Serial.print() kills my LEDs??

Forum 2005-2010 (read only) Software Syntax & Programs
1

i am playing around with a circular POV LED writer. i have defined my own pixel font and i got the LEDs writing the text OK :slight_smile: so far so good.

weird thing happens though.... if i comment out my own debugging Serial.print lines, my LEDs stop flashing!!! this is really puzzling me....
i have narrowed it down to the Serial.print line in LEDUpdate() routine....
can anyone help me?

i just updated to arduino0018 - this changed nothing

thanks!
/j

below is my code:

#include <avr/pgmspace.h>
#include <Flash.h>

int ledPin[8] = {
  2,3,4,5,6,7,8,9};

// this is the string to send to the sign - put it in program memory
FLASH_STRING (text,
    "     1. A ROBOT MAY NOT INJURE A HUMAN BEING OR, THROUGH INACTION, ALLOW A HUMAN BEING TO COME TO HARM.     "
    "     2. A ROBOT MUST OBEY ORDERS GIVEN TO IT BY HUMAN BEINGS EXCEPT WHERE SUCH ORDERS WOULD CONFLICT WITH THE FIRST LAW.     "
    "     3. A ROBOT MUST PROTECT ITS OWN EXISTENCE AS LONG AS SUCH PROTECTION DOES NOT CONFLICT WITH THE FIRST OR SECOND LAW.    " 
    ); 

FLASH_ARRAY (byte, characterData, 
  0,0,0,-6,-64,0,-64,40,-2,40,-2,40,100,-110,-1,-110,76,66,-92,72,16,36,74,
  -124,108,-110,-86,68,26,-64,124,-126,0,-126,124,80,32,-8,32,80,16,16,
  124,16,16,1,6,8,8,8,0,2,3,12,16,96,-128,124,-126,-126,-126,124,-128,-2,
  66,-122,-118,-110,98,68,-126,-110,-110,108,24,104,-120,-2,8,-12,-110,
  -110,-110,-116,124,-110,-110,-110,76,-128,-126,-116,-80,-64,108,-110,
  -110,-110,108,100,-110,-110,-110,124,0,34,1,38,16,40,68,40,40,40,68,40,
  16,64,-128,-118,-112,96,60,66,-71,-91,-87,-68,66,60,126,-112,-112,-112,
  126,-2,-110,-110,-110,108,124,-126,-126,-126,68,-2,-126,-126,-126,124,
  -2,-110,-110,-110,-126,-2,-112,-112,-112,-128,124,-126,-110,-108,94,-2,
  16,16,16,-2,-2,4,2,2,-4,-2,16,40,68,-126,-2,2,2,2,-2,64,32,16,32,64,-2,
  -2,64,56,4,-2,124,-126,-126,-126,124,-2,-112,-112,-112,96,124,-126,-126,
  -126,125,-2,-112,-104,-108,98,100,-110,-110,-110,76,-128,-128,-2,-128,
  -128,-4,2,2,2,-4,-64,56,6,56,-64,-4,2,2,-4,2,2,-4,-58,40,16,40,-58,-64,
  32,30,32,-64,-122,-118,-110,-94,-62,-1,-127,-127,-128,96,16,12,3,-127,
  -127,-1,64,-128,64,6,2,2,28,34,36,62,-2,18,34,28,28,34,34,20,28,34,36,
  -2,28,42,42,24,126,-96,-128,56,69,73,126,-2,16,32,30,-66,1,-66,-2,8,20,
  34,-2,62,16,32,30,16,32,30,62,16,32,30,28,34,34,28,127,36,68,56,56,68,
  72,127,62,16,32,18,42,36,32,-2,32,60,2,4,62,60,2,2,60,60,2,2,60,2,2,60,
  54,8,8,54,120,5,9,126,38,42,50,16,110,-127,-1,-127,110,16,64,-128,64,
  -128);
  
//index of each character
FLASH_ARRAY (int, characterIndex,
  0,2,4,7,12,17,24,29,30,32,35,40,45,47,50,52,57,62,64,69,74,79,84,89,94,
  99,104,106,108,111,114,117,122,130,135,140,145,150,155,160,165,170,
  171,175,180,184,191,196,201,206,211,216,221,226,231,236,243,248,253,
  258,261,266,269,272,275,275,279,283,287,291,295,298,302,306,307,309,
  313,314,321,325,329,333,337,340,343,346,350,354,361,365,369,372,375,
  376,379,383); //383 does not exist, is added to calculate width of char at 379
  
int maxStringSize;
int messageIndex;
char myChar;

void setup()   {                
  for (int i=0;i<8;i++) {
    pinMode(ledPin[i], OUTPUT); 
  }
  maxStringSize =  text.length();  // find message size
}
  
void loop()                     
{ 
  myChar =  text[messageIndex]-32; //we start ASCII table at SPACE
  
  LEDUpdate();

  messageIndex++;
  messageIndex = messageIndex % maxStringSize;

}

void LEDUpdate() {
  int dataIndex = characterIndex[myChar];
  
  Serial.print(dataIndex); // if i remove this one the LEDs don't update???
  
  int charWidth = characterIndex[myChar+1]-dataIndex;
  
  for (int i=0;i<charWidth;i++) {
    byte dataValue = characterData[dataIndex+i];
    for (int j=0;j<8;j++) {      
      int bitValue = bitRead(dataValue,j);
      if (bitValue == 0) { //LEDs are active low
        digitalWrite(ledPin[j], HIGH); 
      } else {
        digitalWrite(ledPin[j], LOW);
      }
    }
    delay(1); //pause for pixel width
  }
  
  //insert space between characters
  for (int i=0;i<8;i++) {
    digitalWrite(ledPin[i], HIGH); //all black
  }
  delay(2); //pause for space
}
2

No baud rate set - how does that work?

3

Hi, I suspect there is a "delay" caused by the Serial.print() allowing the LEDs to work.

The delays you are using are VERY short ( 1/1000 th of a second). Try a delay of a whole second -- delay(1000);

And Groove is right, you should also initialize the UART by setting the baud rate. You will thank us for this on your future projects...

4

sorry guys, when cleaning out my code before posting it, i deleted the Serial.begin(2400); line -- ofcourse i need this :slight_smile:

i also need the small delays, since my LEDs are rotating at quite high speed -- so leaving them on/off for about 1/1000 of a second is about right for the pixel width i am after. next step is tweaking the code for more precise LED calibration, but i need serial communication over wireless for this, hence this post. :wink:

thanks for the debug tips. the problem still persist -- even if i set the delay for a full second

but for kicks, i tried entering a small delay(1) in stead of the serial.print() command -- and this works! the LEDs are blinking happily when the delay is in there. hm.... i have no idea why the small delay is needed, but for now my problems are solved i guess....

working code:

#include <avr/pgmspace.h>
#include <Flash.h>

int ledPin[8] = {
  2,3,4,5,6,7,8,9};

// this is the string to send to the sign - put it in program memory
FLASH_STRING (text,
    "     1. A ROBOT MAY NOT INJURE A HUMAN BEING OR, THROUGH INACTION, ALLOW A HUMAN BEING TO COME TO HARM.     "
    "     2. A ROBOT MUST OBEY ORDERS GIVEN TO IT BY HUMAN BEINGS EXCEPT WHERE SUCH ORDERS WOULD CONFLICT WITH THE FIRST LAW.     "
    "     3. A ROBOT MUST PROTECT ITS OWN EXISTENCE AS LONG AS SUCH PROTECTION DOES NOT CONFLICT WITH THE FIRST OR SECOND LAW.    " 
    ); 

FLASH_ARRAY (byte, characterData, 
  0,0,0,-6,-64,0,-64,40,-2,40,-2,40,100,-110,-1,-110,76,66,-92,72,16,36,74,
  -124,108,-110,-86,68,26,-64,124,-126,0,-126,124,80,32,-8,32,80,16,16,
  124,16,16,1,6,8,8,8,0,2,3,12,16,96,-128,124,-126,-126,-126,124,-128,-2,
  66,-122,-118,-110,98,68,-126,-110,-110,108,24,104,-120,-2,8,-12,-110,
  -110,-110,-116,124,-110,-110,-110,76,-128,-126,-116,-80,-64,108,-110,
  -110,-110,108,100,-110,-110,-110,124,0,34,1,38,16,40,68,40,40,40,68,40,
  16,64,-128,-118,-112,96,60,66,-71,-91,-87,-68,66,60,126,-112,-112,-112,
  126,-2,-110,-110,-110,108,124,-126,-126,-126,68,-2,-126,-126,-126,124,
  -2,-110,-110,-110,-126,-2,-112,-112,-112,-128,124,-126,-110,-108,94,-2,
  16,16,16,-2,-2,4,2,2,-4,-2,16,40,68,-126,-2,2,2,2,-2,64,32,16,32,64,-2,
  -2,64,56,4,-2,124,-126,-126,-126,124,-2,-112,-112,-112,96,124,-126,-126,
  -126,125,-2,-112,-104,-108,98,100,-110,-110,-110,76,-128,-128,-2,-128,
  -128,-4,2,2,2,-4,-64,56,6,56,-64,-4,2,2,-4,2,2,-4,-58,40,16,40,-58,-64,
  32,30,32,-64,-122,-118,-110,-94,-62,-1,-127,-127,-128,96,16,12,3,-127,
  -127,-1,64,-128,64,6,2,2,28,34,36,62,-2,18,34,28,28,34,34,20,28,34,36,
  -2,28,42,42,24,126,-96,-128,56,69,73,126,-2,16,32,30,-66,1,-66,-2,8,20,
  34,-2,62,16,32,30,16,32,30,62,16,32,30,28,34,34,28,127,36,68,56,56,68,
  72,127,62,16,32,18,42,36,32,-2,32,60,2,4,62,60,2,2,60,60,2,2,60,2,2,60,
  54,8,8,54,120,5,9,126,38,42,50,16,110,-127,-1,-127,110,16,64,-128,64,
  -128);
  
//index of each character
FLASH_ARRAY (int, characterIndex,
  0,2,4,7,12,17,24,29,30,32,35,40,45,47,50,52,57,62,64,69,74,79,84,89,94,
  99,104,106,108,111,114,117,122,130,135,140,145,150,155,160,165,170,
  171,175,180,184,191,196,201,206,211,216,221,226,231,236,243,248,253,
  258,261,266,269,272,275,275,279,283,287,291,295,298,302,306,307,309,
  313,314,321,325,329,333,337,340,343,346,350,354,361,365,369,372,375,
  376,379,383); //383 does not exist, is added to calculate width of char at 379
  
int maxStringSize;
int messageIndex;
char myChar;

void setup()   {                
  for (int i=0;i<8;i++) {
    pinMode(ledPin[i], OUTPUT); 
  }
  maxStringSize =  text.length();  // find message size
  Serial.begin(2400);
}
  
void loop()                     
{ 
  myChar =  text[messageIndex]-32; //we start ASCII table at SPACE
  
  LEDUpdate();

  messageIndex++;
  messageIndex = messageIndex % maxStringSize;

}

void LEDUpdate() {
  int dataIndex = characterIndex[myChar];
  
  //Serial.print(dataIndex); // if i remove this one the LEDs don't update???
  
  delay(1); //but when this is entered it works again...
  
  int charWidth = characterIndex[myChar+1]-dataIndex;
  
  for (int i=0;i<charWidth;i++) {
    byte dataValue = characterData[dataIndex+i];
    for (int j=0;j<8;j++) {      
      int bitValue = bitRead(dataValue,j);
      if (bitValue == 0) { //LEDs are active low
        digitalWrite(ledPin[j], HIGH); 
      } else {
        digitalWrite(ledPin[j], LOW);
      }
    }
    delay(1); //pause for pixel width
  }
  
  //insert space between characters
  for (int i=0;i<8;i++) {
    digitalWrite(ledPin[i], HIGH); //all black
  }
  delay(2); //pause for space
}