Features of choosing a character LCD indicator
When choosing a symbolic (sign-synthesizing) indicator, one should be based on two considerations:
- the size and format of the module required to display information;
- optical characteristics for optimal vision of the displayed information and ease of use.
You should also keep in mind that character modules display numbers, letters, and some limited graphics. The interface is organized, as a rule, through a bidirectional parallel ASCII data bus. In principle, character display modules are the simplest and most economical means of communication between any microsystem and a human.
Character modules can have from 8 to 80 characters per line with a choice of displays with one , two or four character lines. It should be borne in mind that if you need to display more than 4 lines, or more than 40 characters per line, it is better to use graphic displays. Especially if there is a need to generate characters that differ in size, or characters with special fonts.
The number of characters per line, as well as the number of lines, is displayed in the module name. So, for example, modules containing the combination " 1602 " in the name have 16 characters per line and two lines. Modules with the combination " 2004 " in the name have 4 lines, each of which can display 20 characters.
One of the main parameters of character displays is the so-called. "visible" area. In other words, the length and width of the matrix itself that displays the characters, as well as the overall dimensions of the module itself. And this should not be neglected, because. within the same format, several constructs can be produced, differing both in the dimensions of the LCD (as a result, in the size of the characters), and in the dimensions of the board and fit.
Further, the choice of the optimal version of the LCD indicator, even within a given format, depends on many determining factors. Color, type of liquid crystal material, type of backlight - all this affects the nature of the work with the display. Also, factors influencing the determination of the type of display are the environmental conditions in which the final product will be operated - ambient temperature, lighting conditions, power consumption, etc.
The liquid crystal material type determines the contrast, viewing angle, and operating temperature range. There are three types of liquid crystals used in LCDs - TN, NTN and STN types. TN type liquid crystals are the simplest material used in the manufacture of LCD displays. Crystals of NTN and STN types are characterized by higher contrast with a wider viewing angle. The main ratios corresponding to different types of liquid crystals are shown in the table.
|Material type||Sample Contrast||Typical viewing angle|
There is also a modified STN technology - FSTN. The difference from STN-matrix technology is that FSTN-matrices have a special film on the outside that allows you to compensate for color shifts from blue to green to black to white, as well as improve the viewing angle.
In addition, it must be borne in mind that the viewing angle may not be directed perpendicular to the indicator plane, but shifted to the upper, lower, left or right area (offset angle). The offset angle orientation of displays is often formulated in terms of reference directions of the dial of an analog clock. If the direction of best view is above the display, the 12:00 offset or main offset is said to be. If the direction of the best view is below the display, then such an offset will be indicated as "6:00".
The next parameters needed when choosing a display are the display modes. There are so-called. "positive" and "negative" display modes. In positive mode, the display shows "dark" characters on a light background. In the negative mode, on the contrary, “light” characters on a dark background.
In addition, LCD indicators are divided into three types - reflective (reflective), transparent (transmissive) and semi-reflective (transflective).
Reflective displays are equipped with total reflection reflectors. They do not use backlighting. They have the lowest consumption, have the highest contrast in high ambient light conditions, and are only available in negative display mode. Transparent displays usually have a "negative" display mode. Backlighting is used for better readability. These displays are typically used in low light conditions. They are not recommended for use in direct sunlight. Semi-reflective displays combine the qualities of reflective and transparent displays. These "positive" displays ensure readability in all light conditions. When the lighting is poor, the backlight can be turned on, when the light is good, the backlight can be turned off, which will help reduce consumption.
And finally, the backlight. EL (electroluminescent) backlight is the main LCD backlight. The EL design of the backlight is thin, light, the backlight itself has low consumption, and is placed between the glass assembly and the printed circuit board without any change to the display module itself. Most positive-image displays use blue-green lamps; negative-image displays typically use white lamps. It is necessary to pay attention to the fact that the brightness of the lamps and their service life are inversely proportional - with an increase in brightness, the service life is shortened (decreasing the brightness to half of the original). Light-emitting diode (LED) backlight has a significantly longer life than electroluminescent lamps, but its use leads to an increase in consumption and an increase in module size. It is not recommended to use them in battery powered applications where it is necessary to have the backlight always on.