Propeller Clock j5h56

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.

Block Diagram

Microcontrolled LEDs

DC motor

Power Supply Circuit

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.

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.

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.

Circuit Diagram

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

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.

PCB Layout

Software Coding #include

#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) { 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; } } 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++) { } } 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) { 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(); } }

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.

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.

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..

References

Books: Mohammed Ali Mazidi Websites 1. www.logicbrigade.com 2. www.8051projects.net