Introduction:-
Multipurpose digital display unit is an ARM7 Lpc2148 processor based project, which provides ease of communication between administration and students in colleges.
Whenever a notice is passed it can be directly displayed on the Digital notice board, without efforts like printing on a paper and then attaching it manually to the notice board. Many of the students don’t have a habit of continuously check and read the notice board. But using digital notice board we can directly display it on a big LED display board, which can be easily seen and read by many students at a time.
Hence most of the students can quickly come to know what is the notice and the important message is conveyed to all. The notice keeps on rolling over and over.
The ARM7 controller core. Core is the key component of many successful 32 bit embedded systems. ARM cores are widely used in mobile phones handled organizers and multitude of other portable devices. Arm’s designers have come a long way from the first ARM1 prototype in 1985.
Objectives and Scope of work
To provide fastest medium that notifies and conveys important notices and messages, from administration to students within colleges and in bigger organizations. All with the only effort of typing and displaying.
This project can be widely used in colleges, organizations and in Government offices to notify student, employees and people. In future with more modifications such as the use of Bluetooth, use of graphics LED display, use of internet to directly display a webpage, etc.
Problem Definition:-
In Multipurpose Digital Display Unit we have to use a 16x96 led matrix display board that displays the message we type using a 4x4 aplhanumeric keypad.
We need an ARM7 Kit interfaced with a display and a keypad, along with an SPI memory to store the message entered through the keypad.
We also need temperature sensor, pressure and humidity sensor, to sense the respective parameters and a real time clock to keep running real time. These sensors are interfaced with the ARM7 processor and values of respective parameters at that time are displayed.
Following block diagram shows different blocks involved in Multipurpose digital display unit.
ARM LPC2148
Features
- 16/32-bit ARM7TDMI-S microcontroller in a tiny LQFP64 package
- 8 to 40 kB of on-chip static RAM and 32 to 512 kB of on-chip flash program memory.
128 bit wide interface/accelerator enables high speed 60 MHz operation.
- In-System/In-Application Programming (ISP/IAP) via on-chip boot-loader software.
Single flash sector or full chip erase in 400 ms and programming of 256 bytes in 1ms.
- Single 10-bit D/A converter provides variable analog output.
- Two 32-bit timers/external event counters (with four capture and four compare channels each), PWM unit (six outputs) and watchdog.
- Low power real-time clock with independent power and dedicated 32 kHz clock input.
- Single power supply chip with Power-On Reset (POR) and BOD circuits:– CPU operating voltage range of 3.0 V to 3.6 V (3.3 V ± 10 %) with 5 V tolerant I/O pads
- Processor wake-up from Power-down mode via external interrupt, USB, Brown-Out
Detect (BOD) or Real-Time Clock (RTC).
- Up to 45 of 5 V tolerant fast general purpose I/O pins in a tiny LQFP64 package.
Software requirements:-
- Keil uvision compiler(ARM)
- Embedded c
- Express PCB
- Flash Magic
- Adobe reader (to view manuals and datasheets)
Hardware requirements:-
- LPC2148
- 16x96 LED Matrix display
- 4x4 Matrix alphanumeric keypad
TECHNOLOGY
An LED will begin to emit light when more than 2 or 3 volts is applied to it. Some external system must control the current through the LED to prevent destruction by overheating. The LED consists of a chip of semiconducting material doped with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers electrons and holes flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level and releases energy in the form of a photon.
The wavelength of the light emitted, and thus its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes usually recombine by a non-radiative transition, which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible, or near-ultraviolet light.
LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have enabled making devices with ever-shorter wavelengths, emitting light in a variety of colors.LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.
Most materials used for LED production have very high refractive indices. This means that much light will be reflected back into the material at the material/air surface interface. Thus, light extraction in LEDs is an important aspect of LED production, subject to much research and development. LED performance is temperature dependent. Most manufacturers' published ratings of LEDs are for an operating temperature of 25 °C (77 °F). LEDs used outdoors,
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such as traffic signals or in-pavement signal lights, and that are utilized in climates where the temperature within the light fixture gets very high, could result in low signal intensities or even failure. LED light output rises at lower temperatures, leveling off, depending on type, at around −30 °C (−22 °F Thus, LED technology may be a good replacement in uses such as supermarket freezer lighting and will last longer than other technologies. Because LEDs emit less heat than incandescent bulbs, they are an energy-efficient technology for uses such as in freezers and refrigerators. However, because they emit little heat, ice and snow may build up on the LED light fixture in colder climates. Similarly, this lack of waste heat generation has been observed to sometimes cause significant problems with street traffic signals and airport runway lighting in snow-prone areas. In response to this problem, some LED lighting systems have been designed with an added heating circuit at the expense of reduced overall electrical efficiency of the system; additionally, research has been done to develop heat sink technologies that will transfer heat produced within the junction to appropriate areas of the light fixture.
3.5.2 ADVANTAGES
- Efficiency: LEDs emit more lumens per watt than incandescent light bulbs. The efficiency of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes.
- Color: LEDs can emit light of an intended color without using any color filters as traditional lighting methods need. This is more efficient and can lower initial costs.
- Size: LEDs can be very small (smaller than 2 mm2) and are easily attached to printed circuit boards.
- On/Off time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond. LEDs used in communications devices can have even faster response times.
- Cycling: LEDs are ideal for uses subject to frequent on-off cycling, unlike incandescent and fluorescent lamps that fail faster when cycled often, or High-intensity discharge lamps (HID lamps) that require a long time before restarting.
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- Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering the forward current. This pulse-width modulation is why LED lights, particularly headlights on cars, when viewed on camera or by some people, appear to be flashing or flickering. This is a type of stroboscopic effect.
- Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED.
- Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs.
- Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. Fluorescent tubes typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000 to 2,000 hours. Several DOE demonstrations have shown that reduced maintenance costs from this extended lifetime, rather than energy savings, is the primary factor in determining the payback period for an LED product.
- Shock resistance: LEDs, being solid-state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs, which are fragile.
- Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner. For larger LED packages total internal reflection (TIR) lenses are often used to the same effect. However, when large quantities of light are needed many light sources are usually deployed, which are difficult to focus or collimate towards the same target.
3.5.3 DISADVANTAGES
- High initial price: LEDs are currently more expensive, price per lumen, on an initial capital cost basis, than most conventional lighting technologies. As of 2012, the cost per thousand lumens (kilolumen) was about $6. The price was expected to reach $2/kilolumen by 2013. At least one manufacturer claims to have reached $1 per kilolumen as of March 2014. The additional expense
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partially stems from the relatively low lumen output and the drive circuitry and power supplies needed.
- Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment – or "thermal management" properties. Over-driving an LED in high ambient temperatures may result in overheating the LED package, eventually leading to device failure. An adequate heat sink is needed to maintain long life. This is especially important in automotive, medical, and military uses where devices must operate over a wide range of temperatures, which require low failure rates. Toshiba has produced LEDs with an operating temperature range of -40 to 100 °C, which suits the LEDs for both indoor and outdoor use in applications such as lamps, ceiling lighting, street lights, and floodlights.
- Voltage sensitivity: LEDs must be supplied with the voltage above the threshold and a current below the rating. Current and lifetime change greatly with small change in applied voltage. They thus require a current-regulated supply (usually just a series resistor for indicator LEDs)
- Light quality: Most cool-white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under cool-white LED illumination than sunlight or incandescent sources, due to metamerism red surfaces being rendered particularly badly by typical phosphor-based cool-white LEDs. However, the color-rendering properties of common fluorescent lamps are often inferior to what is now available in state-of-art white LEDs.
- Area light source: Single LEDs do not approximate a point source of light giving a spherical light distribution, but rather a lambertian distribution. So LEDs are difficult to apply to uses needing a spherical light field; however, different fields of light can be manipulated by the application of different optics or "lenses". LEDs cannot provide divergence below a few degrees. In contrast, lasers can emit beams with divergences of 0.2 degrees or less.
- Electrical polarity: Unlike incandescent light bulbs, which illuminate regardless of the electrical polarity, LEDs will only light with correct electrical polarity. To automatically match source polarity to LED devices, rectifiers can be used.
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- Blue hazard: There is a concern that blue LEDs and cool-white LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1–05: Recommended Practice for Ph0tobiological Safety for Lamp and Lamp Systems.
- Blue pollution: Because cool-white LEDs with high color temperature emit proportionally more blue light than conventional outdoor light sources such as high-pressure sodium vapor lamps, the strong wavelength dependence of Rayleigh scattering means that cool-white LEDs can cause more light pollution than other light sources. The International Dark-Sky Association discourages using white light sources with correlated color temperature above 3,000 K.
- Efficiency droop: The luminous efficacy of LEDs decreases as the electrical current increases. Heating also increases with higher currents which compromises the lifetime of the LED. These effects put practical limits on the current through an LED in high power applications.
- Impact on insects: LEDs are much more attractive to insects than sodium-vapor lights, so much so that there has been speculative concern about the possibility of disruption to food webs.
APPLICATIONS
LED uses fall into four major categories:
- Visual signals where light goes more or less directly from the source to the human eye, to convey a message or meaning.
- Illumination where light is reflected from objects to give visual response of these objects.
- Measuring and interacting with processes involving no human vision.
- Narrow band light sensors where LEDs operate in a reverse-bias mode and respond to incident light, instead of emitting light. See LEDs as light sensors.
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