LED (or light emitting diode) is an optical diode that emits light energy in the form of a "photon" if it is forward biased.In electronics, we call this process of electroluminescence.The color of visible light emitted by the LED is in a range from blue to red and the determined spectral wavelength of the emitted light, which in turn depends on various impurities that are mixed into the semiconductor material during manufacture.
LEDs have many advantages compared to conventional lamps and luminaires, and perhaps the most important of these is their small size, durability, a variety of colors, low cost and easy availability, the ability to easily interact with various other electronic components in digital circuits.
But the main advantage of LEDs is that due to their small size, some of them may be concentrated in one compact housing, forming the so-called seven-segment display.
seven segment display consists of seven LEDs (hence its name) located rectangle, as shown.Each of the seven segment LED is called, since the illumination of the segment forms part numbers (decimal or hexadecimal 12 number system).Sometimes, within a single package is used 8th additional LED.It is used to display the decimal point (DP), thus allowing to display a decimal fraction, if two or more of the 7-segment displays are linked together to represent numbers more than ten.
Each of the seven segment LED display connected to a respective contact pad number, which is located directly on a rectangular plastic housing of the indicator.LED pins labeled tags from a to g, representing each segment.Other contacts LED segments are connected to each other and form a common conclusion.
So, forward bias is applied to the appropriate contacts LED segments in a specific order, make some segments light up, and the rest will remain blacked out, allowing you to highlight the desired character pattern number that is displayed on the display.This allows us to represent each of the ten decimal digits from 0 to 9 on the 7-segment display.
overall conclusion is usually used to determine the type of 7-segment display.Each LED display has two connection terminals, one of which is called the "anode" and the other, respectively, is called the "cathode".Therefore, seven-segment LED indicator can have two types of circuit performance - with a common cathode (OK) and common anode (OA).
difference between these two types of displays is that the design of the OC cathodes all 7 segments are directly connected with each other, and the common-(OA) is connected between the anode of anodes 7 segments.Both circuits operate as follows.
- common cathode (QA) - interconnected cathodes of all the LED segments has a logic "0" or connected to GND.The individual segments are displayed on the supply of the anode terminal of the signal "high" logic level or logic "1" through limiting resistor to create a forward bias of individual LEDs.
- common anode (OA) - to the anode of the LED segments are integrated and a logic level "1".The individual segments of the indicator light when each individual cathode connected to the ground, a logical "0" or low-grade signal through an appropriate current limiting resistor.
Overall seven segment displays with common anode more popular as many logic circuits may require more current than power supply capable of giving.Also note that the display common cathode is not a direct replacement circuit for a display with a common anode.And vice versa - is equivalent to integrating LEDs in the reverse direction, and thus the light emission does not occur.
Although the 7-segment display can be viewed as a single display, it still consists of seven individual LEDs in a single package, and as such, these LEDs need to be protected against overcurrent.LEDs emit light only when they are displaced in the forward direction, and the amount of light emitted is proportional to the direct current.It only means that the intensity of the LEDs increases approximately linearly with increasing current.So, to avoid damage to the LED, this direct current must be controlled and limited to a safe value of external limiting resistor.
These seven-segment LEDs are called static.A significant drawback is the large number of pins in the package.To overcome this limitation schemes apply dynamic management seven-segment displays.
seven segment display won great popularity among radio amateurs, because it is easy to use and easy to understand.
