Liquid Crystal Display

Task
Liquid crystal displays (LCD) can display numbers, characters and other symbols. They therefore serve as output units for electronic systems. They are used more and more frequently to replace conventional analog pointing instruments and indicator lights.

Function (principle)
The principle of liquid crystal displays is explained here using the example of a seven - segment display (see Figure). Between the glass plates (a) and (f) is a spacer (d) surrounding a thin layer of liquid crystal (e). Glass plate (a) contains transparent electrodes (segments) in the shape of the characters to be displayed.

Glass plate (f) contains the transparent counter-electrodes (h). If the current is now applied between the contact (g) of the counter- electrodes (h) and one or several contacts (b) of the segmented electrodes (c), the liquid crystal changes its optic characteristics between the counter-electrodes (f) and the live electrodes (c). If you now look in the direction of the arrow, the areas of the live electrodes (c) appear dark and can therefore be seen. All numbers and characters can be displayed by controlling the electrodes (c). The liquid crystal display also has two polarization filters (I). This type of LCDs have a better contrast and work with a lower voltage (approx. 1.5 - 5 V).

Other characters can also be displayed by choosing a different shape for the electrodes. The multifunction display (A1p13), for example, uses strips of electrodes. In this case, both glass plates (a) and (f) contain strips of electrodes. The strips on glass plate (a) are perpendicular to the strips on glass plate (f). This allows individual dots (pixels) to be actuated. If different points are actuated repeatedly and quickly enough one after another, almost any image can be displayed.