Till now, we have spoken only about the output of the 7 Segment Display. You can see how numbers from ‘0’ through ‘9’ will look on a typical 7 Segment Display in the following image. For example, to display the number ‘0’, all the segments must be ON except the segment ‘G’. To display a particular number, you have to turn ON or OFF a group of Segments. You can see in the following image the side-by-side representation of a typical 7 Segment Display and it Segment names. It is technically an 8 Segment Display with 7 Segments responsible for displaying the main numerical data and one dot segment. Most 7 Segment Display have an additional segment in the form of a dot. The name ‘7 Segment Display’ means that it has 7 LEDs in the form of hexagonal bars that are arranged in the form of ‘8’.Įach LED is known as a ‘Segment’ with names A, B, C, D, E, F and G. The cells with square waves in antiphase with the back plane input have a square wave with peak voltage 2V P developed across them, consequently, they are energized.A 7 Segment Display is one of the simplest types of display devices that can display numbers from 0 through 9 (you can also display characters from ‘A’ through ‘F’). Both terminals of the segment are at the same potential, so they are not energized. Those cells with waveforms in phase with the back plane waveform (cells e and f in Figure 20-9) have no voltage developed across them. Similar square wave applied to each of the other terminals are either in phase or in antiphase with the back plane square wave. The back plane, which is common to all of the cells, is supplied with a square wave, (with peak voltage V P). Figure 20-9 illustrates the square wave drive method. Repeatedly reversing the current avoids this problem.Ī typical LCD supply is a 3 V to 8 V peak-to-peak square wave with a frequency of 60 Hz. This is because a continuous direct current flow produces a plating of the cell electrodes that could damage the device. However, LCDs require an ac voltage supply, either in the form of a sine wave or a square wave. The total current flow through four small LED Seven Segment Display is typically about 20 μA. The only energy required by the cell is that needed to activate the liquid crystal. LCD Seven-Segment Display:īecause liquid-crystal cells are light reflectors or transmitters rather than light generators, they consume very small quantities of energy. The trans-reflective cell is a combination of transmittive and reflective types. When energized, the light is blocked, and here again the cell appears dark against a bright background. 20-8(b) allows light to pass through from the back of the cell when not energized. When energized, no light is reflected from the cell, and it appears dark against the bright background. The cell is placed on a reflective surface, so that when not energized it is just as reflective as the surrounding material, consequently, it disappears. Two types of LCDs are illustrated in Fig. Seven-segment numerical (and other type) displays made from liquid crystal cells are referred to as liquid crystal displays (LCDs). The cells can also be manufactured to appear bright against a dark background. Thus, the energized cell can appear dark against a bright background. When energized, the liquid molecules are reoriented so that no twisting occurs, and no light can pass through. This twisting allows the light to pass through the polarizing filters, so that the cell is semi-transparent. The liquid-crystal material employed twists the light passing through when the cell is not energized. In the commonly used twisted nematic cell two thin polarizing optical filters are placed at the surface of each glass sheet. The glass sheets have transparent metal film electrodes deposited on the inside surfaces. In liquid crystals the molecules are oriented in a definite crystal pattern.Ī liquid crystal cell consists of a very thin layer of liquid crystal material sandwiched between glass sheets, as illustrated in Fig. The molecules in ordinary liquids normally have random orientations. Liquid crystal material is a liquid that exhibits some of the properties of a solid. Apart from this, LEDs have the advantage of long life and ruggedness. The relatively large amounts of current consumed by LED seven-segment displays are their major disadvantage. When selecting a LED seven-segment display, it is important to determine which of the two connecting arrangements is required. The LED Seven Segment Display may be connected in common-anode or in common-cathode configuration.
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