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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Transcript
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
Power Supply Circuit
DC motor
Microcontrolled LEDs
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.