The working principle of an LCD screen is based on the interaction between the optical properties of liquid crystal molecules and the control of an electric field. Its core is to change the arrangement of liquid crystal molecules through an electric field, thereby controlling the transmission or blocking of light to achieve the display function. The following is a detailed explanation of the specific principle:
Optical Properties of Liquid Crystals: Liquid crystals are special substances between solid and liquid states, and their molecular arrangement is directional. When light passes through liquid crystals, the path is twisted or blocked due to the molecular arrangement. For example, without an applied electric field, the liquid crystal molecules are arranged regularly, allowing light to pass through; after applying an electric field, the molecular arrangement is changed, and the light may be twisted or completely blocked.
Electric Field Control of Molecular Arrangement: The core structure of an LCD consists of two layers of transparent electrodes (such as indium tin oxide, ITO) and a liquid crystal layer sandwiched in between. When a voltage is applied to the electrodes, the electric field changes the alignment direction of the liquid crystal molecules. For example:
TN Type (Twisted Nematic): Without an electric field, the liquid crystal molecules are arranged in a helical pattern. Light is twisted 90 degrees after passing through a polarizer and then through another polarizer, displaying a bright state; after an electric field is applied, the molecular arrangement becomes perpendicular, and the light is blocked, displaying a dark state.
IPS (In-Plane Switching): Controls molecular rotation through a horizontal electric field, offering a wider viewing angle but requiring a higher driving voltage.
Backlighting and Display: LCDs themselves do not emit light and rely on a backlight module (such as LEDs) for illumination. Light passes through the liquid crystal layer and is filtered by color filters to form red, green, and blue (RGB) sub-pixels, which combine to create a color image. For example, each pixel consists of three sub-pixels, and color mixing is achieved by controlling the transmittance of each sub-pixel.
Driving Methods:
Dedicated Driver IC: Common driver chips (such as the 1621) control liquid crystal molecules through alternating positive and negative waveforms, preventing direct current from causing molecular immobilization (electrochemical degradation). For example, TN LCDs require alternating positive and negative voltages to extend their lifespan.
Microcontroller Analog Driver: Simple LCD screens (such as dot-matrix screens displaying only numbers) can directly use microcontroller I/O ports to simulate waveforms, reducing costs, but it is necessary to ensure that the waveform frequency and amplitude meet the requirements of the LCD.
Environmental adaptability optimization is crucial. Low temperatures can slow down the response speed of liquid crystals, requiring solutions such as heating modules or the use of low-temperature resistant materials. High-definition display requirements necessitate increased backlight brightness or the use of LED screens. For example, outdoor instruments need to operate normally in environments below -20°C, necessitating the selection of wide-temperature-range liquid crystal materials.
In summary, LCDs achieve image display by controlling the alignment of liquid crystal molecules through an electric field, combined with backlighting and color filters. The driving method must be matched to the liquid crystal type, and environmental adaptability must be considered to optimize performance.
