Transcript Wiring a LED

Wiring a LED
Prototyping
What is a Light Emitting
Diode?
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The phenomenon of electroluminescence was first observed in
a piece of Silicon Carbide (SiC), in 1907 by Henry Joseph
Round.
The yellow light emitted by it was too dim to be of practical
use and difficulties in working with Silicon Carbide meant that
research was abandoned.
Further experiments were carried out in Germany in the late
1920s by Bernhard Gudden and Robert Wichard Pohl, using
phosphor materials made from Zinc Sulphide doped with
Copper (ZnS:Cu), although once again, the low level of light
produced meant that no in depth research was carried out.
In 1936 George Destriau published a report on the emission of
light by Zinc Sulphide (ZnS) powders, following the application
of an electric current and is widely credited with having
invented the term "electroluminescence".
History of the LED
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British experiments into electroluminescence, using the
semiconductor Gallium Arsenide (GaAs) in the 1950s led
to the first "modern" Light Emitting Diode (LED), which
appeared in the early 1960s.
It is said that early experimental laboratory LEDs
needed to sit in liquid nitrogen while operating and
considerable effort was required to make the
breakthroughs needed to create devices that would
function efficiently at room temperature.
The first commercial LEDs were only able to produce
invisible, infra red light, but still quickly found their way
into sensing and photo-electric applications.
History of the LED
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The first visible (red) light LEDs were
produced in the late 1960s, using
Gallium Arsenide Phosphide (GaAsP) on
a GaAs substrate.
Changing to a Gallium Phosphide (GaP)
substrate led to an increase in
efficiency, making for brighter red LEDs
and allowing the color orange to be
produced.
History of the LED
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By the mid 1970's Gallium Phosphide (GaP)
was itself being used as the light emitter and
was soon producing a pale green light. LEDs
using dual GaP chips (one in red and one in
green) were able to emit yellow light.
Yellow LEDs were also made in Russia using
Silicon Carbide at around this time, although
they were very inefficient compared to their
Western counterparts, which were producing
purer green light by the end of the decade.
History of the LED
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The use of Gallium Aluminum Arsenide
Phosphide (GaAlAsP) LEDs in the early
to mid 1980s brought the first
generation of superbright LEDs, first in
red, then yellow and finally green.
By the early 1990's ultrabright LEDs
using Indium Gallium Aluminum
Phosphide (InGaAlP) to produce
orange-red, orange, yellow and green
light had become available.
History of the LED
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The first significant blue LEDs also appeared at
the start of the 1990's, once again using
Silicon Carbide - a throwback to the earliest
semiconductor light sources, although like
their yellow Russian ancestors the light output
was very dim by today's standards.
Ultrabright blue Gallium Nitride (GaN) LEDs
arrived in the mid 1990s, with Indium Gallium
Nitride (InGaN) LEDs producing high-intensity
green and blue shortly thereafter.
History of the LED
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The ultrabright blue chips became the basis of
white LEDs, in which the light emitting chip is
coated with fluorescent phosphors.
These phosphors absorb the blue light from
the chip and then re-emit it as white light.
This same technique has been used to produce
virtually any color of visible light and today
there are LEDs on the market which can
produce previously "exotic" colors, such as
aqua and pink.
History of the LED
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Scientifically minded readers may have
realized by now that the history of LEDs has
been a long, slow "crawl up the spectrum",
starting with infra-red.
Indeed, the most recently developed LEDs emit
not just pure violet, but genuine ultra-violet
"black" light.
How much further up the light spectrum LEDs
can "go" is a matter of speculation, but who
knows ? it may one day even be possible to
produce LEDs which emit X-rays.
History of the LED
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However, the story of LEDs has not just been
about color, but brightness too.
Like computers, LEDs are becoming roughly
twice as powerful (bright) around every
eighteen months.
Early LEDs were only bright enough to be used
as indicators, or in the displays of early
calculators and digital watches.
More recently they have been starting to
appear in higher brightness applications and
will continue to do so for some time to come.
History of the LED
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For instance: all American traffic signals will have been
replaced with LEDs by late 2005;
the automotive industry has sworn to banish all
incandescent bulbs from cars by the end of the decade,
replacing them with LEDs - even in headlights.
Most of the large video screens seen at outdoor events
use many thousands of LEDs to produce video pictures.
Very soon, LEDs will be bright enough to light our
homes, offices and even our streets as well.
The extreme energy efficiency of LEDs means that solar
charged batteries can power LED units by night,
bringing light to the Third World and other areas with no
mains electricity.
Parts of an LED
How is a LED wired?
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How is an LED wired?
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LEDs must be connected the correct way,
the diagram may be labeled a or + for anode and k
or - for cathode (yes, it really is k, not c, for
cathode!).
The cathode is the short lead and there may be a
slight flat on the body of round LEDs.
LEDs can be damaged by heat when soldering, but
the risk is small unless you are very slow.
No special precautions are needed for soldering most
LEDs.
Defining the circuit
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Ohm's Law – Current = Voltage/Resistance
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One ohm is the resistance value through which one volt will maintain a current
of one ampere.
( I ) Current is what flows on a wire or conductor like water flowing
down a river. Current flows from points of high voltage to points of
low voltage on the surface of a conductor. Current is measured in (A)
amperes or amps.
( E ) Voltage is the difference in electrical potential between two
points in a circuit. It's the push or pressure behind current flow
through a circuit, and is measured in (V) volts.
( R ) Resistance determines how much current will flow through a
component. Resistors are used to control voltage and current levels. A
very high resistance allows a small amount of current to flow. A very
low resistance allows a large amount of current to flow. Resistance is
measured in ohms.
Forward Voltage
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Diode forward voltage
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If you have good specs from your supplier, you'll
want to enter the typical forward voltage here.
Ideally you'll have something that looks like "3.3V
@ 20 mA" which defines forward voltage and
current at one point on the operating curve. If you
don't have good specs, here's a table to help you
make decent guesses:
Forward voltage can also be remembered as the
required voltage needed for the LED to light.
Forward Voltage by Color
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Color
voltage (Volts)
IR
1.5
Red
2.0
Orange
2.0
Yellow
2.1
Green
2.2
true green
3.3
Blue
3.3
White
3.3
UV
3.3
blue
4.6
Superbright
5.0
Circuit
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Ohm's Law –
Current = Voltage/Resistance
(I = E/R)
Desk lamp specifications
Current = 20 ma
Forward Voltage = 3.4v DC
Resistance = Voltage X Current (E*I)
Answer = ? Ohm resistor
Soldering
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Follow the rules and regulations covered in
the teachers demonstration to solder the 180
ohm resistor to the cathode (-) lead on the
LED.
Then solder the LED to the Black and Red
wires on the Battery Cap. LED anode (+)
connects to the Red wire and the cathode (-)
connects to the Black wire.
Test your LED.