Led Propeller Display - Engineering Seminar

Led Propeller Display
This paper explains the project which is a special kind of circular LED display. With the help some mechanical assembly,LED count, hardware requirement,and  hence overall cost is cut to very affordable price. It is made using the PIC 18F series microcontroller,this project use the principle of  Space  Multiplexing.This propeller display is mechanically scanned and displays the characters in digital format. This display consists of  8 monochrome  bright LEDs which are rotated to show the display.

Propeller is a term associated with a circular rotating object. As this project needs to rotate whole circuit assembly, there must be some prime mover attached to it. So, the term ‘Propeller’. This project using bright light emitting diodes for displaying the characters and symbols on its assembly. That’s whythis project is named as ‘PROPELLER LED DISPLAY. ‘ This is the phenomenon which is related to vision capability of human eye by which an afterimage is thought to persist for approximately 1/25 th of a second. So, if someone is observing the images at a rate of 25 images per second, then they appear to be continuous. The best example of this property is the red circle we observe when we rotate the firecracker or incense stick in circle. This project was started with a simple principle which is frequently encountered in our everyday life, 
which is Persistence of Vision. This phenomenon makes one feel fast moving/changing objects to appear continuous. A television is a common example; in which image is re-scanned every 25 times, thereby appear continuous. Further, a glowing objects if rotated in a circle at fast speed, it shows a continuous circle. By modifying this basic idea, 7 LEDs can be rotated in a circle, showing 7 concentric circles. But if these LEDs are switched at precise intervals, a steady display pattern can be shown. Existing systems do employ POV principle, but for displaying each pixel, individual LED is used. This results in a huge number of LEDs even for small sized displays. By using a propeller type display, LED count can be kept to a bare minimum. Even 7 LEDs can perform a task of over 525 LEDs.Applications can find their way into cost effective solutions for large public displays, information systems. It can directly replace Railway station information displays, bus stands and many more places.

Mechanical Assembly
Mechanical assembly plays a vital role in proper functioning of this project. The display is scanned each time, by rotating the whole assembly in a circular path. The basic idea we developed is on our own, by implementing and modifying different ways to do this. Following diagram shows the most reliable way, that we finally selected. Here, one major challenge was how to bring +5V supply to the spinning circuit. We tried the same by adopting twothree different methods, but finally concluded on the method, as shown in the figure. As seen in the diagram, one supply connection (GND) is provided through the motor’s shaft. Other terminal (Vcc) is connected, by arranging a friction disc-brush arrangement. The brush keeps its contact with the disc, so that current can be supplied. Most critical objective was to achieve pristine balance and overall good mechanical strength. For weight adjustment, we have provided one long screw, and weight can be attached or removed by adding / removing metallic bolts. If the assembly is balanced perfect, then it can achieve stability, and rotate at high RPMs too. This will improve the overall efficiency of this display.

Devices & Tools
PIC is a family of modified Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1650 originally developed by General Instrument's Microelectronics Division. The name PIC initially referred to "Peripheral Interface Controller".
PICs are popular with both industrial developers and hobbyists alike due to their low cost, wide availability, large user base, extensive collection of application notes, availability of low cost or free development tools, and serial programming (and re-programming with flash memory) capability. They are also commonly used in educational programming as they often come with the easy to use 'pic logicator' software.

2. LED’s
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other  lighting. Appearing as practical electronic components in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.
When a light-emitting diode is forward-biased (switched on), electrons are able torecombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compactfluorescent lamp sources of comparable output.
Light-emitting diodes are used in applications as diverse as aviation lighting, automotive lighting, advertising, general lighting, and traffic signals. LEDs have allowed new text, video displays, and sensors to be developed, while their high switching rates are also useful in advanced communications technology. Infrared LEDs are also used in the remote controlunits of many commercial products including televisions, DVD players, and other domestic appliances.

DC Motor used in this project is 12 V dc motor which is tested by using digital contact-less tachometer. Arrangement was made so that the sensing circuit gives high to low pulse for each completion of revolution. By measuring the time difference between two successive pulses RPS can be
calculated which further provide RPM value, as shown below: 
Power supply given to DC Motor = 9V
Time interval between two successive pulses as seen
CRO = 30.4ms
o RPS = 1 / (30.4ms)
o RPS = 33
o RPM= 33x60=1980

4. Shift registers
In digital circuits, a shift register is a cascade of flip flops, sharing the same clock, in which the output of each flip-flop is connected to the "data" input of the next flip-flop in the chain, resulting in a circuit that shifts by one position the "bit array" stored in it, shifting in the data present at its input and shifting out the last bit in the array, at each transition of the clock input. More generally, a shift registermay be multidimensional, such that its "data in" and stage outputs are themselves bit arrays: this is implemented simply by running several shift registers of the same bit-length in parallel.
Shift registers can have both parallel and serial inputs and outputs. These are often configured as serial-in, parallel-out (SIPO) or asparallel-in, serial-out (PISO). There are also types that have both serial and parallel input and types with serial and parallel output. There are also bi-directional shift registers which allow shifting in both directions: L→R or R→L. The serial input and last output of a shift register can also be connected to create a circular shift register.

It can be concluded that this paper is suitable for LED text display. There can be further upgradation in the paper which could lead to a much better system for led display. 

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