What is LED matrix? Led matrix is a dot matrix of large display, low resolution value and is useful for both industrial or commercial displays as well as for hobbyist human interface machines. In contains a 2-D diode matrix which have the cathode joined in rows and anode in columns. In this LED matrix each can be control individually by controlling the electricity through each pair of columns or rows diodes. These matrix are very popular matrix by means of displaying information it, allows the static and animated images and text. A LED matrix is shown in figure.
Types of LED Matrix:
There are so many types are LED matric have been used for industrial and commercial purposes, some of which are discussing in this article with respect to structure.
- 8*8 dot Matrix
- 5*7 dot Matrix
- 128*16 Two lined
- 128*32 Four lined
- 128*64 Eight lined
8*8 dot Matrix:
In dot matrix multiple diodes are connecting together in rows and columns, this is done to minimize the number of pins required to drive the dot light emitting diodes. Suppose in 8*8 dot matrix there would be 64 I/O pins for displaying each
diode pixel. For making 8*8 dot matrix all the anodes are connecting together in rows R1 to R8, similarly the cathodes are connected together in columns C1 to C8, by doing this the required number of I/O pins have reduced by 16 shown is below:
According to the figure each LED is addressed to its row and column number. If R5 is pulled high and C4 pulled low, then the LED in fifth row and fourth column would be high, similarly the characteristics can also be displayed by scanning of each row and column.
5*7 dot Matrix:
A 5*7 LED matrix have 5 rows and 7 columns of light emitting dioses, which are connecting together for making this shown is figure in 3. According to the figure we want to display an alphabet word A then first we pulled high the column C1 and pulled low the other columns by blocking their ground paths. Now the C1 is pulled high and need to turn on the LEDs of rowsR2 to R7 of this column. This is done by the applying the forward bias voltage to these rows. Next select the column C2 and deselect the other column and apply the forward bias voltage across R1 and R5, and so on.
Construction of dot Matrix:
The construction of this display is very simple if you want to make your own prototype display then the diodes are just solder on Vero board or premade double or single sided board. Suppose we want a construct a prototype 8*8 dot matrix display shown in figure 2, then we have required 64 light emitting diodes. These diodes are solder on overboard or single sided board. The positive end of one diose is connected to other positive end of the diode for making the rows, similarly the 8 rows are made by connecting the positive end of each diode. The negative end one diode is connected to the negative end of other diode. For making the columns of this display, similarly the 8 columns are made by connecting the negative end of each diode. All these diodes are connected with each other through bare copper wire and all these are should be properly sold otherwise there would be no connection between all these.
Dot Matrix Interfacing with Microcontroller:
The dot matrix display consists of rows and columns, in these rows and columns LEDs are connecting. These can be on or off as wish, but this can be only done through microcontroller. Here we will interface pic microcontrollers with dot matrix display shown in figure.
According to the figure we can see that, the microcontroller each port pin can directly drive each row or column of dot matrix display. For driving the column lines of dot matrix display the microcontroller requires additional circuit. The AT89S51 microcontroller is a high performance, low power CMOS 8-bit microcontroller which have 4k byte programmable flash memory. This device was manufactured by using Atmel s high density nonvolatile memory technology. This is compatible with the industry standard 80C51instruction.This microcontroller consist of 4 ports and 32 I/O lines. Here the dot matrix display rows are connected of port 1 and columns are connected to port 2. But columns are connected with extra IC ULN2003A.This is a high voltage (50V) high current (500mA per channel) with Darlington pair transistor array. This IC have seven channels with individually clamp output diodes. This is an active high device this means that the logic high must be applied at the input side for making the cross ponding output high. The input pins are shown with 1B,2B,3B,4B,5B,6B and 7B while the cross ponding pins are shown with 1C,2C,3C,4C,5C,6C and 7C. For displaying the alphabet,A proper code is required, which is burn in microcontroller for turn on and turn off the cross pondingLED
Applications of LED Matrix Display:
LED matrix display is device used for displaying the information on machine, railway departure indicators, clocks and there are so many other devices which required a simple display of very low resolution. These displays are available in different resolutions. Here we explain the applications of 2-dimensional display used in different devices.
- Television Sets
- Computer Monitors
- Head Mounted Displays
- Broadcast Reference Monitors
- Medical Monitors.
The dot matrix display is used in home television sets for displaying the television viewing picture, channel view and loud speaker view.
In computer monitors the dot matrix display is used for displaying the data, picture and everything which is sending by the CPU.
Head Monitor Display:
The dot matrix display is used in head monitor display devices which are used in military, Government (fire, police etc.) civilian and commercial purposes.
Broadcast Reference Monitors:
It is used in broadcast reference monitor which are basically the video monitor that displays the different videos
It is used in that medical equipment which have the displaying facility for observing the disease conditions.
- It is more efficient because now it is capable of outputting 135 lumens/watt.
- It has long life almost 50,000 hours if properly installed.
- It is called solid state lighting because it is made of solid state material with no tube no filament of bulb to break.
- It is environmentally friendly because it has no mercury or any other hazardous material.
- Its brightness and colures can be easily controlled.
- It have no wash out colures like the other light sources such as fluorescents lights.
- It has low temperature even startup at zero temperature.
- Its price lumens per watt is currently more expensive as compared to the other conventional displays on the basis of capital cost
- Its performance totally depends upon design parameters so its design is little bit difficult for a good performance.
- When we are interfacing with microcontroller then required a good engineer writing the code because its code can’t have written every person.
- For operating the LED constant current and voltage are required every time sometime this become difficult.