The longer lead is the anode (+) and the shorter
lead is the cathode (&minus). In the schematic symbol for an LED (bottom),
the anode is on the left and the cathode is on the right. Light emitting diodes
are elements for light signalization in electronics.
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Fig LED
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They are manufactured in different shapes, colors and sizes. For
their low price, low consumption and simple use, they have almost completely
pushed aside other light sources- bulbs at first place.
It is important to
know that each diode will be immediately destroyed unless its current is
limited. This means that a conductor must be connected in parallel to a diode.
In order to correctly determine value of this conductor, it is necessary to
know diode’s voltage drop in forward direction, which depends on what material
a diode is made of and what colors it is. Values typical for the most
frequently used diodes are shown in table below: As seen, there are three main
types of LEDs. Standard ones
get full brightness at current of 20mA. Low
Current diodes get full brightness at ten time’s lower current while
Super Bright diodes produce
more intensive light than Standard ones.
Since the 8052 microcontrollers can
provide only low input current and since their pins are configured as outputs
when voltage level on them is equal to 0, direct confectioning to LEDs is
carried out as it is shown on figure (Low
current LED, cathode is connected to output pin).