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good afternoon, I am making a 7x10 led matrix in which I use a CD4017 to handle the 7 rows and 2 cascaded shift registers to handle the 10 columns. I first tried a programming to turn on my entire led matrix and it worked fine. Then, I tried to make a character appear statically and it worked fine. Next, I tried to make that character sweep from right to left and it worked fine. But, what I am having a hard time with is sweeping the message from right to left smoothly with a column of character to character spacing.

What I originally thought is that if I wanted to move a character from right to left, I have to shift the column values for all the rows by an appropriate amount (shift step) and once the character has been shifted enough, I start feeding the column values of the next character in the message for which, the formula that would create the right to left shift effect is: (current_char<scroll) | (next_char>>(8-shift_step)-scroll) But I don't get the expected result, the message scrolls from right to left but it doesn't do it with a column of separation between character and character and it doesn't do it in a fluid way either. In addition to that at the end of sweeping the message appears something strange that should not be there.

I recorded a video showing what I am saying: https://drive.google.com/file/d/1ebO5zassWY060mvWACPhcSLeOi5JmZAC/view

Code:

/*
 char_data is a two dimensional constant array that holds the 5-bit column values
 of individual rows for ASCII characters that are to be displayed on a 7x10 matrix. 
*/
const byte char_data[95][7]={
    {0, 0, 0, 0, 0, 0, 0}, // space
    {0b100, 0b100, 0b100, 0b100, 0b100, 0, 0b100}, // !
    {0b1010, 0b1010, 0b1010, 0, 0, 0, 0}, // "
    {0b1010, 0b1010, 0b11111, 0b1010, 0b11111, 0b1010, 0b1010}, // #
    {0b100, 0b1111, 0b10100, 0b1110, 0b101, 0b11110, 0b100}, // $
    {0b11000, 0b11001, 0b10, 0b100, 0b1000, 0b10011, 0b11}, // %
    {0b1000, 0b10100, 0b10100, 0b1000, 0b10101, 0b10010, 0b1101}, // &
    {0b100, 0b100, 0b100, 0, 0, 0, 0}, // '
    {0b100, 0b1000, 0b10000, 0b10000, 0b10000, 0b1000, 0b100}, // (
    {0b100, 0b10, 0b1, 0b1, 0b1, 0b10, 0b100}, // )
    {0b100, 0b10101, 0b1110, 0b100, 0b1110, 0b10101, 0b100}, // *
    {0, 0b100, 0b100, 0b11111, 0b100, 0b100, 0}, // +
    {0, 0, 0, 0, 0b100, 0b100, 0b1000}, // ,
    {0, 0, 0, 0b11111, 0, 0, 0}, // -
    {0, 0, 0, 0, 0, 0, 0b100}, // .
    {0, 0b1, 0b10, 0b100, 0b1000, 0b10000, 0}, // /
    {0b1110, 0b10001, 0b10011, 0b10101, 0b11001, 0b10001, 0b1110}, // 0
    {0b110, 0b1100, 0b100, 0b100, 0b100, 0b100, 0b1110}, // 1
    {0b1110, 0b10001, 0b1, 0b110, 0b1000, 0b10000, 0b11111}, // 2
    {0b11111, 0b1, 0b10, 0b110, 0b1, 0b10001, 0b1111}, // 3
    {0b10, 0b110, 0b1010, 0b10010, 0b11111, 0b10, 0b10}, // 4
    {0b11111, 0b10000, 0b11110, 0b1, 0b1, 0b10001, 0b1110}, // 5
    {0b01110, 0b10001, 0b10000, 0b11110, 0b10001, 0b10001, 0b1110}, // 6
    {0b11111, 0b1, 0b10, 0b100, 0b1000, 0b1000, 0b1000}, // 7
    {0b01110, 0b10001, 0b10001, 0b1110, 0b10001, 0b10001, 0b1110}, // 8
    {0b01110, 0b10001, 0b10001, 0b1111, 0b1, 0b10001, 0b1110}, // 9
    {0, 0, 0b100, 0, 0b100, 0, 0}, // :
    {0, 0, 0b100, 0, 0b100, 0b100, 0b1000}, // ;
    {0b10, 0b100, 0b1000, 0b10000, 0b1000, 0b100, 0b10}, // <
    {0, 0, 0b11111, 0, 0b11111, 0, 0}, // =
    {0b1000, 0b100, 0b10, 0b1, 0b10, 0b100, 0b1000}, // >
    {0b1110, 0b10001, 0b1, 0b10, 0b100, 0, 0b100}, // ?
    {0b1110, 0b10001, 0b10111, 0b10101, 0b10110, 0b10000, 0b1111}, // @
    {0b1110, 0b10001, 0b10001, 0b11111, 0b10001, 0b10001, 0b10001}, // A
    {0b11110, 0b10001, 0b10001, 0b11110, 0b10001, 0b10001, 0b11110}, // B
    {0b1110, 0b10001, 0b10000, 0b10000, 0b10000, 0b10001, 0b1110}, // C
    {0b11110, 0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b11110}, // D
    {0b11111, 0b10000, 0b10000, 0b11110, 0b10000, 0b10000, 0b11111}, // E
    {0b11111, 0b10000, 0b10000, 0b11110, 0b10000, 0b10000, 0b10000}, // F
    {0b1110, 0b10001, 0b10000, 0b10111, 0b10101, 0b10001, 0b1110}, // G
    {0b10001, 0b10001, 0b10001, 0b11111, 0b10001, 0b10001, 0b10001}, // H
    {0b11111, 0b100, 0b100, 0b100, 0b100, 0b100, 0b11111}, // I
    {0b1, 0b1, 0b1, 0b1, 0b1, 0b10001, 0b1110}, // J
    {0b10001, 0b10001, 0b10010, 0b11100, 0b10010, 0b10001, 0b10001}, // K
    {0b10000, 0b10000, 0b10000, 0b10000, 0b10000, 0b10000, 0b11111}, // L
    {0b10001, 0b11011, 0b10101, 0b10101, 0b10001, 0b10001, 0b10001}, // M
    {0b10001, 0b10001, 0b11001, 0b10101, 0b10011, 0b10001, 0b10001}, // N
    {0b1110, 0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b1110}, // O
    {0b11110, 0b10001, 0b10001, 0b11110, 0b10000, 0b10000, 0b10000}, // P
    {0b1110, 0b10001, 0b10001, 0b10001, 0b10101, 0b10011, 0b1111}, // Q
    {0b11110, 0b10001, 0b10001, 0b11110, 0b10001, 0b10001, 0b10001}, // R
    {0b1111, 0b10000, 0b10000, 0b1110, 0b1, 0b1, 0b11110}, // S
    {0b11111, 0b100, 0b100, 0b100, 0b100, 0b100, 0b100}, // T
    {0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b1110}, // U
    {0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b1010, 0b100}, // V
    {0b10001, 0b10001, 0b10001, 0b10101, 0b10101, 0b11011, 0b10001}, // W
    {0b10001, 0b10001, 0b1010, 0b100, 0b1010, 0b10001, 0b10001}, // X
    {0b10001, 0b10001, 0b1010, 0b100, 0b100, 0b100, 0b100}, // Y
    {0b11111, 0b1, 0b10, 0b100, 0b1000, 0b10000, 0b11111}, // Z
    {0b1110, 0b1000, 0b1000, 0b1000, 0b1000, 0b1000, 0b1110}, // [
    {0, 0b10000, 0b1000, 0b100, 0b10, 0b1, 0}, // backward slash
    {0b1110, 0b10, 0b10, 0b10, 0b10, 0b10, 0b1110}, // ]
    {0, 0, 0b100, 0b1010, 0b10001, 0, 0}, // ^
    {0, 0, 0, 0, 0, 0, 0b11111}, // _
    {0b1000, 0b100, 0b10, 0, 0, 0, 0}, // `
    {0, 0, 0b1110, 0b1, 0b1111, 0b10001, 0b1111}, // a
    {0b10000, 0b10000, 0b10000, 0b11110, 0b10001, 0b10001, 0b11110}, // b
    {0, 0, 0b1110, 0b10001, 0b10000, 0b10001, 0b1110}, // c
    {0b1, 0b1, 0b1, 0b1111, 0b10001, 0b10001, 0b1111}, // d
    {0, 0, 0b1110, 0b10001, 0b11111, 0b10000, 0b1111}, // e
    {0b1110, 0b1001, 0b11100, 0b1000, 0b1000, 0b1000, 0b1000}, // f
    {0, 0, 0b1110, 0b10001, 0b1111, 0b1, 0b1110}, // g
    {0b10000, 0b10000, 0b10000, 0b11110, 0b10001, 0b10001, 0b10001}, // h
    {0b100, 0, 0b100, 0b100, 0b100, 0b100, 0b1110}, // i
    {0b1, 0, 0b11, 0b1, 0b1, 0b10001, 0b1110}, // j
    {0b10000, 0b10000, 0b10001, 0b10010, 0b11100, 0b10010, 0b10001}, // k
    {0b1100, 0b100, 0b100, 0b100, 0b100, 0b100, 0b1110}, // l
    {0, 0, 0b11110, 0b10101, 0b10101, 0b10101, 0b10101}, // m
    {0, 0, 0b11110, 0b10001, 0b10001, 0b10001, 0b10001}, // n
    {0, 0, 0b1110, 0b10001, 0b10001, 0b10001, 0b1110}, // o
    {0, 0, 0b1111, 0b1001, 0b1110, 0b1000, 0b1000}, // p
    {0, 0, 0b1111, 0b10001, 0b1111, 0b1, 0b1}, // q
    {0, 0, 0b10111, 0b11000, 0b10000, 0b10000, 0b10000}, // r
    {0, 0, 0b1111, 0b10000, 0b1110, 0b1, 0b11110}, // s
    {0b100, 0b100, 0b1110, 0b100, 0b100, 0b100, 0b11}, // t
    {0, 0, 0b10001, 0b10001, 0b10001, 0b10011, 0b1101}, // u
    {0, 0, 0b10001, 0b10001, 0b10001, 0b1010, 0b100}, // v
    {0, 0, 0b10001, 0b10001, 0b10101, 0b11111, 0b10101}, // w
    {0, 0, 0b10001, 0b1010, 0b100, 0b1010, 0b10001}, // x
    {0, 0, 0b10001, 0b10001, 0b1111, 0b1, 0b11110}, // y
    {0, 0, 0b11111, 0b10, 0b100, 0b1000, 0b11111}, // z
    {0b10, 0b100, 0b100, 0b1000, 0b100, 0b100, 0b10}, // {
    {0b100, 0b100, 0b100, 0b100, 0b100, 0b100, 0b100}, // |
    {0b1000, 0b100, 0b100, 0b10, 0b100, 0b100, 0b1000}, // }
    {0, 0, 0, 0b1010, 0b10101, 0, 0} // ~
};
char message[] = "MATRIX LED 7X10 WITH ATMEGA328p";
int string_length = strlen(message);
byte shift_step = 1;

void setup(){
    // PORTB as output.
    // Pin 13: ClockRegister
    // Pin 12: Latch
    // Pin 11: Data
    // Pin 10: Reset
    // Pin 9: Clock4017
    DDRB = 0b111111;
    // Makes sure the 4017 value is 0.
    PORTB |= (1 << PB2);
    PORTB &= ~(1 << PB2);
    Serial.begin(9600);
}

void send_data(uint16_t data){
    uint16_t mask = 1, flag = 0;
    for (byte i=0; i<10; i++){
        flag = data & mask;
        if (flag) PORTB |= (1 << PB3);
        else PORTB &= ~(1 << PB3);
        PORTB |= (1 << PB5);
        PORTB &= ~(1 << PB5);
        mask <<= 1;
    }
    PORTB |= (1 << PB4);
    PORTB &= ~(1 << PB4);
}

void display_pattern(byte loops){
    for (byte c=0; c<string_length; c++){ // For each character
        for (byte scroll=0; scroll<10; scroll++){ // For each column.
            for (byte t=0; t<loops; t++){ // The delay we get with loops.
                for (byte z=0; z<7; z++){ // For each row.
                    // To obtain the position of the current character in the char_data array, subtract 32 from the ASCII value of the character itself.     
                    byte index = message[c];
                    byte temp = char_data[index-32][z];
                    byte index_2 = message[c+1];
                    byte temp_2 = char_data[index_2-32][z];
                    send_data((temp<<scroll) | (temp_2>>(8-shift_step)-scroll));
                    delayMicroseconds(800);
                    // Clear the row so we can go on to the next row without smearing.
                    send_data(0);
                    // On to the next row.
                    PORTB |= (1 << PB1);
                    PORTB &= ~(1 << PB1);
                }
                // Select the first row.
                PORTB |= (1 << PB2);
                PORTB &= ~(1 << PB2);
            }
        }
    }
}

void loop(){
    display_pattern(10);
    delay(100000);
}

I appreciate the help.

2
  • For the strange char at the end of the display, I think your index_2 is accessing beyond the strlen(message) toward the end of the message.
    – hcheung
    Oct 27, 2022 at 2:35
  • Slow down your Youtube video to playback rate of 0.25, you will see why it is not display the char smoothly...
    – hcheung
    Oct 27, 2022 at 2:54

1 Answer 1

2

Here are a few issues that I noticed in this code. I think that, if you manage to address them, you should get a smooth display:

  1. In the expression (temp_2>>(8-shift_step)-scroll), the amount of shift will be negative when scroll gets larger than 7. A righ shift by a negative amount is not a left shift: it is undefined behavior. Judging by the video, it seems the compiler does no shit at all in this case.

  2. If you want a one pixel space between the characters, you should move to the next character in the string every six pixels, thus the scroll variable should count from 0 to 5.

  3. Be aware that there could be up to three characters simultaneously (partially) displayed on the screen: when one character is centered, you should be able to see the edges of both its neighbors.

  4. As noted by hcheung in a comment, when you get to the last character in the string, the expression message[c+1] is reading past the end of that string.

9
  • You are right about the scrolling, I reduced the range of the scroll for to scroll<7 and it doesn't get stuck but the character fades earlier. I can't figure out the correct formula for when the scroll is greater than 6. Video: drive.google.com/file/d/1bkDzEiGrz1c6avpHSnl6ox7D34MD-mp9/… Oct 28, 2022 at 21:31
  • I tried to do this: if (scroll < 7) send_data((temp<<scroll) + (temp_2 >> 6-scroll)); else send_data((temp<<scroll) + (temp_2 << (scroll-6))); But it behaves strangely, the first character goes through, then it blinks, goes back and goes on again. Oct 28, 2022 at 21:33
  • @LucioMazzini: Hard to help debugging without seeing the whole code. That being said, I think the right formula should be send_data(temp<<scroll+6|temp_2<<scroll|temp_3>>6-scroll);. Oct 29, 2022 at 9:52
  • Where temp would be the current character, temp_2 the next character and temp_3 the character that comes after temp_2 right? Oct 29, 2022 at 11:57
  • 1
    Forget it, I already solved it. I started the mask at 0b10000 and scroll the mask to the right and the binary offset is 4-column. It works fine now, thanks. Oct 31, 2022 at 22:29

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