Everything you need to know about designing a Segment LCD

Apr 13, 2021 | Articles

Everything you need to know about designing a Segment LCD

Outline

  • Common Terminology used in Segment LCD Displays
  • How Segment LCDs Work?
  • Why do you need a Custom LCD Display?
  • Illumination Technique:
  • Passive and Active LCD Displays:
  • Custom Segment LCD – Drive Methods:
  • LCD Interconnection:
  • LCD Glare Filter
  • Control Chip Placement
  • Conclusion

 

Are you curious to know about the production process of Segment LCD?

Liquid Crystal Displays, more commonly known as LCDs, are among the most common electronic components that help us interact with a piece of device or equipment.
A segment LCD is one of the most significant contributors to the overall cost of the device for many portable consumer electronics. Hence designing a custom segment LCD can drive the price down. These segment LCDs have
Low cost per piece
Low power requirements,
Low tooling fee.
Designing a custom segment LCD is not difficult. This article summarises and compares the display types and available technologies required to construct a custom segment LCD. We have provided the process we followed.

1. Common Terminology used in Segment LCD Displays

Common Terminology used in Segment LCD Displays

You should know about the standard design terminologies connected with segment displays and what they mean.

  • Segments

The smallest unit that an individual can control can be in the shape of a bar, dot, or icon.

  • Common Line

Common lines are electrical connection terminals connected to multiple segments.

  • Segment Line

Segment lines are electrical connection terminals which are connected to only one segment.

  • Icons

A silhouette of any shape placed on the glass, enhancing displaying data. For example, an icon for a low battery indicates that the battery needs to be charged, or a heart symbol indicates heart rate. Icons are counted as a single segment and give more details than similar-sized text.

  • LCD Duty Cycle

It indicates the time in which the segment is energized, and the on-time gives it by total time per frame.

  • LCD Bias 

It indicates the number of different voltage levels used in driving the segments; for example, static drives only have two voltage levels. In contrast, multiplex drives have multiple voltage levels. 

2. How do Segment LCDs Work?

How do Segment LCDs Work?

The light modulating properties of liquid crystals utilized by LCDs, observed by using polarizing filters, are unique materials with their molecules aligned in the same direction. 

In Layman’s language, when electric power is applied to the electrodes, i.e., to the common line and segment line, it twists the Liquid Crystals for the polarizing filter, blocking the light in that particular area.

3. Why do you need a Custom LCD Display?

Why do you need a Custom LCD Display?

A custom LCD is necessary for maximizing the efficiency of the display area by adding custom characters and symbols. It helps improve the energy efficiency of the product and reduces the cost. Specified placement of numeric and alphanumeric characters and more custom symbols makes the display more readable and informative and looks better than the plain old boring displays. 

Moreover, we can specify the viewing angle, contrast, and other specifications, which gives a better value for money for our expected usage.  

The LCD doesn’t emit any light; therefore, it requires an external illumination source or backlight.

Positive Display

  • It shows the dark image on a light background.
  • It has front and rear polarizers and is perpendicular to each other.
  • It is used in areas with high ambient light, and the backlight can be used.
  • Its background can be of multiple colors.
  • It can be used in any display technique.

Negative Display

  • It shows a light image on a dark background.
  • Its front and rear polarizers are aligned to each other.
  • It is used in areas with low ambient light, and the backlights are often used.
  • Its pixels can be of numerous colors.
  • It is only possible with a transmissive display.

 

Which one should you choose?

When the displays are used with higher ambient light, select positive segment LCD as it has better visibility than negative segment LCDs without a backlight.

4. Illumination Technique

Illumination Technique

As we know, an LCD doesn’t emit any light, but we can use different brilliance methods to lighten it and make it visible in a dark environment. The most common LCD Illumination methods are the following:

  • Transmissive Polarizer
  • In Transmissive Polarizer, the display is lighted through a backlight inserted in the display.
  • Its contrast is better than a transflective polarizer but not better than a reflective polarizer.
  • It is without a backlight, and it is not easy to read.
  • It consumes the highest energy.
  • Reflective Polarizer
  • An external source of light is used for the brilliance of the display in Reflective Polarizer.
  • It has the highest contrast ratio.
  • Due to an opaque reflector, there is no need for a backlight.
  • It consumes the lowest energy.
  • Trans-reflective Polarizer
  • Transflective Polarizer can be lightened through a backlight or the outside ambient lighting.
  • Its contrast is not sharp as a reflective polarizer.
  • It can easily be used with or without a backlight.
  • When the backlight is turned off, it consumes low power.

 

Trans-reflective reflectors are best used for front reflectors if your product needs a switchable backlight. 

We select a reflective polarizer for the back panel as it gives the best contrast ratio if the device is without a backlight.

5. Passive and Active LCD Displays

Passive and Active LCD Displays

LCD displays can be categorized into two types: passive displays and active displays. 

Passive Display

Passive displays are simpler to create as they have two connections at each segment; the conductors comprise an Indium Tin Oxide to create an image. 

  • Twisted Nematic (TN) and STN
  • Low and medium cost
  • The viewing angle is low or medium
  • Contrast sharpness is low
  • Power Consumption is low
  • Operation temperature range is -10 to 60 C or 0 to 50 C

Active Display

The active displays use TFT or thin-film transistors arranged in a grid and control each pixel individually.

  • FSTN Film Super-twisted nematic
  • TFT Display
  • Cost is High or very high
  • The viewing angle is high or very high
  • Contrast sharpness is high
  • Power Consumption is high

6. Custom Segment LCD – Drive Methods

Custom Segment LCD - Drive Methods

Custom Segment LCD Drive indicates how each segment is connected within the display. There are two drive methods, static drive and Multiplex drive.

a. Static Drive

Static Drive

  • Segment pins: 

Individual pins for all segments

  • Common pin:  

one common pin in the LCD only.

  • The complexity of operation: 

Easier to operate.

  • Most optimum application:

 Optimum with few segments for LCDs.

  • Operating Voltage: 

Single operating Voltage

  • Contrast Ratio: 
  • It has a better contrast ratio than a multiplex drive

b. Multiplex Drive

Multiplex Drive

  • Segment pins: 

Multiple segments can have the same pins

  • Common pin: 

Multiple common pins

  • The complexity of operation: 

Complex to operate

  • Most optimum application: 

Optimum for LCDs with a large number of segments

  • Operating Voltage: 

Multiple operating voltages

  • Contrast Ratio: 

Lower contrast ratio than the static drive

A static LCD drive is preferred as it is cheaper to construct, easier to control, and better contrast if your displays have fewer segments. 

You should prefer a multiplex LCD drive if the number of segments in the display is more than 30-40 as it has multiple common pins and reduces the total number of pins needed to drive the display.

7. LCD Interconnection

LCD Interconnection

LCD interconnections are used for connecting the LCD screen with devices. They are 3 types that are following:

a. Elastomer connection or Zebra strip

Elastomer connection or Zebra strip

  • Silicon Strips of alternative insulator and conductor.
  • Fast assembly and disassembly.
  • It is preferable to use in an environment with high vibrations.
  • It yields higher conduction than pins.
  • It requires a specialized compression bezel.
  • The minimum contact patch is 0.5mm

b.Pins 

    Pins

    • These are attached directly to the display.
    • Using pins most accessible to work with during product, production of smaller batches, or prototyping.
    • Provides exceptional protection from a harsh environment with shock and vibrations.
    • Have the minimum number of interconnects per inch.
    • The minimum contact patch is 1.5mm.

    c. Flat Flex Cable 

    Flat Flex Cable

    • LCD and PCB are connected by flex cable using pressure and heat.
    • Offer excellent protection to breakage due to external stress and is suitable for harsh environments
    • A high density of contact points.
    • Not ideal for smaller costs as the initial setup cost is high.
    • Minimum contact patch 0.28mm

     

    A pin-type connector is the best to connect your LCD on a Microcontroller directly and the most economical option you have. 

    A Flex-type LCD Connector will work best for you if you need to connect your LCD in a final product with a high production volume.

    8. Viewing Angle Direction in LCD Displays

    Viewing Angle Direction in LCD Displays

    LCDs have limited viewing angles, and they lose contrast and are difficult to be observed when seen from an angle. The viewing angle is perpendicular to the center of the display towards its right, left, up, and down, denoted by the notations 3:00, 9:00, 12:00, and 6:00, respectively.

    Viewing Angle Direction in LCD Displays

    The viewing angle of an LCD is defined as the angle at which the contrast of segments is legible. A Bias is incorporated in the design to improve the viewing angle in an LCD and with an offset to shift the nominal viewing angle.

    9. Control Chip Placement

    Control Chip Placement

    LCD Control chip or LCD driver chips mounted on display, the flex cable, or externally on a PCB. The placement of an LCD control chip can affect the cost and size of the display. The two most common methods of chip placement are which are described below:

    a. The chip of Board (COB)

    The chip of Board (COB)

    Chip on board or surface mounted device 

    • PCB is mounted behind the glass.
    • It can contain different circuits of the product in addition to the LCD circuitry.
    • Connections have to be designed on display.
    • Higher designing cost 
    • Higher cost due to extra components.
    • Complex assembly process.

    b. Chip on Glass(COG)

    Chip on Glass(COG)

    • It utilizes the LCD glass to have the driver circuit and is reducing the size.
    • The Chip on Glass LCD is connected to other circuits with the LCD as mentioned above connection methods.
    • All connections like a driver and ICs are present on display.
    • Lower designing and parts cost.
    • Simple assembly process.

     

    COG makes the assembly process simpler as it is cheaper. If the dimensions are a constraint, the COB is an applicable option.

    Conclusion

    A custom segment LCD can help you personalize your product and save the overall cost of your product. The whole process will take around 2-3 months, including 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 your final product price, and we manufacture our product for higher or bulk orders.content goes here. Edit or remove this text inline or in the module Content settings. You can also style every aspect of this content in the module Design settings and even apply custom CSS to this text in the module Advanced settings.

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