Hi arloG
Many thanks for replying. Yes, the inputs to the interrupts are negative-going pulses which come for the output of the card reader. There are usually 26 bits for a card read; each bit leaves the reader one at a time and from the appropriate output pin i.e. "1" bits are output from the "1" output pin and "0" bits are output from the "0" pin. This signal protocol is pretty slow with approximately 2ms between each pulse. The end of the card-read is usually determined by a timeout where no more pulses have been received after a period of time has elapsed.
Sorry about the code; I used the "copy for forum" option in the Arduino software but I must have done something wrong. Here is the code again - hopefully looking a bit clearer!
Best regards
Derek.
/*
* HID RFID Reader Wiegand Interface for Arduino Uno
* Written by Daniel Smith, 2012.01.30
* www.pagemac.com
*
* This program will decode the wiegand data from a HID RFID Reader (or, theoretically,
* any other device that outputs weigand data).
* The Wiegand interface has two data lines, DATA0 and DATA1. These lines are normall held
* high at 5V. When a 0 is sent, DATA0 drops to 0V for a few us. When a 1 is sent, DATA1 drops
* to 0V for a few us. There is usually a few ms between the pulses.
*
* Your reader should have at least 4 connections (some readers have more). Connect the Red wire
* to 5V. Connect the black to ground. Connect the green wire (DATA0) to Digital Pin 2 (INT0).
* Connect the white wire (DATA1) to Digital Pin 3 (INT1). That's it!
*
* Operation is simple - each of the data lines are connected to hardware interrupt lines. When
* one drops low, an interrupt routine is called and some bits are flipped. After some time of
* of not receiving any bits, the Arduino will decode the data. I've only added the 26 bit and
* 35 bit formats, but you can easily add more.
*/
#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 long 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
// interrupt that happens when INTO goes low (0 bit)
void ISR_INT0()
{
//Serial.print("0");
bitCount++;
flagDone = 0;
weigand_counter = WEIGAND_WAIT_TIME;
}
// interrupt that happens when INT1 goes low (1 bit)
void ISR_INT1()
{
//Serial.print("1");
databits[bitCount] = 1;
bitCount++;
flagDone = 0;
weigand_counter = WEIGAND_WAIT_TIME;
}
void setup()
{
pinMode(13, OUTPUT); // LED
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. ");
// we will decode the bits differently depending on how many bits we have
// see www.pagemac.com/azure/data_formats.php for mor info
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()
{
// I really hope you can figure out what this function does
Serial.print("FC = ");
Serial.print(facilityCode);
Serial.print(", CC = ");
Serial.println(cardCode);
}
Moderator edit:
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tags added.