Scrolling message display board

To make an led ON/OFF we usually use one I/O pin of the microcontroller
this will work fine with 5 to 8 leds but when u have drive a display board
which may contain LEDs between 70 to 100 depending on the matrix size , using each microcontroller I/O to control each LED is impossible and !!!!!!!!

so there are ways in which we can control many leds using few i/o pins
1)using charlieplexing if we have n i/o pins we can control
n*(n-1) leds using this method and all the pattern's may not be possible in this case
more about charlieplexing can be found at charlieplexing

charlieplexing with 3 i/o pins



2)using Dot Matrix
leds a connected like this


two types common anode n common cathode type.....
u can buy this modules , they cost around Rs70(5*7 matrix)


here we send data row wise , that is activating one row at a time and through column we need to send the data which we want to see
this image might give a better idea


i have shown for two row's this repeat's in a loop for all the row ..

3) using decoder's this is the ultimate way and flickering can be seen if the microcontroller is working at slow speed's , we can control 1024 leds with 11 i/o pins two 5*32 decoder for row n column
we are not interested with this method , as modules are not available we need solder the whole LED network

Program which i have implemented
ATmega32 chip running @4mhz
compiler WINAVR

#include
#define F_CPU 4000000UL
#include
typedef unsigned char u8;
typedef unsigned int u16;

int main(void)
{
u16 data2[5]={1,2,4,8,16},y[5];
u16 i,j,k,p,t,l[5][6]={{0x7f,0x41,0x41,0x41,0x3e,0x00},{0x3e,0x41,0x41,0x41,0x3e,0x00},{0x7f,0x40,0x40,0x40,0x40,0x00},{0x7f,0x40,0x40,0x40,0x40,0x00},{0x01,0x02,0x7c,0x02,0x01,0x00}};//data to be displayed
DDRD=0X00; //control i/p for Lb and Rb
PORTD=0XFF; //internal pull ups
DDRA=0xff;//data O/p to dot matrix
DDRC=0xff; //control o/p to dot matrix
for(i=0;i<5;i++)
{
y[i]=0;
}

while(1)
{
for(i=0;i<5;i++)
{
for(p=0;p<6;p++)
{
// display data
for(j=0;j<50;j++)
{
for(k=0;k<5;k++)
{
PORTC=data2[4-k];
PORTA=y[k];

_delay_ms(1);

}
}
// next loop data
for(t=0;t<4;t++)
{
y[4-t]=y[3-t];
}

y[0]=l[i][p];//new data

}// end of p for

}// end of i for
}// end while

}

here's the vedio moving message vedio

PING PONG game on DOT matrix

charecter segmentation matlab

we will use the above image for processing

1.add the image to matlab work space

ch=imread('char.jpg');

2.convert the RGB image to gray scale using rgb2gray function
Gch=rgb2gray(ch);

3.convert this gray scale image to BW comparing with some threshold
bw= im2bw(Gch,graythresh(Gch));

now u will get a binary image containing 1 r 0 's which will be easy to process

4. find the edge's in that binary image
Ibw= edge(uint8(bw));
imshow(Ibw);

5.using Morphological process to enhance the image
se = strel('disk',4);
bw2 = imdilate(Ibw, se);
imshow(bw2);



6. filling the holes in the dilated image
fill= imfill(bw2,'holes');
imshow(fill)
7. labeling the parts of the image and marking their position
[lab n] = bwlabel(fill);
props = regionprops(lab);
Z = [props.BoundingBox];
Z= reshape(Z,[4 n]);


8. display the results
imshow(I);
hold on;
for i = 1:n
rectangle('position',z(:,i),'edgecolor','r');
end


this can be used with a neural network to recognize patterns
we will see how to do this in next blog