Seven-segment display

A segment display is capable of displaying, by electronic or electromechanical control of individual or more of its segments letters, numbers or characters. There are many different types of gauges, which differ in the number and arrangement of their segments. The most important is the seven-segment display, which is used in digital watches and all the digits from 0 to 9 up to seven individual " strokes " composed.

An extension of these results in the display segment fourteen- segment display in which additional diagonal and vertical segments are included. Rarely it is running as a sixteen- segment display. These two -segment displays have the advantage of all uppercase letters of the Latin alphabet and some special characters such as " " and "* " to be able to reproduce well. In English, these ads are because of their appearance often called starburst display Union Jack British flag display or display.

Other developments have in some cases significantly more segments, for example 38, 88 or 111 in the widespread Geascript family of BMG / MIS. Especially the high readability ensures that this technique in certain niches, such as the parking control system, can compete with matrix displays with flexible design options.

Seven-segment display

A seven segment display is a display element from seven separately switchable, exposed beams, which are arranged in the form of two superimposed standing, often square rectangles. Normally, the small segments with the Latin letters A to G are designated, starting at the top, proceeding in the clockwise direction and the center segment is the last named.

It is primarily used to represent the decimal digits zero through nine, for example, in calculators and digital watches, but also partly on non- electronic scoreboards, for example for lottery jackpots. The representation of the digits is abstracted here, so not quite perfect in comparison to "normal" font ( the most significant examples are the numbers 4 and 7). The ubiquity of Siebensegementanzeigen this abstraction falls in daily life any more.

In addition, a point of the paragraph is left or right often integrated as a comma character. This special segment is often referred to as DP for decimal point.

From a ½ - point occurs when only the segments b and c, and a plus sign are integrated. This can then be 0 ( = off), the number 1, and and - represent, for example, ads to 1999 From a ¾ digit is when the numbers 1, 2, 3 as well as can be displayed. for example, in displays to 3999th

Since most systems today work with a data width of 8 bits or multiples of that, there are at most display elements an eighth "element" in the form of a point on the base line to the right of the segment d (right, because there due to the mostly cursive orientation the character more space than is left ). The point is driven via an eighth data bit and mostly used as a decimal separator, but is also used quite differently depending on demand.

History

Already on June 17, 1908, Frank W. Wood has patented an eight- segment display, the additional diagonal segment to represent the digit four contained ( U.S. Patent number 974.943, issued on November 8, 1910). Further distribution segment displays found only in the 1960s with the advent of fluorescent and LED displays. Before the breakthrough of LED technology there was in the 1970s precursor in the form of numeric display tubes in filament technique - " Numitrons " ( in tubular housings ) and later " Minitrons " ( in plastic cases like the later LED versions ) - or as a gas discharge tube.

Representation

The presentation of letters ( Latin, Greek, Cyrillic) is limited. A good legibility can be achieved by use of mixed upper and lower case letters. In order to represent hexadecimal digits can be, for example, the letters , , E and F units represent relatively well.

For some numbers, there are variants with a segment more or less: a in the <6> f < 7> and d < 9>. In safety- critical areas of a design is useful where the failure of any segment does not mean that a digit looks like another ( for example, < 9> or < 6> to <5 > ), but the defect is noticed. In addition, preferences from the locally usual handwriting can be crucial.

Other large letters that can be mapped recognizable, are , I, and possible lowercase letters are , < j >, , and the sign of

/

and / see for majuscule and minuscule from identical. <- > Special characters, inter alia, the minus sign can, the underscore <_> and simplified quotes <" > are shown.

Some letters look exactly like the digits, for example or / / as <9 >, < 1>, <0 >, < 5 >, < 2 >. The remaining can be displayed only with difficulty with the seven segments, especially / , / , / , < W> / and / , as can the middle or diagonal lines depict not good. Even characters with diacritic as German umlauts < Ä >, < Ö > and < Ü > cause problems. In part, there but perfectly acceptable Behelfsdarstellungen, for example, for the open and .

Examples

Done in some CD players status information about a seven-segment display:

Control

The segments are now made ​​mostly from light emitting diodes ( LEDs) or liquid crystal displays (LCDs). For very large-format displays are also fluorescent tubes to form the segments in use.

For the control of seven-segment displays of LEDs or LCDs usually integrated seven-segment decoder circuits ( ICs) are used, which binary coded numbers (4 bits ) to transcode to seven bits for driving the seven segments. In discrete clocks of the 1970s, the types ending in 47 or 247 come with TTL and CMOS compatible modules (Series 74L ..., ... 74LS, 74HC ... ) are usually used. In the standard CMOS series (eg, CD ... ) it's the guy with the last digit 4511th

Figures from a plurality of digits can be driven with the aid of the time-division multiplex method, which is not a further decoder circuit is required for each digit. A disadvantage is the flicker.

Since the 1990s, partly a programmable microcontroller replaces the previously required large numbers of ICs with smaller displays, but BCD -to- 7-segment decoder, the number of required I / O ports can be reduced to the Microcontroller with one. For larger LED displays direct control with microcontrollers is often not possible because the outputs can not muster enough power.

Control of several displays with microcontrollers

While the display of multiple digits with Counter ICs is fairly straightforward, the use of microcontrollers, the number of required I / O ports is critical. Thus, for example, a digital clock ( without second display) 28 LEDs (or 27, as the tens digit hours a segment not needed ). Even when driver ICs, the number is quite high with 16. Remedial action is taken by the common connection of a number is not permanently connected to the supply voltage, but the numbers are sequentially driven. Then the seven separate connections can be summarized by all digits. This / O ports are used for numerals I needed, so for a 4- digit digital clock eg 11 connections (see Multiplexer). Thus, a lower brightness is achieved, which can only be compensated by smaller series resistors. However, this can lead to damage to software problems with the display. This method also leads to a visible flicker when the display is filmed with television cameras (similar to the films of screens ).

Better, but more complex method is upstream of each digit, a driver IC with a built-in register ( for example, 4511 ). The microcontroller can then select the digit to be changed via the memory input and associated data lines change as described this.

Logic table

Suppose a 7 -segment display has four digital inputs for control. Then follows the numeric representation of the following assignment of the inputs ( x3, x2, x1, x0 ) for the seven segments (a, b, c, d, e, f, g):

Switching functions for the segments

The following switching functions in disjunctive normal form ( DNF ) arising from the above logic table:

If we restrict ourselves to the decimal digits, then the functions simplify:

Seven segment driver blocks that to 9 can view only the decimal digits 0, contain only the logical functions shown in the last section and show nonsensical character, if the hexadecimal A to F applied at the input.

Fourteen- segment display

The fourteen- segment display is mainly used for representation of the large letters of the Latin alphabet. Small letters can represent only conditionally.

The middle horizontal member of the seven-segment display is to g1 and g2, divided into two sub-segments. The two additional vertical segments in the horizontal center and the diagonal elements between corners and center are designated from top - left to bottom - right by h to m.

Sixteen segment display

With this display, you can also display additional characters and symbols, such as the% character

In addition to the display segments 14 and the upper and lower horizontal segments can be divided into A1 and A2, as well as D1 and D2.

Credentials

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