User:Jimmykraemer/sandbox/Dot-matrix display

A Dot-matrix display is type of art or information display device consisting of an array of small lights or mechanical dots. Letters, numbers, and graphics can be displayed by controlling which dots are "on" and which dots are "off". The most commonly used dots are made from Liquid-crystal displays (LCD's) or Light-emitting diodes (LED's), and other displays can use physical dots instead of lights. A cross circuit pattern with a dot at each intersection is what controls the "on" and "off" state of the dots.

This type of display is typically used to display small amounts of information, such as numbers on a calculator or the time on a digital clock. Large displays can be used to effectively show information to a lot of people at once, such as departure and arrival times at an airport. Various art pieces have been made with dot-matrix displays, and the development of LED displays has led to the development of flat screen televisions.

History

Liquid crystal was discovered in the late 1880's, first referred to as "flowing crystals". More than 200 chemical compounds were discovered that had liquid crystal-like behavior by the early 1900's, but research on the electrical applications did not start until the early 1960's.

The first commercial LCD was invented in 1968 by George Heilmeier and his group of scientists from the RCA corporation. At the time, only Cathode ray tube (CRT) displays were around, which required thousands of volts to power and took up a lot of space. The LCD provided a lower power, less bulky alternative to the CRT display. Patents for the first dot-matrix LCD displays date back to the 1970's and 1980's.

The concept of Electroluminescence, the phenomenon that light is emitted from certain materials when an electric current is passed through them, was first discovered in 1907, which is the basis of LED's. This led to the development of LED's that produce infared light in the 1950's, and the first LED to produce light in the visible spectrum was invented in 1962, which was red light.

Progress on the development of color displays using visible light LED's was halted until LED's in multiple colors were produced. The blue LED, which would complete the trio of colors needed to make a color display, was not invented until the 1970's, and was not very efficient until the 1990's. Patents for color LED displays appeared shortly after.

Mechanism

A basic circuit diagram of the cross-pattern circuit commonly used in a LED dot matrix display. Each LED can be powered by powering its corresponding row and column lines. The bottom-left LED, for example, is powered by powering column A and row C.

Most dot-matrix displays use a cross pattern of circuit lines to control which dots are illuminated, in a coordinate style. A transistor, which is what illuminates each dot, is placed at each intersection of vertical and horizontal circuit line. The dot is illuminated if electricity is sent through the vertical and horizontal circuit lines that intersect at that dot's transistor. Different types of displays differ in the types of dots that are illuminated.

LCD panels

A basic backlit LCD display on a keyboard

LCD's work because of the properties of liquid crystal. Liquid crystal is an organic liquid that has properties of both a liquid and a crystal. This allows the liquid to become opaque by orienting its molecules in a crystal structure, which can be achieved by passing electricity through it. The opaqueness of the liquid crystal can be changed by changing the amount of voltage passed through the liquid.

Displays made with liquid crystal are typically comprised of a bit of liquid crystal between two thin sheets of glass or transparent electrodes. The bottom electrode is reflective, which allows light to reflect off of it when the liquid crystal is in a transparent state, representing an "on" state.

The role of the transistor for LCD displays is to complete the circuit between the top and bottom electrodes, which causes electricity to flow through the liquid crystal, making the liquid crystal opaque. Color displays with this concept involve each "dot" being represented by a group of three separate liquid crystal dots, which are controlled independently. The color of the trio of dots can be adjusted by adjusting the opaqueness of each color dot.

LCD panels require very little energy and are clearly visible in daylight, but can be difficult to see in low-lit areas since liquid crystal itself does not produce light. To compensate for this, some designs for LCD displays have an additional light behind the liquid crystal (referred to as a backlight), so in the transparent state, that light can shine through and make the display easier to see in low lit areas.

LED panels

An up close image of a color LED display

LED's work because of p-n junctions. A p-n junction is a special part of a circuit that involves two pieces of a semiconductor, which is most commonly Silicon, that have their chemical properties changed by placing another element into each piece of the semiconductor. Most commonly, Phosphorus is placed into one piece and Boron is placed into the other. When two semiconductors with these extra elements are placed together, it creates a magnetic field, which restricts the flow of electricity to one direction. Additionally, passing electricity through this junction generates light, and changing the semiconductor material changes the color of the light produced.

The main difference between LED and LCD displays is that LED's produce their own light, which means they can be better seen in dark lighting situations than LCD displays. The ability to control the brightness of each LED dot also makes LED displays able to adjust for different lighting situations. Similar to LCD's, LED panels also require little energy, but their lifespan can be shorter than those of LCD's due to excess heat generation.

Color LED dot matrix displays work in the same way as LCD ones in the sense that they involve groups of three lights in red, green, and blue. However, colors are controlled in LED displays by adjusting the brightness of each color dot as opposed to the opaqueness in LCD displays.

Flip dot panels

A flip-dot display

A flip dot display (also called a "flip disk display") is a type of dot matrix display that uses small magnetic disks instead of lights. Each disk has a reflective side, representing the "on" state, and a dark side, representing the "off" state, and the shown side is controlled by an electromagnet.

Similar to LCD displays, the disks themselves do not produce light, which means the system mainly relies on other sources of light to be visible. Due to moving parts that require maintenance, these types of displays are not as preferred as LCD or LED displays, but are still widespread.

Applications

A dot matrix display used as a way to list departure times of a train in Luton

Dot matrix displays are often used in places where simple information needs to be displayed. Some examples of this include:

• Departure/Arrival time boards at airports and train stations
• Elevator floor indicators
• Calculator screens
• Digital clocks
• Arcade machine score displays
• Flat-screen televisions

An example of a dot matrix display used in the London Underground

External links

• www.example.com