LCD type

LCD type

Due to its limitations, TN liquid crystals are only used to produce character-type liquid crystal modules; while STN (DSTN) liquid crystal modules are generally small and medium-sized, both monochrome and pseudo-color; TFT liquid crystals, from small to large Yes, and almost all of them are true color display modules. In addition to TFT LCDs, generally small LCD screens have a built-in controller (the concept of the controller is equivalent to the main control chip on the display card), which directly provides MPU interface; while large and medium LCD screens, if you want to control its display, you need to add Controller.

If you only need to display characters and numbers, and the content displayed on one screen does not exceed the maximum limit of the character LCD (for example, 40×4), you can choose the character LCD and connect directly to the MPU. If you need to dynamically display Chinese characters and graphics, then choose graphic dot matrix liquid crystal, choose STN (DSTN) monochrome, false color or TFT true color. In general, if you use a single-chip microcomputer to control, due to its control ability, you can only choose within the range of monochrome below 640×480 and pseudo-color below 320×240; if you use PC, IPC or other masters with strong control capabilities The control module (such as the video input control module), as long as it has a liquid crystal display part or an external display control, can have a larger choice. Monochrome, pseudo-color and true-color liquid crystals without a built-in controller are available. At the same time, the external dimensions should be considered. Please also note that the resolution of LCD is physically fixed, and full-screen display can only be displayed at its inherent resolution, which is different from CRT.

There are three types of backlight options: transmissive, reflective, and transflective liquid crystal. Because liquid crystal is a passive light-emitting display, it must have an external light source for the liquid crystal to display. Transmissive liquid crystal must be added with background light, reflective Liquid crystals require strong ambient light, and transflective liquid crystals require strong ambient light or backlight. Character type liquid crystal The backlight is generally LED backlight, mainly in yellow (red and green tones). It is generally driven by +5V. Monochrome STN small and medium dot matrix liquid crystals mostly use LED or EL backlight. EL backlight is usually yellow-green (red, green, white tones). Generally use 400-800Hz, 70-100V AC drive, common drive requires about 1W of power. Medium and large dot matrix STN liquid crystals and TFT liquid crystals are mostly cold cathode backlight tubes (CCFL/CCFT), and the backlight color is white (red, green, and blue tones). Generally use 25k-100kHz, AC drive above 300V.

The simple matrix driving method is composed of vertical and horizontal electrodes. The selected part to be driven is controlled by the horizontal voltage, and the vertical electrodes are responsible for driving the liquid crystal molecules. In TN and STN type liquid crystal displays, the method of using simple driving electrodes is driven by the intersection of X and Y axes. The driving method of active matrix is to let each pixel correspond to a group of electrodes. The structure is a bit like the loop method of DRAM, and the voltage is scanned (or called charging for a certain period of time) to indicate the state of each pixel.