A liquid crystal display is a mode of display used in digital equipment replacing many other modes of displays such as cathode ray tube, LED displays and plasma displays. Often abbreviated as LCD, liquid crystal displays are a thin flat panel which is made up of several blocks filled with liquid crystals. LCD works either by allowing the light to pass through it or by blocking it. Liquid crystal displays are widely used nowadays in various electronic equipment such as digital clock, calculators, various home appliances, laboratory equipment etc. LCD displays are ultra thin and consume lesser power compared to any other mode of display.
Liquid crystals are substances which exist in a state between a solid and a liquid. When solids are heated up to a sufficient amount of temperature they assume the state of a liquid crystal which can be termed as a quasi-solid state. As in the case of a solid substance, the liquid crystals maintain their orientation but is capable of moving around in different directions. If we apply a little more heat to the liquid crystal it changes it’s stated to that of a liquid.
Most of the character LCD module used in embedded systems are 16X2 and 20X4 displays. This means that the LCD displays can display two lines with 16 characters each and 4 lines with 20 characters each respectively. There are 14 pins for a character liquid crystal display module.
Construction and working
Each LCD block or pixel is a thin layer of liquid crystal molecules arranged between two polarizing sheets and two electrodes. When electric current generated using the electrodes passes through the liquid crystal, the liquid crystals get aligned and the direction of the alignment is determined by the polarization of the light.
Construction of a liquid crystal display is not a complicated one as an LCD device is nothing but the liquid crystal sandwiched between two polarized glass filters. Take the glass filter without the polarizing film on top of its surface and make minute grooves on top of it by rubbing it with a special kind of polymer in such a way that the grooves are in the same direction of the polarized film. On top of this glass spread a layer of pneumatic liquid crystal and when the right angle is visible add the second piece of the glass filter. The glass filters are considered to be kept at right angles to each other.
While constructing a liquid crystal display device, there are several important things that have to be taken care of. The crucial one among these is that the light used in the operation must be a polarised one. The applied current should be able to control the basic structure of LCD.
Working: LCDs work on the principle of blocking light. When a light beam passes through the liquid crystal molecules, the molecules tend to untwist and it causes a change in angle of the light beam as well as in the polarized glass filter. This results in no light to pass through a particular area of the LCD and this area looks darker.
Consider the situation when the light reaches the other piece of glass which is attached to a rectangular electrode on the bottom and a polarizing film on top of it. Consider that two pieces are kept in right angles. When the electrode is not connected to a battery, that is when there is no current supply, the light will be reflected by the mirror and bounced back. When the electrode is connected to a battery, the current supply causes the liquid crystal to untwist and this will block the light from passing through it. This causes the particular rectangle area to be appeared dark.
Ever since it’s inception, liquid crystal displays have been well-accepted among electronic equipment manufacturers. Character LCDs have already been a part and parcel of many day-to-day electric equipment and devices. The main reasons behind this high degree of acceptance are the low power consumption feature of the LCD devices. The LCD monitors are ultra thin and lightweight and can even mount on a wall. The applications range from simple calculators to sophisticated medical equipment. Many electronic devices which are being used at kitchen make use of character liquid crystal modules.
Advantages of an LCD
- Low power consumption
- Heat emission during operation is minimized owing to low power consumption.
- Low cost and ultra-thin appearance of LCD modules.
- It can be made in any size and shape.
- No flicker or minimum flicker
- When many LCDs with a different resolution are incorporated in a single application, each additional LCD adds to the total resolution and this is called ‘stacked resolution’. This is a welcome feature in many applications.
- Higher image quality due to masking effect which is the quality of masking the grey scale and spatial quantization.
Disadvantages of an LCD
- Brightness distortion may happen due to uneven backlighting in some monitors. it happens as the monitor ages or if it is cheap
- It requires additional light sources for proper operation
- Limited temperature range
- It works at comparatively lower speed
- They require an AC drive for working
- It is really difficult to read the letters and numbers displayed on an LCD when you wear a polarized sunglass
- Contrast is very low in high-temperature environment