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Introduction Propeller clock was first made by Bob Blick. In this project, our aim is to use 89S52 microprocessor to control a row of LEDs to display some images and function it as a clock. In display , the lights, LEDs, or what ever makes visible dots are not on all the time. The leds turn on and off, one after another, very rapidly. Due to the slow response of the human e ye, we get the impression that the lights are on all together and we can read the display. Scanning in this clock is mechanically. A limited number of le ds are placed in a row and attached to a rotating board. The l eds are turned on and off at very precise times and places. Th is gives the impression that there are several leds making up a complete display. All we can see are the lighted dots from t he leds making a readable display that seems to float. Several sensors including infrared proximity sensors are used to detect the completion of one revolution. It can be used in place of various LCD displays when packaged in a proper way thereby leading to a cheaper way.
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Page 1: Propeller Clock

Introduction

Propeller clock was first made by Bob Blick.

In this project, our aim is to use 89S52 microprocessor to control a row of LEDs to display

some images and function it as a clock.

In display , the lights, LEDs, or what ever makes visible dots, are not on all the time. The leds

turn on and off, one after another, very rapidly. Due to the slow response of the human eye, w

e get the impression that the lights are on all together and we can read the display.

Scanning in this clock is mechanically. A limited number of leds are placed in a row and attac

hed to a rotating board. The leds are turned on and off at very precise times and places. This g

ives the impression that there are several leds making up a complete display. All we can see

are the lighted dots from the leds making a readable display that seems to float.

Several sensors including infrared proximity sensors are used to detect the completion of one

revolution.

It can be used in place of various LCD displays when packaged in a proper way thereby

leading to a cheaper way.

Page 2: Propeller Clock

Block Diagram

Power Supply Circuit

DC motor

Microcontrolled LEDs

Page 3: Propeller Clock

Principle

If you move a bright light fast by the eyes, it will leave a line behind because the human brain

and eyes are slow to interpret fast changes in light intensity, leaving an afterglow.

If a row of LED’s is moved sideways while the LED’s intensity is changed, an image will

shortly visualize in the air where the LED’s are moved. If this is done several times, for

example if the LED’s are mounted on the end of a bar mounted on a motor as in the figure on

the right, the same area in the air could be scanned several times showing the same image

each time. Done at high speed it would generate a quite good virtual display hanging in air

thanks to the persistence of vision effect of the brain. People has started to refer to this kind

of display as POV-displays (Persistence of vision displays) as if it was the only type of

displays depending on the persistence of vision effect but that is kind of ignorant as many

display types use the same effect, like for example CRTs and multiplexed LED displays, thus

"mechanically scanned display" is a more accurate name.

Page 4: Propeller Clock

How this clock works:

The basic principle used is the persistence of vision. As the LEDs rotate at a high speed they

can be controlled with the help of a micro-controller so as to glow them in such a

combination that a floating display is formed.

A motor spins the "propeller", and a small microprocessor keeps track of time and changes

the pattern on seven LEDs with exact timing to simulate an array of LEDs. It is an illusion,

but it works nicely.

Page 5: Propeller Clock

Display Formation

As we have already learned that POV is the basic phenonmemn involved, now to use this we

need to get into some details.

We first divide our numbers into matrix of 4*6.

If 2 is to be displayed then :

This how a no. would appear.

On the basis of the ABOVE diagram , coding is done and then the display is formed.

Page 6: Propeller Clock

Circuit Diagram

Page 7: Propeller Clock

Components list

COMPONENT NAME SPECIFICATION QUANTITY

Microcontroller AT89S52 1

10k Carbon film Resistor 2

1k Carbon film Resistor 1

10uf Electrolytic Capacitor 1

10k Resistance array SIP 1

220ohm Carbon film Resistor 9

LEDS Red Color 8

Crystal 11.095/12 Mhz 1

IC base 40 pin 1

.01uf Disk capacitor(104) 1

IC 7805 Regualtor 1

9v Transformer 1

1n4007 Diodes 4

1000uf Electrolytic Capcitor 1

DC motor High Speed 1

Page 8: Propeller Clock

LED

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator

lamps in many devices, and are increasingly used for lighting. Introduced as a practical

electronic component in 1962,[2] early LEDs emitted low-intensity red light, but modern

versions are available across the visible, ultraviolet and infrared wavelengths, with very high

brightness.

The LED is based on the semiconductor diode. When a diode is forward biased (switched

on),electrons are able to recombine with holes within the device, releasing energy in the form

ofphotons. 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 usually small in area (less than 1 mm2), and integrated optical components are used to

shape its radiation pattern and assist in reflection.[3] LEDs present many advantages over

incandescent light sources including lower energy consumption, longer lifetime, improved

robustness, smaller size, faster switching, and greater durability and reliability. However,

they are relatively expensive and require more precise current and heat management than

traditional light sources. Current LED products for general lighting are more expensive to

buy than fluorescent lamp sources of comparable output.

They also enjoy use in applications as diverse as replacements for traditional light sources

inaviation lighting, automotive lighting (particularly indicators) and in traffic signals. The

compact size of LEDs has allowed new text and video displays and sensors to be developed,

while their high switching rates are useful in advanced communications technology. IR LEDs

are also used in many commercial products such as a TV remote.

Page 9: Propeller Clock

PCB Layout

Page 10: Propeller Clock

Software Coding

#include<REG52.H>

#define port0 P0

#define port1 P1

#define port2 P2

#define port3 P3

char digit[10][5]={{0x00,0x70,0x88,0x70,0x00},

{0x00,0x00,0xF8,0x00,0x00},

{0x48,0x18,0xA8,0x48,0x00},

{0x00,0x88,0xA8,0x50,0x00},

{0x00,0xE0,0x20,0xF8,0x00},

{0x00,0xE8,0xA8,0xB8,0x00},

{0x00,0x70,0xA8,0x30,0x00},

{0x08,0x90,0xA0,0xC0,0x00},

{0x00,0x50,0xA8,0x50,0x00},

{0x00,0x40,0xA0,0xF8,0x00}};

unsigned int count=0;

int flag=0;

unsigned int sec1=0,sec2=0,min1=0,min2=0;

void timer0(void) interrupt 1

{ count++;

TH0=0x00;

TL0=0x00;

if (count==14)

{

Page 11: Propeller Clock

flag=1;

count=0;

}

}

void inc_seg()

{

sec1++;

if (sec1==10)

{

sec1=0;

sec2++;

}

if (sec2==6)

{

sec2=0;

min1++;

}

if (min1==10)

{

min2++;

min1=0;

}

if (min2==6)

{

min2=0;

}

}

Page 12: Propeller Clock

void delay1()//125

{

int i;

for (i=0;i<60;i++)

{

}

}

void delay4()

{

int i;

for (i=0;i<60;i++)

{

}

}

void delay2()

{

int i;

for (i=0;i<500;i++)

{

}

}

void delay3()

{

int i;

for (i=0;i<2300;i++)

{

}

Page 13: Propeller Clock

}

void disp_digit(int i)

{

int j;

for (j=1;j<=5;j++)

{

port0=~digit[i-1][j-1];

delay1();

port0=0xFF;

delay4();

}

}

void main(void)

{

port1=0x00;

port0=0x00;

port2=0x00;

port3=0x00;

TMOD=0x01;

TH0=0x00;

TL0=0x00;

TR0=1;

IE=0x82;

while (1)

{

if (flag==1)

{

Page 14: Propeller Clock

inc_seg();

flag=0;

}

disp_digit(min2);

port0=0xFF;

delay2();

disp_digit(min1);

port0=0xFF;

delay2();

disp_digit(sec2);

port0=0xFF;

delay2();

disp_digit(sec1);

port0=0xFF;

delay2();

delay3();

}

}

Page 15: Propeller Clock

Problems Faced and Troubleshooting

1. Balancing the PCB plate over the motor took a lot of our time.

2. RPM of the DC motor were not stable so the display is not always stable too.

3. To solve the RPM problem a regulator was used so as to vary the speed of the motor.

Page 16: Propeller Clock

Applications

1. It can be used to replace various public LCD screens thereby providing a cheaper

solution.

2. It can also be used as a stopwatch.

Future Scope

Once developed at a large scale and used with multicolor LEDs can be used to replace

LCD screen.

Page 17: Propeller Clock

Conclusion

This project explains about a basic principle of persistence of vision usingsimple low cost

circuit.

This can be used in large scale to form a nice display screens..

Page 18: Propeller Clock

References

Books:

Mohammed Ali Mazidi

Websites

1. www.logicbrigade.com

2. www.8051projects.net