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Led Dot Matrix Moving Sign Problem

 
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hturluce



Joined: 12 Feb 2006
Posts: 2

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Led Dot Matrix Moving Sign Problem
PostPosted: Mon Feb 20, 2006 11:42 am     Reply with quote

Hello all,

I am a new member of this board, but follow posts since 2003.

I built an led moving message from a message I was following. It was:
http://www.ccsinfo.com/forum/viewtopic.php?t=21166&highlight=moving

The circuit was:


And here is the code:
Code:

#include <18F452.H>
#include <STDLIB.H>

#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, RESTART_WDT, ERRORS)

#define PIN_ST_CP     PIN_C2  // RCLK ----> Pin 12 ST_CP
#define PIN_SH_CP     PIN_C3  // SRCLK ---> Pin 11 SH_CP
#define PIN_SER_IN    PIN_C5  // SER -----> Pin 14
#define PIN_MRS       PIN_C1  // PIN 10
#define PIN_OE        PIN_C4  // PIN 13

#byte port_b = 0x0F81
#byte port_c = 0x0F82

#use fast_io(B)
#use fast_io(C)



long s1_char_size=41;
char s1[79];
long i;

void get_line1(void)
{
  for(i=0; i<s1_char_size; i++)
  {
    if(kbhit())
    {
      s1[i]=getc();
      delay_cycles(2);
      printf("%C",s1[i]);
      delay_us(1);
    }
    else
      i -= 1;
  }
}

char  const msg_default[] = "Yet onother moving message led board 123";

char  const ascii1[32][5] = {
   {0,0,0,0,0}                  //   0
   {0,0,95,0,0}         //   {0,95,0,0,0,0}
   //   1
   {0,7,0,7,0}          // {0, 7,0,7,0,0}
 //   2
   {20,127,20,127,20}          //   3
   {36, 42, 127, 42, 18}       //   4
   {39, 21, 107, 84, 114}      //   5
   {54, 73, 86, 32, 80}        //   6
   {0, 11, 7,0,0}      // {0, 11, 7,0,0,0}
//   7
   {0, 28, 34, 65,0}    // {0, 28, 34, 65,0,0}
 //   8
   {0, 65, 34, 28,0}    // {0, 65, 34, 28,0,0}
 //   9
   {42, 28, 127, 28, 42}       //   10
   {8, 8, 62, 8, 8}            //   11
   {0, 88, 56, 0,0}      // {0, 88, 56,0,0,0}
  //   12
   {8,8,8,8,8}                 //   13
   {0, 96, 96, 0,0}      // {0, 96, 96,0,0,0}
  //   14
   {32, 16, 8, 4, 2}           //   15
   {62, 81, 73, 69, 62}        //   16
   {0, 66, 127, 64,0}       // {0,66, 127, 64,0,0}
     //   17
   {114, 73, 73, 73, 70}       //   18
   {34, 65, 73, 73, 54}        //   19
   {24, 20, 18, 127, 16}       //   20
   {39, 69, 69, 69, 57}        //   21
   {60, 74, 73, 73, 48}        //   22
   {1, 113, 9, 5, 3}           //   23
   {54, 73, 73, 73, 54}        //   24
   {6, 73, 73, 41, 30}         //   25
   {0, 54,54,0,0}         // {0, 54, 54,0,0,0}
   //   26
   {0, 91, 59, 0,0}         // {0, 91, 59,0,0,0}     // 27
   {8, 20, 34, 65,0}           //   28
   {20, 20, 20, 20, 20}        //   29
   {65, 34, 20, 8,0}           //   30
   {2, 1, 81, 9, 6}            //   31
   };

char  const ascii2[32][5] = {
{50, 73, 121, 65, 62}          //      0
{124, 18, 17, 18, 124}         //      1   A
{65, 127, 73, 73, 54}          //      2   B
{62, 65, 65, 65, 34}           //      3   C
{65, 127, 65, 65, 62}          //      4   D
{127, 73, 73, 65, 65 }         //      5   E
{127, 9, 9, 1, 1}              //      6
{62, 65, 73, 73, 58}           //      7
{127, 8, 8, 8, 127}            //      8
{0, 65, 127, 65, 0}       // {0, 65, 127, 65,0,0}
        //      9
{32, 64, 65, 63, 1}            //      10
{127, 8, 20, 34, 65}           //      11
{127, 64, 64, 64, 64}          //      12
{127, 2, 12, 2, 127}           //      13
{127, 2,  4, 8, 127}           //      14
{62, 65, 65, 65, 62}           //      15
{127, 9, 9, 9, 6}              //      16
{62, 65, 81, 33, 94}           //      17
{127, 9, 25, 41, 70}           //      18
{38, 73, 73, 73, 50}           //      19
{1,1,127, 1, 1}                //      20
{63, 64, 64, 64, 63}           //      21
{7, 24, 96, 24, 7}             //      22
{127, 32, 24, 32, 127}         //      23
{99, 20, 8, 20, 99}            //      24
{3, 4, 120, 4, 3}              //      25
{97, 81, 73, 69, 67}           //      26
{0, 127, 65, 65,0}          // {0, 127, 65, 65,0,0}
          //      27
{2, 4, 8, 16, 32}              //      28
{0, 65, 65, 127,0}          // {0, 65, 65, 127,0,0}
          //      29
{4, 2, 1, 2, 4}                //      30
{64, 64, 64, 64, 64}           //      31
};

char  const ascii3[31][5] = {    // 0 -- 30 == 31 elements
   {0, 0, 7, 11,0}        // {0, 7, 11,0,0,0}
  //   0
   {32, 84, 84, 84, 56}     //   1
   {127, 40, 68, 68, 56}    //   2
   {56, 68, 68, 68,0}     //   3
   {56, 68, 68, 40, 127}     //   4
   {56, 84, 84, 84, 24}     //   5
   {8, 126, 9, 9, 2}     //   6
   {8, 84, 84, 84, 60}     //   7
   {127, 8, 4, 4, 120}     //   8
   {0, 68, 125, 64,0}      // {0, 68, 125, 64,0,0}
//   9
   {32, 64, 68, 61,0}     //   10
   {127, 16, 40, 68,0}     //   11
   {0, 65, 127, 64, 0}      // {0, 65, 127, 64,0,0}
//   12
   {124, 4, 120, 4, 120}     //   13
   {124, 8, 4, 4, 120}     //   14
   {56, 68, 68, 68, 56}     //   15
   {124, 20, 20, 20, 8}     //   16
   {8, 20, 20, 20, 124}     //   17
   {124, 8, 4, 4, 8}     //   18
   {72, 84, 84, 84, 36}     //   19
   {4, 63, 68, 68,0}     //   20
   {60, 64, 64, 32, 124}     //   21
   {28, 32, 64, 32, 28}     //   22
   {60, 64, 48, 64, 60}     //   23
   {68, 40, 16, 40, 68}     //   24
   {12,80, 80, 80, 60}     //   25
   {68, 100, 84, 76, 68}     //   26
   {0, 8, 54, 65,0}           // {0, 8, 54, 65,0,0}
//   27
   {0,0,119,0,0}             // {0, 119,0,0,0,0}     // 28
   {0, 65, 54, 8,0}           // {0, 65, 54, 8,0,0}
//   29
   {2,1,2,4,2}     //   30
};

void main(void)
{
  int char_index,i;
  int col_index;
//  int16 speed;
  int x = 0;
  long MSD, LSD;
  int delaycount;
  int16 startposition;

  set_tris_b(0);
  set_tris_c(0x40);
  set_tris_d(0);
  port_b = 0;
  port_c = 0;
  startposition = 0;
  delaycount=0;
      output_high(PIN_OE);
      output_low(PIN_MRS);

  for(i=0; i<79; i++)
    s1[i] = 16;

  for(i=0; i<sizeof(msg_default); i++)
    s1[i] = msg_default[i];

  delay_ms(100);
  do
  {
    if(!input(PIN_E1)) //if RE1==LOW (pressed)
    {
      do
      {
        delay_cycles(2);
        printf("\f\r\n");
        printf("\f\r\n How many char.(0--99):");
        MSD=getc();
        delay_cycles(2);
        printf("%C",MSD);
        delay_us(1);     
      }while(!isamoung(MSD,"0123456789"));
      do
      {
        LSD=getc();
        delay_cycles(2);
        printf("%C",LSD);
        delay_us(1);     
      }while(!isamoung(LSD,"0123456789"));

      s1_char_size = 10*(MSD-48) + (LSD-48);
      delay_cycles(2);
      printf("\r\n\n  Enter the %lu char.: ",s1_char_size);
      get_line1();      // acquire 16 char.
    }  // END of INPUT(PIN_E1)
    delaycount=4;
    while (delaycount)
    {
      col_index = startposition % 6;
      char_index = startposition / 6;

      if (char_index >= sizeof(s1))
      {
        startposition = 0;
        char_index = 0;
        col_index = 0;
      }
      x = s1[char_index];
      output_high(PIN_MRS);
      output_high(PIN_ST_CP);
      output_high(PIN_SH_CP);
      output_high(PIN_SER_IN);
      output_low(PIN_SH_CP);
      delay_us(1);
      output_high(PIN_SH_CP);
      output_low(PIN_SER_IN);

      for (i=0;i<60;i++) // we've 80 columns to
      {
        port_b=0;
        output_low(PIN_ST_CP);
        delay_us(1);
        output_high(PIN_ST_CP);
        delay_us(1);
        output_low(PIN_SH_CP);
        delay_us(1);
        output_high(PIN_SH_CP);
        if (col_index == 5)
        {
          col_index = 0;
          char_index++;
          if (char_index >= sizeof(s1))
            char_index = 0;
          x = s1[char_index];
        }       
        else
        {
          if ( x < 32)
            port_b = 0;
          else if( x < 64)     
            port_b = ascii1[x-32][col_index];
          else if( x < 96 )     
            port_b = ascii2[x-64][col_index];
          else if( x < 128)     
            port_b = ascii3[x-96][col_index];
          col_index++;
        }
        output_low(PIN_OE);
        delay_us(120);
        output_High(PIN_OE);
      }// END for-loop
      delaycount--;
    }
    startposition++;
//   
  } while(1);  //End of do-while
}// END main()


Test board working and scrolling left. Great, but there is an illusion when you watch the animation it looks like this:



if you look at the code you will find a line like;
Code:

delaycount=4;
    while (delaycount)
    {

this means, whole screen will be scanned 4 times to slow down the scrolling effect. And this scan makes this illusion. If you scan the screen only one time there won't be any problem. But this will make the effect faster which I don't want.

After that I tried to add a big delay to the end of the code, like:
Code:

    delay_ms(50);
    startposition++;

And not a suprise. Flickering.

I don't understand the problem. I tried couple of days and I gave up.

Please help me.


Regards.
hturluce



Joined: 12 Feb 2006
Posts: 2

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PostPosted: Tue Feb 21, 2006 9:14 am     Reply with quote

Anybody???
yerpa



Joined: 19 Feb 2004
Posts: 58
Location: Wisconsin

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PostPosted: Tue Feb 21, 2006 11:22 am     Reply with quote

I didn't read your code but I have built similar displays in the past, and I found out a couple of interesting things about human vision. Persistence of vision is in the multi-millisecond range, so your eye will hold an image for a little while after the LED is turned off. Therefore, you want to scan all of the rows as many times as you can before you advance the scroll position. Your eye will detect flicker for any scan frequency below about 70 scans per second. Make sure you don't advance the scroll position until an integer number of complete scans are done, or else part of the characters will appear dimmer than others.

On a side note, the characters on this kind of multiplexed displays will seem to lean to the left if you are scanning from top to bottom, and will appear to lean to the right if the scan is bottom-to-top. It is a pretty convincing illusion.

Of course, you will not be able to make a completely smooth scrolling effect because of the physical distance between dots. Be sure to observe the display from the actual viewing conditions, including the distance and any relative motion between the viewer and the display.

Nice schematic, what did you use to generate it?
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