Is CharAt() the best method for me

Projects Programming
1

I am wondering if using a "CharAt()" method is a good idea for the following scenario:

I would define a string that has 26 values: "00110111000100010001110001" as an example.

I would step though the string reading each position using CharAt(x) one at a time.
I would then run subroutine "0" or subroutine "1" depending on the current CharAt(x) value.
Repeat 26 times by incrementing x.

Does this seem like a reasonable (and efficient) way to look at this desired behavior?? I have been staring at the Arduino reference site for quite a while.

(In case anyone is curious, I am trying to simulate an access control prox reader.)

Thanks for any advice.

2

Maybe? Are you using String class or c-string?

This?

If you have a String constant, yes, just juse CharAt(). If you are receiving the string of0's 1's from serial port, you should use c-string instead or at least reserve space ahead of time:

Most people don't use Strings on Arduino systems with only 2KB of ram.

3

Does this seem like a reasonable (and efficient) way to look at this desired behavior?? I have been staring at the Arduino reference site for quite a while.

Only if the data really is a string or String; A more efficient and compact method would be to use the bits of an integer like this.

long testData = 0b10100011100011100011100011100011;

void setup() 
{
  Serial.begin(115200);

  for (int bitCount = 31; bitCount >= 0; bitCount--)
  {
    byte thisBit = bitRead(testData, bitCount); 
    if (thisBit == 0)
    {
      zero();
    }
    else
    {
      one(); 
    }
  }
  Serial.println();
}

void zero()
{
  Serial.print(0);
}

void one()
{
  Serial.print(1);
}

void loop() 
{
}

Obviously the program is very artificial as it stands but it demonstrates the principles involved and the operation of bitRead() is very obvious.

4

Thank you both for your comments. This is why I like forums and support them whenever I can.

UKHeliBob's comment is spot-on with what I kinda knew must be out there, but didn't know how to ask. Thanks.

I hate being this green, but I shouldn't be for much longer.

James

5

Had to tell someone... AND THANK YOU for the help. I am on Cloud9 after taking this:

/*

 This code is a proof of concept for having an Arduino device mimic a 26bit wiegand card.

 Data is wiggled at 5mS interbit time.
 Pulse width is .3mS

  Pin14 is dZero
  Pin17 is dOne

 26bit wiegand
 bit1 = even parity, but is fixed at zero in this example
      parity is set to be ignored in Quintron sw
 bit2-9 = facility code, set to 774 decimal, 0000 0110 binary MSB
 bit10-25 = 16 bit value for UserID, set to 1 decimal, 0000 0001 binary MSB
 bit26 = odd parity, always zero
      parity is set to be ignored in Quintron sw

 Sequence is to send the "card read", wait 10 seconds, send the card read again.  
       

*/


// the setup routine runs once when you press reset;
// Give the pins each a name.
 int dZero = 4;
 int dOne = 7;
 // pulse is 100 microS;
 int pulse=100;
 // interBitDelay is 5mS;
 int interbitDelay=1;
 long randNumber;

void setup() {                

// initialize the serial communication:
  Serial.begin(9600);
  
// initialize the digital pin as an output.;
 pinMode(dZero, OUTPUT);     
 pinMode(dOne, OUTPUT);     
 digitalWrite(dZero, HIGH);   // Set voltage level high to start)
 digitalWrite(dOne, HIGH);    // Set voltage level high to start)
 

}


/*
  Basic loop, send card read, wait 7-10 seconds, repeat.

  Creating a "bit" is accomplished by driving the 
  appropriate data pin LOW for 100microS, returning to HIGH, 
  then DELAY 1mS to complete the bit transmission.
  
  
*/


void loop() {
//text send just before card read;
 Serial.println("Card read.");
 Serial.println("     ");
  
//  Bit 1: Parity bit, transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 2: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 3: transmit a one;
  digitalWrite(dOne, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dOne, HIGH);  
  delay(interbitDelay);  

//  Bit 4: transmit a one;
  digitalWrite(dOne, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dOne, HIGH);  
  delay(interbitDelay);  

//  Bit 5: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 6: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 7: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 8: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 9: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  


// NOW THE CARD NUMBER;

//  Bit 10: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 11: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 12: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 13: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 14: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 15: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 16: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 17: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 18: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 19: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 20: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 21: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 22: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 23: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 24: transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Bit 25: transmit a one;
  digitalWrite(dOne, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dOne, HIGH);  
  delay(interbitDelay);  

//  Bit 26: ending parity, transmit a zero;
  digitalWrite(dZero, LOW);
  delayMicroseconds(pulse);             
  digitalWrite(dZero, HIGH);  
  delay(interbitDelay);  

//  Pause for between 7 and 10 seconds;
  randNumber = random(5000, 8000);
 //Send data to the serial port each time a read occurs";
 Serial.println("Card data transmitted.");
 Serial.print("Random delay of ");
 Serial.print(randNumber);
 Serial.println("mS.");
 Serial.println("     ");
 delay(randNumber);
 
}

And just a few minutes later creating this using your help:

/*

Version 2,  this code is a proof of concept for having an Arduino 
device mimic a 37bit default card format wiegand card.

 Data is wiggled at 1mS interbit time.
 Pulse width is 100uS

  Pin14 is dZero
  Pin17 is dOne

 37bit wiegand
 bit1 = even parity, but is fixed at zero in this example
      parity is set to be ignored in Quintron sw
 bit2-17 = facility code, set to 774 decimal, 0110 0000 binary MSB
 bit18-36 = 19 bit value for UserID, set to 1 decimal, 0000 0001 binary MSB
 bit37 = odd parity, always zero
      parity is set to be ignored in Quintron sw

 Sequence is to send the "card read", wait 5-8 seconds, send the card read again.  
*/


// the setup routine runs once when you press reset;
// Give the pins each a name.
 int dZero = 4;
 int dOne = 7;
 int led = 13;
 // pulse is 100 microS;
 int pulse=100;
 // interBitDelay is 5mS;
 int interbitDelay=1;
 long randNumber;
// Card data is 37 bits;
// Card f/c code is 0000 0000 0100 0000;
// long cardData = 0b0000 0000 0110 0000 0000000000000000001;
 long cardData = 0b0000000000110000000000000000000000010;


void setup() {                

// initialize the serial communication:
  Serial.begin(9600);
  
// initialize the digital pin as an output.;
 pinMode(dZero, OUTPUT);     
 pinMode(dOne, OUTPUT);     
 digitalWrite(dZero, HIGH);   // Set voltage level high to start);
 digitalWrite(dOne, HIGH);    // Set voltage level high to start);
 digitalWrite(led, LOW);   // Set LED off to start);
}


/*
  Basic loop, send card read, wait 7-10 seconds, repeat.

  Creating a "bit" is accomplished by driving the 
  appropriate data pin LOW for 100microS, returning to HIGH, 
  then DELAY 1mS to complete the bit transmission.  
*/


void loop() {
//text send just before card read;
// Serial.println("Card read.");
// Serial.println("     ");

// Blink LED 13 to show card data sent;
 digitalWrite(led, HIGH);

  for (int bitCount = 36; bitCount >= 0; bitCount--)
  {
    byte currentBit = bitRead(cardData, bitCount); 
    if (currentBit == 0)
    {
      pulseD0();
    }
    else
    {
      pulseD1(); 
    }
  }
  Serial.println();

//  Pause for between 7 and 10 seconds;
  randNumber = random(5000, 8000);
 //Send data to the serial port each time a read occurs";
 Serial.println("Card data transmitted.");
 Serial.print("Random delay of ");
 Serial.print(randNumber);
 Serial.println("mS.");
 Serial.println("     ");
 delay(randNumber);
 

}
  
  void pulseD0() {
  
  //  Transmit a zero bit;
    digitalWrite(dZero, LOW);
    delayMicroseconds(pulse);             
    digitalWrite(dZero, HIGH);  
    delay(interbitDelay);  
    Serial.print("0");
  }

void pulseD1()
  {
  //  Transmit a one bit;
    digitalWrite(dOne, LOW);
    delayMicroseconds(pulse);             
    digitalWrite(dOne, HIGH);  
    delay(interbitDelay);
    Serial.print("1");  
  }

Freakin' amazing.