Week 13

DISPLAY  DOT MATRIX BOARD

Generally the LED Scrolled Message can be implemented with many different logics. Out of two are very famous is:

• LED moving message display board design using decade counters
• LED moving message display board design using shift registers

So I am implementing LED moving display using shift registers.LED Scrolling Display can be implemented by using any microcontroller like 8051, PIC and AVR controllers.

Before going for LED Dot Matrix, generally the LEDs are two types:

• High power LEDs
• Miniature LEDs

High power LEDs are very costly, so in this project we will use miniature type of LEDs. Basically the standard RED color LED requires 2-3V to ON. But to glow the LEDs brightly enough, it require 20mA current to flow.

To construct an array using 8 LEDs firstly the entire cathodes are connected together and should be grounded. Each LED anode is driven by manual switches or by microcontroller. The microcontroller is programmed to generate different patterns on these LEDs. The individual LED current is summed up and a large current flow into the ground terminal. If each LED takes 20mA current, therefore eight LEDs current = 8*20mA. A total of 160mA current sinks into the ground terminal.

By using single array of LEDs we can generate different type of patterns. If we arrange the LED arrays side by side with multiplexing technique, it is also possible to generate letters, symbols, numbers, pictures, animations also. The LED Dot Matrix can be constructed by connecting all the anode terminals of LED’s together in each row and all the cathode terminals are joined together in each column.

An 8x8 LED matrix construction is shown in figure below:

Common-row anode                                    common-row cathode