The displays which are used to displays alphabets as well as numeric characters in response to the electrical inputs are called alphanumeric displays. The LEDs are arranged in various ways in such displays. One such alphanumeric display uses 18 LEDs and called eighteen segment display. It is shown in the Fig. 1.
Due to the diagonally arranged LEDs such as j, h, m, k the character like Y, K, M etc. can be displayed with such a display. A separate LEDs are used for the Decimal Point (DP) and Colon Operator (CO).
The various alphanumeric characters are displayed by lighting up the LEDs located in specific positions.
In some types, arrays of LEDs are used. One such displays uses 5 columns and 7 rows of LEDs and is called 7 x 5 dot matrix display. The Fig. 2 shows the LED display and its circuit connections.
Depending upon the required character, the corresponding LEDs switched on, in this display. The Fig 3 shows the display of character M and Y with the help of 7 x 5 dot matrix display.
To improve the brightness of display, a dynamic display system is used. In this, the LEDs are not lit continuously but are sequentially lit by scanning in a ''vertical strobe'' or ''horizontal strobe'' mode. This is similar to ''running lights'' used in modern advertisements.
In the vertical strobe mode, a single row is selected at a time, the appropriate LEDs are energized in that row, and then the signal is applied to next row. On the contrary, in horizontal strobe mode, a single column is selected at a time.
Alphanumeric displays using LEDs employ a number of square and oblong emitting areas, arranged either as dot matrix or segmented bar matrix.
Alphanumeric LEDs are normally laid out on a single slice of semiconductor material, all the chips being enclosed in a package, similar to an IC, except that the packaging compound is transparent, and not opaque.
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