Segment Displays
A segment display is a form of electronic display device for displaying alphanumeric character decimal numerals that is an alternative to the more complex dot-matrix displays.
Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic devices for displaying numerical information.
In seven segments display, as its name indicates, is composed of seven elements. There are also fourteen-segment displays and sixteen-segment displays (for full alphanumeric); however, these have mostly been replaced by dot-matrix displays. Segment displays are
- Seven Segment Display
- Nine Segment Display
- Fourteen Segment Display
- Sixteen Segment Display
- Eighteen Segment Display
Seven Segment Display
A seven-segment display, or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays.
Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic devices for displaying numerical information.
A seven segment display, as its name indicates, is composed of seven elements. The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top, middle, and bottom. Additionally, the seventh segment bisects the rectangle horizontally.
Fig. 1 shows a seven segment display. It is used to display alphanumeric characters. It consists of 7 rectangular light emitting diodes designated by the letters a, b, c, d, e, f and g. Each LED is called a segment, because it forms a part of the character being displayed.
Fig. 2 shows a schematic diagram of a seven-segment display. In this circuit, the anodes of all the diodes are connected together to the positive terminal of the dc voltage source. The cathodes are connected to the external resistors. The external resistor is necessary to limit the current through the LED. By grounding the external resistors, we can form any decimal digit from 0 to 9.
For example,
- by grounding a, b, g, e and d, we can form the digit ‘2’ as shown in Fig. 3.
- Similarly, by grounding f, g and c, we can form the digit ‘4’ and so on.
- The digit 0 can be formed by grounding all the terminals except g.
A seven segment display can also display the capital letters, A, C, E and F. Besides this, it can also display the lowercase letters b and d.
There are two important types of 7-segment LED digital display.
1. The Common Cathode Display (CCD): In the common cathode display, all the cathode connections of the LED’s are joined together to logic “0” and the individual segments are illuminated by application of a “HIGH”, logic “1” signal to the individual Anode terminals. Circuit diagram is shown in Fig. 4.
2. The Common Anode Display (CAD): In the common anode display, all the anode connections of the LED’s are joined together to logic “1” and the individual segments are illuminated by connecting the individual Cathode terminals to a “LOW”, logic “0” signal. Circuit diagram is shown in Fig. 5.
Nine-Segment Display
A nine-segment display is a type of display based on nine-segments that can be turned on or off according to the graphic pattern to be produced. It is an extension of the more common seven-segment display, having an additional two diagonal or vertical segments between the top, middle, and bottom horizontal segments. This provides a minimal method of displaying alphanumeric characters.
Nine-segment displays were used to provide basic alphanumeric as shown in Fig. 6. It used to avoid confusions with representing numbers in electronic products such as calculators, electronic watches etc.
Dot Matrix Display
A dot matrix display is a display device used to display information on machines, clocks, railway departure indicators and many and other devices requiring a simple display device of limited resolution.
The display consists of a matrix of lights or mechanical indicators arranged in a rectangular configuration. The rectangular arrangements are called arrays of LEDs.
By switching ON or OFF the selected LEDs, text or Graphics can be displayed. A matrix driver or controller converts the instructions from a processor into signals which turns ON or OFF LEDs in the matrix, so as to obtain the required display.
A dot matrix controller converts instructions from a processor into signals which turns on or off lights in the matrix so that the required display is produced.
The common sizes of dot matrix displays are 128 × 16 (Two lined), 128 × 32 (Four Lined) and 192 × 64 (Eight Lined). While a common size for a character is 5 × 7 pixels. This is seen on most of the graphic calculators.
The dot matrix displays are used in Variety of applications such as rolling advertisement boards, railway timing, reservation charts, temperature indication outside observatory digital clocks, calculators, digital diaries, microwave oven etc. The display of alphabetic character is shown in Fig. 7.