Liquid Crystal Displays or more commonly known as LCDs are one of the most common electronic components which help us interact with an equipment or a device. Most personal portable equipment and even gigantic industrial equipment utilize a custom segment display to display data. For many portable consumer electronics, a segment LCD display is one of the biggest contributors to the overall cost of the device, hence designing a custom segment display can drive the cost down while also utilizing the display area in the most optimum manner. These displays have the lowest cost per piece, low power requirements, and a low tooling fee too.
At first thought, designing a custom segment LCD might look like a Herculean task, but trust me that it is easier than it seems. In this article, we have summarised and compared the display types and available technologies which are required to construct a custom segment LCD. We have also provided a flowchart that can act as a step-by-step guide while you design your own custom LCD. We have also provided the process we followed, a require gathering sheet we used for communicating our needs to the manufacturer, and a few other data and the quotation we received from the manufacturer.
Before we dive deep in, you should know about the common design terminologies associated with segment displays and what they mean.
Segments – It is the smallest unit that can be individually controlled, it can either be in the shape of a bar, dot, or icon.
Common Line – Electrical connection terminal connected to multiple segments
Segment Line – Electrical connection terminal which is connected to only one segment.
Icons: A silhouette of any shape can be placed on the glass which enhances the ability to display data. For example, a symbol of a heart can be made to denote heart rate or an icon for a low battery to show that the battery needs to be charged. Icons are counted as a single pixel or segment and can give a lot more details than similar-sized text.
LCD Duty Cycle – It denotes the time in which the segment is energized, it is given by the on-time by total time per frame.
LCD Bias – It denotes the number of different voltage levels used in driving the segments, static drives (explained later in this article) only have 2 voltage levels or 2 bias voltage while multiplex drives have multiple voltage levels. For example, 1/3 will have 4 bias voltages.
LCDs utilizes the light modulating properties of liquid crystals which can be observed by using polarizing filters. Polarizing filters are special materials that have their molecules aligned in the same direction. If the light waves passing through polarisers have the same orientation as the filter, then the molecules of lights are absorbed by the filter, hence reducing the intensity of light passing through it, making it visible.
In Layman’s language, when an electric current is applied to the electrodes, i.e. to the segment line and common line, it twists the Liquid Crystals w.r.t to the polarizing filter, obstructing the light in that particular area as shown in the figure below. Hence, that area becomes darker and prominent.
A custom LCD is important for maximizing the efficiency of the display area by adding custom symbols and characters. It also helps in reducing the cost and improving energy efficiency of the product. A higher number of custom symbols and specified placement of numerical and alphanumerical characters make the display more informative and readable for the user. This makes it look better than the plain old boring displays we get in the market. Furthermore, we can specify the viewing angle, contrast, and other specifications which can increase durability or give a better value for money for our intended usage. A typical Custom Segment display is shown below, we will also show you how to design and fabricate the same further in the article.
The LCD display doesn’t emit any light of its own, therefore it requires an external source of illumination or reflector to be readable in dark environments.
While designing a custom segment LCD display, we have the leverage of choosing a lot of parameters that affect the final product. From the color of the display to the illumination technique and color of illumination as well as the type of input pins. Some important considerations we need to take while designing a custom 7 segment display are - the type of display, i.e. positive or negative, illumination method, driving technique, polarising type, and connection method. All these design criteria are explained below:
Positive and Negative Displays:
Positive and negative displays can be easily distinguished by the colour of the background and characters. Some common differences between the positive and negative displays are:
Positive Display
Negative Display
Dark image on light background
Light image on Dark Background
Front and rear polarizers are perpendicular to each other
Front and rear polarizers are aligned to each other
Used in areas with high ambient light, the backlight can also be used.
Used in areas with low ambient light, hence the backlights are often used.
Background can be of multiple colours
Pixels can be of multiple colours
Can be used in any display technique
Only possible with transmissive display
So, which one should you choose? When the displays are to be used in areas with higher ambient light, we should select positive segment LCD display as it has better visibility than negative segment LCD displays without using a backlight.
Illumination Technique:
As we know that LED displays don’t emit any light, hence to illuminate it and make it visible in a dark environment, we can use different methods of illumination. The most common LCD Illumination methods are compared below:
Brightness
Size
Inverter required
Power consumption
Durability
Life
(in hours)
LED
Medium
Small
No
Low
High
100,000
Incandescent
High
Medium
No
High
Low
10,000
Electroluminescent (EL)
Low
Small
Yes
Low
High
15,000
CCFL
High
Medium
Yes
Medium
60,000
Fibre Optic
Medium
Small
No
High
High
100,000
For displays that need to be used for budget-friendly devices that should be small and rugged, LED lights are preferred for the displays due to the high durability and low cost of operations. For high brightness, CCFL and Incandescent lights can be used.
LCD Polarizers:
A polarizer film is the most important component of an LCD display, which makes it possible to display characters by controlling the light. There are 3 types of polarizers that can be used in the LCD display, the properties and difference are given below:
Transmissive Polarizer
Reflective Polarizer
Trans-reflective Polarizer
In Transmissive Polarizer, the display is illuminated through backlight, embedded in the display
In Reflective Polarizer, an outside source of light is used for illumination of the display
Transflective Polarizer, can be illuminated through a backlight or the outside ambient lighting
Contrast is better than transreflective polarizer but not as good as reflective polarizer
It has the highest contrast ratio
Contrast is not as sharp as the reflective polarizer
Without a backlight it is difficult to be read
Backlighting is not possible due to an opaque reflector
It can be used with or without a backlight
Consumes highest energy
Consumes lowest energy
Consumes low energy when backlight is turned off.
If your products need to be used with a switchable backlight, then trans-reflective reflectors are best to be used for front reflectors. If the device has to be used without backlight, then we can select a reflective polarizer for the back-panel as it gives the best contrast ratio.
Passive and Active LCD Displays:
Displays can be categorized into two types, passive displays, and active display, passive displays are simpler to construct as they have 2 connections at each segment, the conductors comprise of an Indium Tin Oxide to create an image, whereas the active displays use thin-film transistors (TFT) arranged in a grid. The name is due to its ability to control each pixel individually.
Passive Display
Active Display
Twisted Nematic (TN)
STN
FSTN
Film Super-twisted nematic
TFT Display
Cost
Low
medium
High
Very High
Viewing angle
Low
Medium
High
Very High
Contrast sharpness
Low
Medium
High
Very High
Power Consumption
Low
Medium
High
High
Operation temperature range
-10 to 60 C
0 to 50 C
0 to 50 C
If we need to display a fixed set of data, then we can select a passive display as it is cost-effective and energy-efficient.
Custom Segment LCD - Drive Methods:
It dictates how each segment is connected within the display. There are 2 drive methods, static drive, and Multiplex drive.
Static Drive
Multiplex Drive
Segment pins
Individual pins for all segments
Multiple segments can have the same pins
Common pin
Only one common pin in the LCD
Multiple common pins
Complexity of operation
Easier to operate
Complex to operate
Most optimum application
Optimum for LCDs with few segments
Optimum for LCDs with a large number of segments
Operating voltage
Single operating voltage
Multiple operating voltages
Contrast Ratio
Better contrast ratio than multiplex drive
Lower contrast ratio than the static drive
If your displays have fewer segments, then static LCD drive is preferred as it is easier to control and cheaper to construct, and has a better contrast ratio. But let’s say that if the number of segments in the display are more than 30-40 then a multiplex LCD drive should be preferred as it has multiple common pins, hence reducing the total number of pins required to drive the display.
LCD Interconnection:
LCD interconnections are used for connecting the devices with the LCD screen. They are mainly of 3 types that are:
Elastomer connection or Zebra strip
Minimum contact patch
0.5mm
Pins
Minimum contact patch
1.5mm
Flat Flex Cable
Minimum contact patch
0.28mm
Choosing a connector type!!! For the prototyping phase or if you need to connect your LCD display on a Microcontroller directly, a pin type connector is the best and most economical option you have. If you need to connect your LCD display in a final product with a high volume of production which also requires to be extremely durable, but at the same time should not take up a lot of space, a Flex type LCD Connector will work best for you
Viewing Angle Direction in LCD Displays:
LCDs have limited viewing angles and when seen from an angle they lose contrast and are difficult to be observed. The viewing angle is defined by the angles perpendicular to the center of the display towards its right, left, up, and down which are denoted by the notations 3:00, 9:00, 12:00, and 6:00 respectively. The viewing angle of LCD can be defined as the angle w.r.t. to the bias angle at which the contrast of segments is legible.
To improve the viewing angle in an LCD, a Bias is incorporated in the design which shifts the nominal viewing angle with an offset. Another technique is to increase the Voltage, it affects the bias angle, making the display crisper when viewed from a direction.
For example, the viewing angle of a TN type TFT LCD is 45-65 degrees. Extra-wide polarising film (EWP) can increase the viewing angle by 10 degrees, using an O film polariser can make the viewing angles 75 degrees but these come at a cost of reduced contrast.
LCD Glare filter:
Anti-glare filters are bonded with the top polarising filters using adhesive. It improves the viewability by re-directing light waves so they don’t reflect back towards the viewer thus reducing glare. Newer materials are capable of reducing the front glare by up to less than 0.3%.
Control chip placement:
LCD Control chip or LCD driver chips can be mounted on the flex cable, display, or externally on a PCB. The placement of LCD control chip can affect the cost and size of the display. The 2 most common methods of chip placement are-Chip of Board (COB)and Chip on Glass(COG) which are described below:
Chip on board or surface mounted device
Chip on glass
COG can be used as it is cheaper and makes the assembly process simpler, but if the dimensions are a constraint, then the COB is also a viable option.
We planned to design an air quality monitoring system for which we needed a custom segment LCD panel for an air quality monitoring device. Our product needs to display the following data: 2.5-micron and 10-micron particulate matter (PM) suspended in the air; the units should be in parts per million (PPM). CO2 in the air in PPM along with total volatile organic compounds present in the air in parts per billion (PPB). To make the product more usable, we included time in 24-hour format, Temperature in ºC, Battery status, loudspeaker status, Bluetooth status, and Wi-Fi status. And for some personal touch, we also added how good the air quality in the room is by using 3 different smileys.
We realized that it was impossible to provide all these data in a generic LCD available in the market, thus decided to build a custom LCD for our project.
Steps of designing a custom LCD:
A step-by-step flowchart is shown below to walk you through each and every step of selecting components and getting your custom segment LCD manufactured.
We started by listing down our requirements and drew a mock-up of the display on paper. After finalizing the placement of all the segments and icons on the prototype sketch of the display, we then decided which all icons and segments have to be kept on for the whole time and which needs to be driven. Realizing that there are too many segments, characters and icons, hence we selected a multiplex drive with 8 common pins which helped us bring down the total pins from an estimated 180 pins to less than 40 pins.
Since the device was meant to be used inside houses and offices, which are more often than not well lit and protected from environmental conditions, we opted for a positive mode display. For superior contrast ratio and better viewing angle, we chose a Film Super Twisted Nematic Display (FSTN) with a drive condition of 1/8 Duty and bias of 1/4.
Usually, the displays are mounted at a height of 4.5 feet from the ground, thus the viewing direction was selected to be 12'O clock with an operating frequency of 64Hz. We selected a Transmissive polarizer for the front glass and a reflective polarizer for the rear glass so that the natural light can pass through the front panel and the display can achieve the maximum contrast without the need for backlighting and we opted for the pin type connectors as they are easy for prototyping and are suitable for harsh environment with a lot of vibrations and shocks which best suited our purpose.
In the above image of a custom display design, we sent to the manufacturer, the red lines over multiple characters indicate that all these are considered as a single segment. For the sake of simplicity, we added test like T, S, U, B to denote Text, Symbols, Units, and Battery respectively. These characters were followed by numbers to simplify communication between us and the manufacturer. For example, if we needed any particular text or symbol to remain on, we can easily specify that to the manufacturer by using the corresponding text for that segment.
We mailed our requirements to multiple LCD manufacturers, (you will find a lot of LCD manufacturers on the Internet). Most LCD manufacturers have competitive pricing, and reply within a week. A sample requirement sheet is shown above which a customer needs to fill to specify all the details to the manufacturer.
This is a sample Custom Segment LCD quotation we got from one of the manufacturers. As you can see, the cost is based on the quantity. Higher the quantity, lower the cost. Apart from the cost per quantity, there is one more component called tooling fees. Tooling fee is a one-time fee charged by the manufacturer. It is for the technical design, support, and customization of the product. Customization of PCB or tooling of LCD can drive the tooling price higher or lower.
The tooling time and cost depend on how detailed and accurate designs you sent to the manufacturer. They then send the exact dimensions and technical details of the product they will be manufacturing. Once you confirm the design, they manufacture and ship the product which might take 4-8 weeks to arrive depending on the size of the order and mode of transportation selected.
Conclusion:
A custom segment LCD can help you personalize your product while also saving the overall cost of your product. The whole process will take you around 2-3 months, which will include the designing phase, prototyping phase, and getting your custom segment LCDs delivered to your doorstep. Higher ordering quantity will reduce the cost per piece of each unit, thus driving down the cost of your final product.
In the digital age, LCD screens have become an integral part of our daily lives, from smartphones and laptops to televisions and digital signage. But have you ever wondered how these screens work to deliver crisp images and vibrant colors? As an expert in display technology, I will guide you through the fascinating world of LCD screens, unraveling the complex processes that make these devices so essential in our modern world.
We’ll delve into the fundamental components that constitute an LCD screen and explore the pivotal role that liquid crystals play in this technology. We’ll also shed light on the intricate process of backlighting, which is crucial for the visibility of images on the screen.
Further, we’ll break down the science behind pixel formation in LCD displays, a process that is key to the clarity and sharpness of the images we see. We’ll also discuss the function of color filters, which are responsible for the rich and varied hues we enjoy on these screens.
Finally, we’ll navigate through the diverse types of LCD screens available in the market today, understanding their unique features and applications.
This comprehensive guide aims to address common misconceptions and alleviate any apprehensions you may have about LCD technology. So, whether you’re a tech enthusiast eager to expand your knowledge or simply curious about the technology you use every day, this article is sure to enlighten and inform. Let’s embark on this journey to understand the inner workings of LCD screens.
1. The Basic Components of an LCD ScreenAt the heart of every LCD screen, there are three primary components that work together to create the images we see. Firstly, the backlight provides the light source necessary for the display. Secondly, the liquid crystal layer, which is sandwiched between two polarizing filters, manipulates the light from the backlight to create images. Lastly, the color filters add the necessary colors to the images.
Delving into the core of LCD technology, we find the fascinating world of liquid crystals. These unique substances, which exhibit properties of both liquids and solid crystals, are the key players in LCD screens. They have the fluidity of a liquid, but their molecules are arranged in a crystal-like way. This dual nature is what makes them perfect for display technology.
When an electric current is applied to these liquid crystals, their molecular structure changes. This change in structure alters the way light interacts with them. By controlling the current, we can control the amount of light that passes through the liquid crystals, effectively creating different shades of colors. This is how images are formed on an LCD screen.
Tip: To extend the life of your LCD screen, avoid exposing it to extreme temperatures. Liquid crystals are sensitive to heat and cold, and extreme temperatures can cause them to malfunction. Also, remember to clean your screen with a soft, dry cloth to prevent scratches and damage to the liquid crystals.
3. Understanding the Backlighting Process in LCD ScreensOne of the most crucial components of an LCD screen is the backlighting process. This process is responsible for illuminating the pixels on the screen, making the images visible to the viewer. The backlighting process begins when the light from a series of fluorescent or LED lamps is diffused across the screen by a panel known as the diffuser. This diffused light then passes through a series of polarizing filters and a liquid crystal layer, which manipulates the light to create the images we see.
There are several key steps in the backlighting process that are critical to the functioning of an LCD screen. These include the generation of light, the diffusion of light, the manipulation of light by the liquid crystal layer, and the final polarization of light. Each of these steps is crucial in ensuring that the images displayed on the screen are clear, bright, and accurately colored. Understanding these steps can help users better appreciate the complex technology behind their everyday devices.
4. How Pixel Formation Occurs in LCD DisplaysPixel formation in LCD displays is a fascinating process that involves a complex interplay of light, color, and electricity. Each pixel on an LCD screen is composed of three sub-pixels: red, green, and blue. These sub-pixels are controlled by a matrix of thin-film transistors (TFTs) that switch on and off to allow varying amounts of light to pass through.
When an electric current is applied to the liquid crystal layer, the crystals align in a way that either blocks or allows light to pass through. The degree to which the crystals twist is determined by the voltage applied, which in turn determines the amount of light that reaches each sub-pixel. By controlling the light reaching each red, green, and blue sub-pixel, the LCD display can produce a full spectrum of colors.
In conclusion, the formation of pixels in an LCD display is a result of a carefully orchestrated dance of light and electricity. It’s the precise control of this process that allows LCD displays to produce sharp, vibrant images. Understanding this process not only gives us a greater appreciation for the technology, but also helps us make more informed decisions when purchasing or troubleshooting LCD displays.
5. The Function of Color Filters in LCD TechnologyColor filters play a crucial role in LCD technology. These filters are responsible for the vibrant display of colors that we see on our screens. Each pixel on an LCD screen is divided into three subpixels, each with a dedicated color filter – red, green, and blue. These subpixels, when combined, can produce a wide spectrum of colors. The intensity of light passing through these filters is controlled by the liquid crystals, which in turn determines the color that is displayed.
Let’s delve deeper into the process. The backlight of the LCD screen emits white light, which passes through the polarizing filter. This light is then directed towards the subpixels. The liquid crystals control the amount of light that can pass through each subpixel. The combination of light intensities from the red, green, and blue subpixels results in the final color that we see on the screen.
Here is a simplified sequence of how color filters work in LCD technology:
When it comes to LCD screens, there is a wide array of types that cater to different needs and applications. Twisted Nematic (TN), In-Plane Switching (IPS), and Vertical Alignment (VA) are among the most common types of LCD screens. Each of these types has its unique characteristics and advantages.
Understanding the different types of LCD screens is crucial when choosing a display for a specific application. For instance, a graphic designer might opt for an IPS screen for its color accuracy, while a gamer might prefer a TN screen for its fast response time. Meanwhile, a user who wants a balance between color accuracy and response time might find a VA screen to be the most suitable option.
Moreover, these different types of LCD screens also find their uses in various devices and industries. TN screens are commonly used in gaming monitors and some televisions. IPS screens are often found in high-end monitors, smartphones, and tablets due to their superior color reproduction and viewing angles. VA screens, meanwhile, are typically used in televisions and monitors where a balance between performance and image quality is required.
Frequently Asked Questions What is the role of polarizing filters in an LCD screen?Polarizing filters in an LCD screen are crucial for controlling the light that passes through the liquid crystals. They are oriented at 90 degrees to each other, allowing only certain orientations of light to pass through. When the liquid crystals twist, they change the light’s orientation to match the second filter, allowing it to pass through.
Why is backlighting necessary in LCD screens?Backlighting is necessary in LCD screens because liquid crystals do not emit light on their own. The backlight illuminates the liquid crystals from behind, making the images visible to the viewer. Without the backlight, the screen would be very dim and hard to see.
How does an LCD screen produce different colors?An LCD screen produces different colors using color filters and varying the intensity of the backlight. Each pixel on an LCD screen is made up of sub-pixels that are red, green, and blue. By varying the intensity of light that passes through these sub-pixels, an LCD screen can produce a full spectrum of colors.
What are the advantages of LCD technology over other display technologies?LCD technology has several advantages over other display technologies. It consumes less power, making it ideal for portable devices like laptops and smartphones. LCD screens also have no risk of burn-in, unlike plasma screens. They also have excellent color accuracy and can be made very thin and light.
What are the different types of LCD screens?There are several different types of LCD screens, including Twisted Nematic (TN), In-Plane Switching (IPS), and Vertical Alignment (VA). TN screens are the most common and are known for their fast response times. IPS screens have better color accuracy and wider viewing angles, while VA screens offer better contrast and deeper blacks.