Random

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

Hi,

Sorry I am very new at this. I was playing around with making a 7 segment led number light up. Then i thought it would be neat to make it display a random number. I am using random() but every time i use it i end up with 4. How do i get a real random number?

here is the code if anyone wish to see it:

//
int topBar = 12;
int middleBar = 11;
int bottomBar = 10;
//
int rightTBar = 9;
int rightBBar = 8;
//
int leftTBar = 7;
int leftBBar = 6;
//
int randNumber = 0;
//
int doOnce = 0;


void setup()                   
{
  pinMode(topBar, OUTPUT); 
  pinMode(middleBar, OUTPUT); 
  pinMode(bottomBar, OUTPUT);    
  pinMode(rightTBar, OUTPUT);   
  pinMode(rightBBar, OUTPUT);    
  pinMode(leftTBar, OUTPUT);     
  pinMode(leftBBar, OUTPUT);    
}

void setCharacter(int whichNum)
{
  if (whichNum == 0){
    // 0
    digitalWrite(topBar, LOW); 
    digitalWrite(middleBar, HIGH); 
    digitalWrite(bottomBar, LOW); 
    digitalWrite(rightTBar, LOW); 
    digitalWrite(rightBBar, LOW);  
    digitalWrite(leftTBar, LOW);
    digitalWrite(leftBBar, LOW);
  } 
  else if (whichNum == 1){
    // 1
    digitalWrite(topBar, HIGH); 
    digitalWrite(middleBar, HIGH); 
    digitalWrite(bottomBar, HIGH); 
    digitalWrite(rightTBar, LOW); 
    digitalWrite(rightBBar, LOW);  
    digitalWrite(leftTBar, HIGH);
    digitalWrite(leftBBar, HIGH);
  } 
  else if (whichNum == 2){
    // 2
    digitalWrite(topBar, LOW); 
    digitalWrite(middleBar, LOW); 
    digitalWrite(bottomBar, LOW); 
    digitalWrite(rightTBar, LOW); 
    digitalWrite(rightBBar, HIGH);  
    digitalWrite(leftTBar, HIGH);
    digitalWrite(leftBBar, LOW);
  } 
  else if (whichNum == 3){
    // 3
    digitalWrite(topBar, LOW); 
    digitalWrite(middleBar, LOW); 
    digitalWrite(bottomBar, LOW); 
    digitalWrite(rightTBar, LOW); 
    digitalWrite(rightBBar, LOW);  
    digitalWrite(leftTBar, HIGH);
    digitalWrite(leftBBar, HIGH);
  } 
  else if (whichNum == 4){
    // 4
    digitalWrite(topBar, HIGH); 
    digitalWrite(middleBar, LOW); 
    digitalWrite(bottomBar, HIGH); 
    digitalWrite(rightTBar, LOW); 
    digitalWrite(rightBBar, LOW);  
    digitalWrite(leftTBar, LOW);
    digitalWrite(leftBBar, HIGH);
  } 
  else if (whichNum == 5){
    // 5
    digitalWrite(topBar, LOW); 
    digitalWrite(middleBar, LOW); 
    digitalWrite(bottomBar, LOW); 
    digitalWrite(rightTBar, HIGH); 
    digitalWrite(rightBBar, LOW);  
    digitalWrite(leftTBar, LOW);
    digitalWrite(leftBBar, HIGH);
  } 
  else if (whichNum == 6){
    // 6
    digitalWrite(topBar, LOW); 
    digitalWrite(middleBar, LOW); 
    digitalWrite(bottomBar, LOW); 
    digitalWrite(rightTBar, HIGH); 
    digitalWrite(rightBBar, LOW);  
    digitalWrite(leftTBar, LOW);
    digitalWrite(leftBBar, LOW);
  } 
  else if (whichNum == 7){
    // 7
    digitalWrite(topBar, LOW); 
    digitalWrite(middleBar, HIGH); 
    digitalWrite(bottomBar, HIGH); 
    digitalWrite(rightTBar, LOW); 
    digitalWrite(rightBBar, LOW);  
    digitalWrite(leftTBar, HIGH);
    digitalWrite(leftBBar, HIGH);
  } 
  else if (whichNum == 8){
    // 8
    digitalWrite(topBar, LOW); 
    digitalWrite(middleBar, LOW); 
    digitalWrite(bottomBar, LOW); 
    digitalWrite(rightTBar, LOW); 
    digitalWrite(rightBBar, LOW);  
    digitalWrite(leftTBar, LOW);
    digitalWrite(leftBBar, LOW);
  } 
  else if (whichNum == 9){
    // 9
    digitalWrite(topBar, LOW); 
    digitalWrite(middleBar, LOW); 
    digitalWrite(bottomBar, LOW); 
    digitalWrite(rightTBar, LOW); 
    digitalWrite(rightBBar, LOW);  
    digitalWrite(leftTBar, LOW);
    digitalWrite(leftBBar, HIGH);
  }
  delay(50); 
}

void loop()
{
  if(doOnce == 0){
    for (int i=0; i <= 30; i++){
       randNumber = random(9);
      setCharacter(randNumber);
   }
  doOnce = 1;
  }
}
2

Here is a picture of it. The led is an old one i had picked up when i was a kid - it is a common anode one. I was hoping to get the number to stop on a random one every time i pressed the reset button, but it just likes 4 right now.

3

random() will return the same sequence of pseudo-random numbers unless you "seed" it with a truly
random number. See the reference page on random()

Getting truly random numbers is actually pretty tough. For dice-like applications, the usual solution is to use the extern human to help by using something like the number of milliseconds between the time the micro was reset and the time that the user hit a button, or the amount of time that the button is held down (in microseconds :-)) like:

void loop(void) {
  if (digitalRead(button) == 1) {
    myrandom = myrandom + 1;  /* count every loop while button is pressed */
  } else {
    if (myrandom > 0) {  /* Do we have a new random number */
      seg7display(myrandom % 9);
      myrandom = 0;   /* indicate number has been displayed
    }
  }
}
4

Another way to make a seed is to try and wire up a circuit which gives a random output.

Using a analog input and something like temperature comes to mind.
A clock would also work well.

5

Hi,

Thank you both for your replies. I went back and re-read the reference to random() and randomSeed() - made more sense this time.

I did as they suggest and did an analogRead on an empty port and the "noise" in that port was used as the seed. This is sort of like Cheaters solution - using a random output.

I also put my own switch in the circuit and tried it how westfw suggested - let it run while the button is down and then stop it on button release. That worked well too.

I guess i was just used to how flash works and i saw random() and ran with it.

Thanks again!