LCD Display
Introduction To LCD Display
LCD display consists of an array of tiny segments known as pixels that can be manipulated to present
information. As a result of this technology, many types of this displays are used in applications like calculator, watch,
messaging boards, clock, equipments, machines and a host of other devices that one can think of. Most of the Display types are reflective, meaning that they use only ambient light to illuminate the display.
Even displays that do require an external light source consume much less power than CRT devices.
An LCD basically consists of two glass plates with some liquid crystal material between them. The small size compared
to CRT makes it practical for applications where size, current consumption and weight are the main consideration in
electronics design.
A liquid crystal display is a thin, lightweight display device with no moving parts. It consists of an
electrically controlled light polarising liquid trapped in cells between two transparent polarising sheets.
The polarising axes of the two sheets are aligned perpendicular to each other. Each cell is supplied with electrical
contacts that allow an electric field to be applied to the liquid inside. Figure below shows the typical LCD modules which
will be able to display graphics or characters when interface with a microcontroller or microprocessor.


Before an electric field is applied, the long, thin molecules in the liquid are in a relaxed state. Ridges in the
top and bottom sheet encourage polarisation of the molecules parallel to the light polarisation direction of the
sheets. Between the sheets, the polarisation of the molecules twists naturally between the two perpendicular extremes.
Light is polarised by one sheet, rotated through the smooth twisting of the crystal molecules, then passes through
the second sheet. The whole assembly looks nearly transparent. A slight darkening will be evident because of light
losses in the original polarising sheet.
When an electric field is applied, the molecules in the liquid align themselves with the field, inhibiting rotation
of the polarised light. As the light hits the polarising sheet perpendicular to the direction of polarisation, all
the light is absorbed and the cell appears dark.
Transmissive and reflective LCD display
LCDs can be used in transmissive or reflective modes.
A transmissive LCD is illuminated from one side and viewed from
the opposite side. Activated cells therefore appear dark while inactive cells appear bright. The lamp used to
illuminate the LCD in such a product usually consumes more power than consumed by the LCD itself.
A reflective LCD, as used in pocket calculators and digital watches, is viewed by ambient light reflected in a mirror
behind the display. This type has lower contrast than the transmissive type, because the ambient light passes twice
through the display before reaching the viewer. The advantage of this type is that there is no lamp to consume power,
so the battery life is long.
Customized or standard LCD design
Figure below shows an example of a LCD display which has segments that can be controlled to show +/- signs, readings from
the 7 segment. It is interfaced to the PCB by using a rubber connector with carbon that connects the segments and COMs of
the LCD to the ports of a microcontroller. Most manufacturers have some standard design of LCD to choose from but if a
customized design is needed, one have to engage the LCD maker to make a customized tooling for the LCD. In this case, the
design will be uniqued and will only be sold to the dedicated designer.
In the application of the LCD, one needs to know the viewing angle of the users. The design have to be specified upfront
whether the viewing angle is 6 o'clock, 9 o'clock, 12 o'clock or 3 o'clock as this will affect the viewing angle of the
product that has been designed.
If cost is a major constraint in the electronics project that uses LCD display, it is normally advisable for
the designer to choose from the standard catalogues of the manufacturer and purchase it.
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