hid-prox-weigand.ino

/*
 * HID RFID Reader Wiegand Interface for Arduino Uno
 * Originally by  Daniel Smith, 2012.01.30 -- http://www.pagemac.com/projects/rfid/arduino_wiegand
 * 
 * Updated 2016-11-23 by Jon "ShakataGaNai" Davis.
 * See https://obviate.io/?p=7470 for more details & instructions
*/
 
 
#define MAX_BITS 100                 // max number of bits 
#define WEIGAND_WAIT_TIME  3000      // time to wait for another weigand pulse.  
 
unsigned char databits[MAX_BITS];    // stores all of the data bits
unsigned char bitCount;              // number of bits currently captured
unsigned char flagDone;              // goes low when data is currently being captured
unsigned int weigand_counter;        // countdown until we assume there are no more bits
 
unsigned long facilityCode=0;        // decoded facility code
unsigned long cardCode=0;            // decoded card code

int LED_GREEN = 11;
int LED_RED = 12;
int BEEP_BEEP = 10;

// interrupt that happens when INTO goes low (0 bit)
void ISR_INT0() {
  //Serial.print("0");   // uncomment this line to display raw binary
  bitCount++;
  flagDone = 0;
  weigand_counter = WEIGAND_WAIT_TIME;  
 
}
 
// interrupt that happens when INT1 goes low (1 bit)
void ISR_INT1() {
  //Serial.print("1");   // uncomment this line to display raw binary
  databits[bitCount] = 1;
  bitCount++;
  flagDone = 0;
  weigand_counter = WEIGAND_WAIT_TIME;  
}
 
void setup() {
  pinMode(LED_RED, OUTPUT);  
  pinMode(LED_GREEN, OUTPUT);  
  pinMode(BEEP_BEEP, OUTPUT);  
  digitalWrite(LED_RED, HIGH); // High = Off
  digitalWrite(BEEP_BEEP, HIGH); // High = off
  digitalWrite(LED_GREEN, LOW);  // Low = On
  pinMode(2, INPUT);     // DATA0 (INT0)
  pinMode(3, INPUT);     // DATA1 (INT1)
 
  Serial.begin(9600);
  Serial.println("RFID Readers");
 
  // binds the ISR functions to the falling edge of INTO and INT1
  attachInterrupt(0, ISR_INT0, FALLING);  
  attachInterrupt(1, ISR_INT1, FALLING);
 
 
  weigand_counter = WEIGAND_WAIT_TIME;
}
 
void loop()
{
  // This waits to make sure that there have been no more data pulses before processing data
  if (!flagDone) {
    if (--weigand_counter == 0)
      flagDone = 1;  
  }
 
  // if we have bits and we the weigand counter went out
  if (bitCount > 0 && flagDone) {
    unsigned char i;
 
    Serial.print("Read ");
    Serial.print(bitCount);
    Serial.print(" bits. ");
 
    if (bitCount == 35) {
      // 35 bit HID Corporate 1000 format
      // facility code = bits 2 to 14
      for (i=2; i<14; i++) {
         facilityCode <<=1;
         facilityCode |= databits[i];
      }
 
      // card code = bits 15 to 34
      for (i=14; i<34; i++) {
         cardCode <<=1;
         cardCode |= databits[i];
      }
 
      printBits();
    }
    else if (bitCount == 26) {
      // standard 26 bit format
      // facility code = bits 2 to 9
      for (i=1; i<9; i++) {
         facilityCode <<=1;
         facilityCode |= databits[i];
      }
 
      // card code = bits 10 to 23
      for (i=9; i<25; i++) {
         cardCode <<=1;
         cardCode |= databits[i];
      }
 
      printBits();  
    }
    else {
     // you can add other formats if you want!
     // Serial.println("Unable to decode."); 
    }
 
     // cleanup and get ready for the next card
     bitCount = 0;
     facilityCode = 0;
     cardCode = 0;
     for (i=0; i<MAX_BITS; i++) 
     {
       databits[i] = 0;
     }
  }
}
 
void printBits() {
      Serial.print("FC = ");
      Serial.print(facilityCode);
      Serial.print(", CC = ");
      Serial.println(cardCode);

      // Now lets play with some LED's for fun:
      digitalWrite(LED_RED, LOW); // Red
      if(cardCode == 12345){
        // If this one "bad" card, turn off green
        // so it's just red. Otherwise you get orange-ish
        digitalWrite(LED_GREEN, HIGH); 
      }
      delay(500);
      digitalWrite(LED_RED, HIGH);  // Red Off
      digitalWrite(LED_GREEN, LOW);  // Green back on
 
      // Lets be annoying and beep more
      digitalWrite(BEEP_BEEP, LOW);
      delay(500);
      digitalWrite(BEEP_BEEP, HIGH);
      delay(500);
      digitalWrite(BEEP_BEEP, LOW);
      delay(500);
      digitalWrite(BEEP_BEEP, HIGH);
}

@Bjeurn2:

Not the author, but I suspect I can answer your questions:

1. char just means a 1-byte value, and can be used numerically (think like the ordinal of a value, 'A' == 65, etc). If the author had declared it as an int, it would be 4 bytes long, which was not needed in this case.
2. the databits structure is initialized to all zeros on line 123, so there's no need to write a zero. Essentially what's going on is you have a buffer and a pointer into it (e.g. [0]00000). If you read a zero, just move the pointer ([0]00000 -> 0[0]0000), while if you read a one you need to overwrite the value and then move the pointer (0[0]0000 -> 0[1]0000 -> 01[0]000)
3. lines 84 and 90 shift the value one bit to the left, and then or in the new value pulled from databits. Those lines aren't resetting the values, they're completing them, after which printBits() is called on line 94, after which the values are reset on lines 119 and 120.

Hey, I love the code, it is the only one I could find that I could edit to decode my 36bit badge!

I'm not done troubleshooting yet, but can you think of any reason this code would crash an Arduino if left to run for over a few hours? I know I have the raw option enabled, but none of the data is stored to a cache or ram or anything like that, correct? (Sorry, I'm a noob).

Thanks!!

@SpeedGP

if left to run for over a few hours

I don't see a reason why it would be a problem. The code does very very little beyond exactly what is required to decode the bits. There is a small memory of stuff, but only used to keep track of the bits coming in. If it's been longer than 3 seconds since the bits came in, then that memory is reset.

In short, I can't see any reason why it would be a problem, but I never actually tested this in production.