hi,my name is zaheed, i would like to get details on moving message display (the circuit diagram and the c codes) using atmel 89c52

LED Message Scrolling Board with completed circuit diagram and the microcontroller programming. Sometimes this LED scrolling message board is referred as LED Message sign board or led scroller or digital signage. It is generally used to generate or display advertising signs, school sign, restaurant signs, custom street signs, simple led running text, digital sign, any outdoor signs, business signs, church signs, animated signs, gif text signs, any other informational signs, led banner, saftey signs, political signs, hand painted signs.

Generally the LED Scroller Message Generator can be implemented with many different logics. Two of them are very famous
1. LED moving message display board design using decade counters
2. LED moving message display board design using shift registers

The second one is very simple for a beginner. So in this post i am implementing LED moving display using shift registers.
LED Scrolling Display can be implemented by using any microcontroller like 8051, PIC, AVR, MSP430, and ARM based micro controllers. Here I implemented Scrolling Display by using 8051 microcontroller i.e., 89s52 microcontroller. some of the video below shows the led display working using AVR, ARM processor and MSP430 microcontroller. The next post will show the implementation by using PIC and AVR microcontrollers. So now we are going to implement the LED Message Scrolling board using 8051/8052 microcontroller (89c52 MCU).

CONSTRUCTION OF 8X8 LED DOT MATRIX:

Before going for LED Dot Matrix, let us first learn about how an LED should be drive. What value of resistance should be added in series for protection of the LED? here i am not going to explain about the led working or led construction, that would be a separate article in this blog. here i am going to explain how does led display works.
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.

LED DRIVING CIRCUIT (LED CIRCUIT):


The Figure 1.2 shows the how to drive an LED using 5v supply without any damage (led driver). If we connect directly the 5v supply to an LED, all the source current flow through LED and it will burn out the LED. So we need a resistor in series with LED as shown in the led circuit diagram. In electronics, load current always plays an important role to design a circuit. Here the load current is the current flowing through LED. Let us suppose, we need 20mA current to flow through the LED for better brightness, therefore the load current is 20mA and LED takes 2v to ON.

From ohms law
V = I * R
R = V/I
R = (5v-2v)/20mA
R = 150 ohms, but in the figure, I have used 200 ohms resistance. Don’t think about the 200 ohms, the correct one 150 ohms only. Because of my laziness I didn’t change that value.