Arduino Duemilanove, 24 RFID Readers (wiegand26 type)

Projects General Guidance
1

Hi

I want to be able to connect up to 24 rfid readers to Arduino, I have been able to connect up to 8 but there are no more free pins. What chip/component should I use so I can connect the other rfid readers?

Cheers

2

Please share the code as this might trigger new ideas!

Can you tell more about the project, what you want to accomplish, are the readers far from each other

As I suppose it should be possible to handle them "simultaniously" you just don't have enough pins. did you test simultanious access for 8?

Option 1: take 3 Arduino's (and network them)
Option 2: take a MEGA
Option 3: hardware buffering per RFID, and do a round Robin

If you use NewSoftSerial you can declare the transmit pin to be -1 for the TX pin:
NSS RFID1(-1,3);
NSS RFID2(-1,4);
etc
This will make more RFID's per Arduino possible (so only 2 are needed) especially as you can use the analog pins as digital pins too.

3

Hi

Option 1 and 2 are out of consideration unfortunately. But option 3 seems interesting, although I have never heard of it, could you please elaborate on it? A little bit more on my project:

  • I have developed a board that uses Arduino Duemilanove schematics, but have also included 2 MCP23017 IO expanders, which I use to control the RFIDs and relays. In the following please find the code I'm trying to use for the MCP23017, there are some println just for debugging.
  • I'm getting some response from the reader, but I can not catch the tag ID correctly since I'm only getting at most 9 interrupts (but 26 are required, since we are using wiegand26 type reader).
#include <MCP23017.h>
#include <Wire.h>

#define INFTFA   0x0E
#define INFTFB   0x0F

int pressed = 0;
MCP23017 mcp(4);

void setup() {
  Wire.begin();
  Serial.begin(9600);
  Serial.println("Hello");
 
  // enable all interruptsc
  mcp.digitalRead(0);
  mcp.digitalRead(1);

  expanderWriteBoth(GPINTEN, 0x03);
  expanderWriteBoth(DEFVAL, 0x03);
  expanderWriteBoth(INTCON, 0x03);
  expanderWriteBoth(IODIR, 0xff);
//  mcp.writeRegister(IOCON, (byte)0x00);
  
  
//  mcp.writeRegister(GPINTEN, (byte)0x03);
//  mcp.writeRegister(DEFVAL, (byte)0x03);
//  mcp.writeRegister(INTCON, (byte)0x03);
 
  attachInterrupt(0, keypress, FALLING);
  //mcp.digitalWrite(0, HIGH);
}

// for example, IO direction
void expanderWriteBoth (const byte reg, const byte data ) 
{
  Wire.beginTransmission ((0x40 >>1) | (4 & 0x07));
  Wire.send (reg);
  Wire.send (data);  // port A
  Wire.send (data);  // port B
  Wire.endTransmission ();
} // end of expanderWrite

// read a byte from the expander
unsigned int expanderRead (const byte reg) 
{
  Wire.beginTransmission ((0x40 >>1) | (4 & 0x07));
  Wire.send (reg);
  Wire.endTransmission ();
  Wire.requestFrom ((0x40 >>1) | (4 & 0x07), 1);
  return Wire.receive();
} // end of expanderRead

int count = 0;

void loop() {
  if(pressed > 0) {
    Serial.println("Handling");
    handleKeypress();
    
    Serial.print("COUTN: ");
    Serial.println(count);
  }
}

volatile long reader = 0;

void keypress() {
  pressed++;
  reader = reader << 1;
  count++;
}

volatile long readerA = 0;
volatile long readerB = 0;

//for now, I am just defining 4 RFID readers, which corresponds to one port

volatile unsigned long reader1 = 0;
volatile unsigned long reader2 = 0;
volatile unsigned long reader3 = 0;
volatile unsigned long reader4 = 0;

volatile unsigned int reader1bits = 0;
volatile unsigned int reader2bits = 0;
volatile unsigned int reader3bits = 0;
volatile unsigned int reader4bits = 0;

void handleKeypress ()
{
  unsigned int interruptBit = 0;
  pressed = 0;
  count = 0;
  
  // Read port values, as required. Note that this re-arms the interrupts.
  if (mcp.readRegister (INFTFA))
    interruptBit |= mcp.readRegister (INTCAPA) << 8;    // read value at time of interrupt
  if (mcp.readRegister (INFTFB))
    interruptBit |= mcp.readRegister (INTCAPB);        // port B is in low-order byte
  
  for(int i = 0; i < 101; i++) {
    Serial.println(mcp.readRegister (INTCAPB));
    Serial.println(mcp.readRegister (GPIO));
  }
  
  //idea is to shift register to the right to find out which caused the interrupt, then shift either a 1 or a zero onto the reader value
  //reader 1
  if (interruptBit & 1)
    { //bit 0, indicating a 0 on reader 1, so shift a zero onto reader 1 value
    reader1 << 1;
    reader1bits++;
    }
  if (interruptBit & 2)
    { //bit 1, indicating a 1 on reader 1, so shift a one onto reader 1 value
    reader1 << 1;
    reader1++;
    reader1bits++;
    }
  //reader 2  
  if (interruptBit & 4)
    { //bit 2, indicating a 0 on reader 2, so shift a zero onto reader 2 value
    reader2 << 1;
    reader2bits++;
    }
  if (interruptBit & 8)
    { //bit 3, indicating a 1 on reader 2, so shift a one onto reader 2 value
    reader2 << 1;
    reader2++;
    reader2bits++;
    }
  //reader 3  
  if (interruptBit & 16)
    { //bit 4, indicating a 0 on reader 3, so shift a zero onto reader 3 value
    reader3 << 1;
    reader3bits++;
    }
  if (interruptBit & 32)
    { //bit 5, indicating a 1 on reader 3, so shift a one onto reader 3 value
    reader3 << 1;
    reader3++;
    reader3bits++;
    }
   //reader 4  
  if (interruptBit & 64)
    { //bit 6, indicating a 0 on reader 4, so shift a zero onto reader 4 value
    reader4 << 1;
    reader4bits++;
    }
  if (interruptBit & 128)
    { //bit 7, indicating a 1 on reader 4, so shift a one onto reader 4 value
    reader4 << 1;
    reader4++;
    reader4bits++;
    }
  
  
  
  mcp.digitalRead(0);
  mcp.digitalRead(1);
  
}  // end of handleKeypress

Thanks in advance