In
this article I have given detailed description about different types of
display devices and their working along with their comparison with
other display devices.
1. Planer devices
2. Non-planer devices
Planer devices
In planer devices the whole readable characters are arranges in a same plane in a sequential or non-sequential manner. Some example best suiting this category are segmental type devices, dot matrix type display that use rear projection and gaseous discharge segmental display.
Non-linear devices
Here displaying characters are arranged in different planes just opposite from linear devices. Some example illustrating non-linear devices are gaseous discharge tube and those using Lucite sheet.
In 7 segmental displays, there are 7 segments so arranged in a single plane such that activated segments form a numerical. All the numerical characters from 0 to 9 can be displayed by activating a group of segments. Each segment can be lightened or activated on application of small amount of voltage to them around 12.48V and requires small current as low as 10 to 50 mA. Here, the segments are generally LEDs (Light Emitting diode).
Its working principle is that when a gas is made to break down, by application of potential difference across it, it produces luminescence. A common anode is places there, made of gauge electrode that provides a positive potential to all the segments while each segment is provided with a separate cathode electrode. As, each segment is shaped in a numeral, on application of a negative potential to any them results in luminescence of the corresponding character from 0 to 9. All the electrodes are comprised in a sealed glass envelope filled with discharge gas within it such that the electrodes are made to have contact with pins mounted at bottom of the tube. It is possible to have a desired colour of the luminescent characters just by selecting a correct gas, for example neon gas is generally used for red-orange glow.
It is the advantage of nixie tubes that is involves simple circuitry as compared to other display devices and gives greater brightness. It requires comparatively larger voltage for its operation and also consumes greater amount of power.
Modern nixie tubes
There are several constructions available in modern nixie tubes. In conventional tubes there are only 10 cathodes representing only numerals from 0 to 9 but in modern nixie tubes there are 15 electrodes that are capable of displaying other signs, too, like +, -, and many more.
• It can work upon small voltage
• Uses less power
• More efficient
• Small size
• Versatility in luminescence colour
• Easily availability
It is just a PN junction diode with the added feature of emitting light on application of proper voltage across it. When, current is made to pass through it, electrons moves from N-region towards P-region and holes moves from P-region to N-region, as they are energised by external source. At junction both electrons and holes recombines together and settles down to lower energy state while emitting extra energy in form of electro-magnetic radiation. Frequency of these EM radiations, in case of LEDs, falls in visible region leading to emission of light from the junction on the account of recombination of charge carriers. The cathode electrode is deposited at bottom part of the LED, usually of gold while the anode is deposited at two extreme edges of the top to allow exposure of maximum area for emission. Different semiconductor materials are used for making LEDs emitting different colours, some of them are:
• Gallium arsenide phosphide (GaAsP) produces red or yellow light.
• Gallium arsenide (GaAs) emits red or green light.
They are used in segmental devices and dot matrix devices placed in a sequence so as to make it capable of producing all the characters by using their specific combination. A transistorized circuit can be used to drive individual LEDs such that on application of appropriate base current transistor gets saturated and provides required current to the concerned LED segment.
2. As the technology used for making LEDs is same that is used for other usual components like transistor and integrated circuits, thus its manufacturing comes out to very economical.
3. Different colour can be obtained from LEDs like red, green, yellow and white.
4. They are highly efficient as they uses only a small amount of power for production of light as a very small amount of energy is wasted as heat. It requires voltage and current in rage of 1.2V and 20 mA to produce its full brightness.
5. As the brightness depends upon the current flowing through it, so it is very to control the brightness of LEDs by means of controlling the current flowing through it.
6. A very important feature of LED is that it has a very small switching time in range of ns.
7. Having rugged nature vibrations and shocks imparts no effect over LED.
2. It cannot be employed in large area as in that case it will be costlier.
1. Dynamic scattering LCD
2. Field effect LCD
Dynamic scattering LCD
It uses a liquid crystal material that exhibited the optical properties while being in liquid state itself which is organic material in nature. This liquid crystal is layered between two transparent glass sheets such that their inner face is pasted with a transparent electrode for the sake of making electrical contact with the liquid crystal. On application of a potential difference across the two electrodes it disturbs the alignment of the molecules in crystal material. In normal situation when no potential is applied to the cell it appears to be transparent i.e. light falling upon the cell passes through liquid material but as soon as potential difference is applied turbulence produced in molecular alignment causes the cell to appear bright as light entering it gets scattered and does not succeed to pass through it. It is to be emphasized that it does not produce own luminescence but depends upon some external light source.
Field effect LCD
It is similar to that of a dynamic scattering cell on basis of its construction but in this case polarizing optical filter are also place at inside of each glass plates. And, also, the liquid crustal material is of deferent form than employed in dynamic scattering cell, it is twisted nematic type that twists the light passing through it, when no electric field is applied to cell. This twisted light easily passed through the polarising filters. Thus when cell is enlightened by a light source at rear position all the light passed through it making it bright. As soon as, a cell is subjected to a potential difference no twisting of light takes place, as a result it becomes dull.
2. They are also cheap as compared to other electronic devices.
2. They work well upon AC supply and DC power reduces it life span. Typical frequency used for their satisfactory operation is 500 Hz.
3. A larger area is occupied by them.
Display Devices
Display device, that is used to display some visible massage, may have several types depending upon several criteria. One criterion for their classification is formatting of the display, thus there can be two type of display devices based upon the format are:1. Planer devices
2. Non-planer devices
Planer devices
In planer devices the whole readable characters are arranges in a same plane in a sequential or non-sequential manner. Some example best suiting this category are segmental type devices, dot matrix type display that use rear projection and gaseous discharge segmental display.
Non-linear devices
Here displaying characters are arranged in different planes just opposite from linear devices. Some example illustrating non-linear devices are gaseous discharge tube and those using Lucite sheet.
Segmental display devices
These may be 7 segmental or 14 segmental types whose requirement is decided by its application i.e. 7 segmental for numerical displaying and 14 segmental for Alfa-numeric display use. In 7 segmental displays, there are 7 segments so arranged in a single plane such that activated segments form a numerical. All the numerical characters from 0 to 9 can be displayed by activating a group of segments. Each segment can be lightened or activated on application of small amount of voltage to them around 12.48V and requires small current as low as 10 to 50 mA. Here, the segments are generally LEDs (Light Emitting diode).
Fourteen segmental display devices
These are used as advanced version of seven segmental display devices as these are capable of displaying Alfa-numeric characters. They also work in the same way as seven segmental devices where each segment is special purpose LED and lightening a group of segment altogether results in formation of a desired character that can be a numerical or an alphabet.Dot matrix display
These devices use dots in place of segments in segmental displays. Where dots mat acquire any shape i.e. round or square of diameter in range 0.4 mm. Depending upon the number of dots used it can be 3X5 dot matrix or 5X7 dot matrix.Rear projection display
This type device uses 12 incandescent lamps mounted at the rear portion of display system. There are different strips placed at front region which are illuminated by the incandescent lamps giving rise to a specific pattern upon the screen. A lens system is used to focus the light come from the lamp onto the viewing screen. It requires less amount of voltage between 6.3 V to 28 V and consumes power from 1 W to 3W. On other hand nixies tubes uses 170V to 300V for its operation and consumes power of about 0.5 W.Nixie tube
It is a non-planer device as it involves the display characters present in different planes. It is a gaseous discharge device having numeral shaped into different characters placed in different plans and mounted with electrodes. It is also called as cold cathode glow discharge tube.Its working principle is that when a gas is made to break down, by application of potential difference across it, it produces luminescence. A common anode is places there, made of gauge electrode that provides a positive potential to all the segments while each segment is provided with a separate cathode electrode. As, each segment is shaped in a numeral, on application of a negative potential to any them results in luminescence of the corresponding character from 0 to 9. All the electrodes are comprised in a sealed glass envelope filled with discharge gas within it such that the electrodes are made to have contact with pins mounted at bottom of the tube. It is possible to have a desired colour of the luminescent characters just by selecting a correct gas, for example neon gas is generally used for red-orange glow.
It is the advantage of nixie tubes that is involves simple circuitry as compared to other display devices and gives greater brightness. It requires comparatively larger voltage for its operation and also consumes greater amount of power.
Modern nixie tubes
There are several constructions available in modern nixie tubes. In conventional tubes there are only 10 cathodes representing only numerals from 0 to 9 but in modern nixie tubes there are 15 electrodes that are capable of displaying other signs, too, like +, -, and many more.
Light Emitting Diode
LEDs are taken onto use in most of the modern display as they have certain characteristics like:• It can work upon small voltage
• Uses less power
• More efficient
• Small size
• Versatility in luminescence colour
• Easily availability
It is just a PN junction diode with the added feature of emitting light on application of proper voltage across it. When, current is made to pass through it, electrons moves from N-region towards P-region and holes moves from P-region to N-region, as they are energised by external source. At junction both electrons and holes recombines together and settles down to lower energy state while emitting extra energy in form of electro-magnetic radiation. Frequency of these EM radiations, in case of LEDs, falls in visible region leading to emission of light from the junction on the account of recombination of charge carriers. The cathode electrode is deposited at bottom part of the LED, usually of gold while the anode is deposited at two extreme edges of the top to allow exposure of maximum area for emission. Different semiconductor materials are used for making LEDs emitting different colours, some of them are:
• Gallium arsenide phosphide (GaAsP) produces red or yellow light.
• Gallium arsenide (GaAs) emits red or green light.
They are used in segmental devices and dot matrix devices placed in a sequence so as to make it capable of producing all the characters by using their specific combination. A transistorized circuit can be used to drive individual LEDs such that on application of appropriate base current transistor gets saturated and provides required current to the concerned LED segment.
Advantages of LEDs
1. Having small size they can be miniaturized according to display devices like dot matrix and capable of displaying desired character in high density matrix.2. As the technology used for making LEDs is same that is used for other usual components like transistor and integrated circuits, thus its manufacturing comes out to very economical.
3. Different colour can be obtained from LEDs like red, green, yellow and white.
4. They are highly efficient as they uses only a small amount of power for production of light as a very small amount of energy is wasted as heat. It requires voltage and current in rage of 1.2V and 20 mA to produce its full brightness.
5. As the brightness depends upon the current flowing through it, so it is very to control the brightness of LEDs by means of controlling the current flowing through it.
6. A very important feature of LED is that it has a very small switching time in range of ns.
7. Having rugged nature vibrations and shocks imparts no effect over LED.
Disadvantages of LED
1. However, LED requires higher power for it operation as compared with LCDs that uses power in range of microwatts.2. It cannot be employed in large area as in that case it will be costlier.
Liquid crystal diode
They also have similar application like LEDs i.e. for showing numerical and alphanumerical figures with help of dot matrix display and segmental display.Types of LCDs
On the basis of the working of the device it can be classified into two categories as:1. Dynamic scattering LCD
2. Field effect LCD
Dynamic scattering LCD
It uses a liquid crystal material that exhibited the optical properties while being in liquid state itself which is organic material in nature. This liquid crystal is layered between two transparent glass sheets such that their inner face is pasted with a transparent electrode for the sake of making electrical contact with the liquid crystal. On application of a potential difference across the two electrodes it disturbs the alignment of the molecules in crystal material. In normal situation when no potential is applied to the cell it appears to be transparent i.e. light falling upon the cell passes through liquid material but as soon as potential difference is applied turbulence produced in molecular alignment causes the cell to appear bright as light entering it gets scattered and does not succeed to pass through it. It is to be emphasized that it does not produce own luminescence but depends upon some external light source.
Field effect LCD
It is similar to that of a dynamic scattering cell on basis of its construction but in this case polarizing optical filter are also place at inside of each glass plates. And, also, the liquid crustal material is of deferent form than employed in dynamic scattering cell, it is twisted nematic type that twists the light passing through it, when no electric field is applied to cell. This twisted light easily passed through the polarising filters. Thus when cell is enlightened by a light source at rear position all the light passed through it making it bright. As soon as, a cell is subjected to a potential difference no twisting of light takes place, as a result it becomes dull.
Transmittive type
In this type cells have both the glass plates transparent in nature so that light coming from a rear source gets scattered onwards.Reflective type
In this case one glass is kept completely transparent while bottom glass is pasted with a reflective material so as to make the light coming from front source get reflected back making the cell appear bright. As LCDs works upon the principle of reflection or transmission of light only and does not tend to produce its own light it consumes lesser amount of energy for its operation. As compared to 7-segment display devices it works upon smaller current in range of 25-300 micro A in dynamic and field effect type cells respectively. They require AC voltage for it operation unlike LEDs which works upon DC voltage.Advantages of LCD
1. Its power consumption is very low when compared with LEDs which is in range of micro watts (about 140 micro watts) in seven segment device.2. They are also cheap as compared to other electronic devices.
Disadvantage of LCD
1. Unlike LEDs these have a large turn off and turn on time i.e. they take longer time to change it state from on state to off state. The switching time is in range of milliseconds. This disadvantage makes it inappropriate for fast display devices.2. They work well upon AC supply and DC power reduces it life span. Typical frequency used for their satisfactory operation is 500 Hz.
3. A larger area is occupied by them.
Really- very important tips.................
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