LCD displays
(88)The principle of operation of a monochrome liquid-crystal display (LCD) manufactured using the STN technology is based on a change in the polarisation of light caused by a change in the orientation of liquid crystal molecules under the influence of an electric field between the electrodes.
LCD – design of a monochrome liquid crystal display
An SNT liquid-crystal display consists of:
- Electrodes arranged on glass substrate – their configuration corresponds to the number and shape of pixels or graphic elements.
- Analyser and polariser (usually in the form of thin adhesive films).
- Backlit or mirror surface.
An STN LCD does not emit light like an LED display does, but transmits the light emitted by the backlight (transmissive displays) or reflects the light that reaches the display surface (reflective displays). In an LCD, the light is initially vertically polarised using a polarising filter. It then passes through a transparent electrode and a layer of liquid crystal. The electrode is shaped in a special way, so that when the voltage is switched off, the polarisation of the light is rotated by 90°. When voltage is applied, the electric field forces the molecules in the liquid crystal layer to rearrange in such a way that it does not rotate the polarisation of light. In this way, light is not transmitted through an analyser, which, depending on whether it is a positive or negative display, produces a black or transparent effect.
Types of LCDs (liquid-crystal displays)
The basic division of liquid-crystal displays derives from the type of information displayed. Depending on the number of liquid-crystal elements (pixels) and their arrangement, an LCD may display digits, alphanumeric characters or graphic symbols. Positive LCDs display dark characters against a light background, while negative LCDs display characters in the colour of the backlight against a dark background.
An LCD may feature a built-in controller and communicate with the environment via a digital interface. It may also include a built-in command interpreter and be controlled using special commands sent by a master system. These are usually graphic displays and alphanumeric displays. The simplest models of digital displays have no built-in controller and must be controlled by an external circuit.
Criteria for choosing the right liquid-crystal display (LCD)
When choosing a liquid-crystal display for your application, you should first pay attention to the type of displayed information and environmental conditions in which the LCD device will be used. The ambient temperature range and ambient lighting are particularly important, as some LCD models are not suitable for use in low or elevated temperatures. Considering the performance of today's microcontrollers and their associated peripheral modules, the type of interface and control method is less important. Other issues you need to consider are the type of connector, LCD mounting method, type of user interface (if you plan to use a touchscreen interface) and power supply parameters.
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