this library is shipped with Arduino's IDE, and allows all interaction between the Arduino and the HD44780 controller; the only thing to do to print to the display is a simple write operation.

●     The education received: the Arduino lcd display will allow the student to learn about parallel communication, how libraries provide easy interfaces to complex interactions with hardware, as well as learn about brightness and contrast.

Just imagine a student hooking a temperature sensor up to the Arduino. This microcontroller uses the analog reading from the sensor to convert the reading into degree's C and output "Temp: 27C" to the LCD. This one project will cover analog inputs, conversion of values, serial communication, and output to a display. I think it's one of the most useful experiments to try at school.

So why do we love LCDs so much in science kits and the STEM world in general?

It is one of the most popular parts that you will find in any well- stocked electronics science kit, indeed any STEM activity kit at all! Here's why:

●     Responsiveness: A student can type a message, then press send, and have the text display instantly on the screen. A very powerful tool when it comes to education!

●     Multiconcept Learning: There is simultaneous teaching of electricity, optics, programming, and engineering design, all contained in one lcd project.

●     Cost efficiency: LCDs provide tremendous educational impact for the cost of the module.

●     Curving: There is so much learning to do, starting with the basic "hello world" and continuing on to fully programmed menu-driven systems, display of sensor inputs, and custom characters, among other things.

It has been noted by schools using STEM kits with the addition of LCD modules that students seem more engaged in the electrical portion of the science curriculum. It helps students grasp concepts of programming when code is translated to a visible outcome on a screen.

Conclusion

We use the implementation of LCD technology in nearly all aspects of our everyday lives, from a 16x2 LCD display screen in your pocket (i.e. A mobile phone) right the way through to a device controller screen on the part of machinery. If you learn about the core construction of an LCD display screen – that it is made up of a layer of liquid crystal, a back-light, and color filters, and so on- then that can be applied to any LCD display module you see on an Arduino LCD display project, a STEM activity pack, or a large electronic science kit. An LCD working principle is simple when it is broken down into segments, and knowledge from this will go a long way when you want to get your head around electronics.

A student, teacher, or indeed anybody who wants to: please go out and purchase a finished school science project from one of the many out there, get a 16x2 LCD display module, plug it into an Arduino, and upload some code. A school science project of that nature will take you further in understanding how a display works than one would from reading in a textbook. The lcd is one of the best examples of how an electronic component works perfectly when bridging the gap between theory and practice, and after you've had an LCD display screen working on your desk, you will always understand how screen displays are energized.

FAQs

Q1. What is the abbreviation LCD?

LCD is short for Liquid Crystal Display. Liquid crystal is simply the name used to describe a medium which will allow a display to control a light source.

Q2. How is LCD different to LED?

An LED display produces its own light source, but the LCD display needs an external light source to be controlled by the liquid crystals. Because of this an external light source of LEDs is often added to the rear of an LCD screen to illuminate it.

Q3. Can I use a LCD on any Arduino board?

You can use the standard 16x2 LCD on almost any of the existing Arduino boards that you can get ahold of (Uno, Mega, Nano etc.). If you have included the LiquidCrystal library, it should work on any board you try!

Q4. My LCD display shows squares instead of characters. What did I do wrong?

Nearly always, it is the contrast. Try just winding the little pot that is connected to V0 around until the characters can be displayed.

Q5. Are LCD's any good for science experiments at school?

Yes, these displays are quite cheap to purchase, are not to difficult to wire up and are extremely readable. They are possibly one of the best electronic components to get hold of for any science experiment.