BY:

AASHISH JAIN S

Display Devices and Data Loggers

Display Devices

Display Devices A display device is an output device for presentation

of information in visual or tactile form (the latter used for example in tactile electronic displays for blind people).

(or)

Display devices are devices used for the visual presentation of information.

Display devices

Planar display devicesAll the information is displayed on a single

plane.e.g. LED , LCD

Non-Planar display devicesCharacters are displayed in

different planes.e.g. nixie tube display

Display devices

Analog display devices (cathode-ray tubes)• Oscilloscope tubes• TV CRTs

Digital display devices• LED displays • LCD (liquid crystal)

displays• Dot-Matrix display

A Nixie tube, or cold cathode display, is an electronic device for displaying numerals or other information using glow discharge.

Inside the nixie tubeThe glass tube contains a wire-mesh anode and multiple cathodes, shaped like numerals or other symbols. Applying power to one cathode surrounds it with an orange glow discharge. The tube is filled with a gas at low pressure, usually mostly neon and often a little mercury or argon, in a Penning mixture.

Although it resembles a vacuum tube in appearance, its operation does not depend on thermionic emission of electrons from a heated cathode. It is therefore called a cold-cathode tube (a form of gas-filled tube), or a variant of neon lamp. Such tubes rarely exceed 40 °C (104 °F) even under the most severe of operating conditions in a room at ambient temperature.

LCD displaysA liquid-crystal display (LCD) is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals. Liquid crystals do not emit light directly.

LCD displays

Dynamic Scattering Field Scattering

Dynamic Scattering LCD displays

Dynamic scattering LCD displays consist of a thin Liquid Crystal layer sandwiched between two layers of glass. These glass pieces have a transparent conducting coating. Whenever a potential is applied at the conductive coatings the liquid crystal molecules start moving randomly causing turbulence. This turbulence causes the scattering of light which comes out of the glass layer or is reflected back by mirrors. So required patterns could be obtained by etching away the conductive layer by acid or by applying photoresist.

Two thin polarizing optical filters are placed at the inside of each glass sheet. The LCD material is of twisted nematic type which twists the light passing through the cell when the latter is not energized. This allows light to pass through the optical filters and the cell appears bright. When the cell is energized no twisting of light takes place and the cell appears dull.

Field Scattering LCD displays

Dot matrix display In a dot matrix display, multiple LEDs are wired together in rows and columns. This is done to minimize the number of pins required to drive them. For example, a 8×8 matrix of LEDs (shown below) would need 64 I/O pins, one for each LED pixel. By wiring all the anodes together in rows (R1 through R8), and cathodes in columns (C1 through C8), the required number of I/O pins is reduced to 16. Each LED is addressed by its row and column number. In the figure below, if R4 is pulled high and C3 is pulled low, the LED in fourth row and third column will be turned on. Characters can be displayed by fast scanning of either rows or columns.

Seven Segment displays A seven-segment display (SSD), 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. Individually on or off, they can be combined to produce simplified representations of the Arabic numerals. 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. There are also fourteen-segment displays and sixteen-segment displays (for full alphanumeric).

The displays common pin is generally used to identify which type of 7-segment display it is. As each LED has two connecting pins, one called the “Anode” and the other called the “Cathode”, there are therefore two types of LED 7-segment display called: Common Cathode (CC) and Common Anode (CA).

The difference between the two displays, as their name suggests, is that the common cathode has all the cathodes of the 7-segments connected directly together and the common anode has all the anodes of the 7-segments connected together and is illuminated as follows.

Common Cathode Common Anode

The Common Cathode (CC) – In the common cathode display, all the cathode connections of the LED segments are joined together to logic “0” or ground. The individual segments are illuminated by application of a “HIGH”, or logic “1” signal via a current limiting resistor to forward bias the individual Anode terminals (a-g).

Common Anode:In general, common anode displays are more popular as many logic circuits can sink more current than they can source. Depending upon the decimal digit to be displayed, the particular set of LEDs is forward biased. For instance, to display the numerical digit 0, we will need to light up six of the LED segments corresponding to a, b, c, d, e and f. Then the various digits from 0 through 9 can be displayed using a 7-segment display as shown.

Data Loggers

Data Loggers A data logger an electronic instrument that records measurements at set intervals over a period of time. Depending on the particular data logger, such measurements can include: air temperature, relative humidity, AC/DC current and voltage, differential pressure, time-of-use (lights, motors, etc.), light intensity, water temperature, water level, dissolved oxygen, soil moisture, rainfall, wind speed and direction, leaf wetness, pulse signals, room occupancy, plug load, and many more.

Data loggers are typically compact, battery-powered devices equipped with an internal microprocessor, data storage, and one or more sensors. They can be deployed indoors, outdoors, and underwater, and can record data for up to months at a time, unattended. A data logger may be a single-unit, stand-alone device with internal sensors, which fits in the palm of a hand, or it may be a multi-channel data collection instrument equipped with one or more external sensors.

Where are data loggers used?

Data loggers are used in a broad range of indoor, outdoor and underwater environments – essentially anywhere data is needed and the convenience of battery power is preferred.

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