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Learn how to use RFID readers with your Arduino. In this instalment we use an RDM630 or RDM6300 RFID reader. If you have an Innovations ID-12 or ID-20 RFID reader, we have a different tutorial for you. This is chapter fifteen of our huge Arduino tutorial series. Updated 19/11/2013

Introduction
RFID – radio frequency identification. Some of us have already used these things, and they have become part of everyday life. For example, with electronic vehicle tolling, door access control, public transport fare systems and so on. It sounds complex – but isn’t.

To explain RFID for the layperson, we can use a key and lock analogy. Instead of the key having a unique pattern, RFID keys hold a series of unique numbers which are read by the lock. It is up to our Arduino sketch to determine what happens when the number is read by the lock. The key is the tag, card or other small device we carry around or have in our vehicles. We will be using a passive key, which is an integrated circuit and a small aerial. This uses power from a magnetic field associated with the lock. Some key or tag examples are shown in the image above.

Step 1: Getting Started

In this tutorial we’ll be using 125 kHz tags – for example. To continue with the analogy our lock is a small circuit board and a loop aerial. This has the capability to read the data on the IC of our key, and some locks can even write data to keys. Our reader (lock) example is show in the image above.
These readers are quite small and inexpensive – however the catch is that the loop aerial is somewhat fragile. If you need something much sturdier, consider the ID20 tags used in the other RFID tutorial.

Step 2: Setup Your RFID Reader

Setting up the RFID reader
This is a short exercise to check the reader works and communicates with the Arduino. You will need:

  1. Arduino Uno or compatible board and matching USB cable
  1. solderless breadboard
  1. three jumper wires
  1. the RFID reader package
  1. some RFID tags or cards
Simply insert the RFID reader main board into a solderless breadboard as shown below. Then use jumper wires to connect the second and third pins at the top-left of the RFID board to Arduino 5V and GND respectively. The RFID coil connects to the two pins on the top-right (they can go either way). Finally, connect a jumper wire from the bottom-left pin of the RFID board to Arduino digital pin 2 as shown above.

Step 3: Your First Arduino Sketch

Next, upload the following sketch to your Arduino and open the serial monitor window in the IDE:
// --------------------------------------------------------
#include <SoftwareSerial.h>
SoftwareSerial RFID(2, 3); // RX and TX
int i;
void setup()
{
RFID.begin(9600); // start serial to RFID reader
Serial.begin(9600); // start serial to PC
}
void loop()
{
if (RFID.available() > 0)
{
i = RFID.read();
Serial.print(i, DEC);
Serial.print(" ");
}
}
// --------------------------------------------------------

If you’re wondering why we used SoftwareSerial – if you connect the data line from the RFID board to the Arduino’s RX pin – you need to remove it when updating sketches, so this is more convenient.

Now start waving RFID cards or tags over the coil. You will find that they need to be parallel over the coil, and not too far away. You can experiment with covering the coil to simulate it being installed behind protective surfaces and so on. Watch this short video which shows the resulting RFID card or tag data being displayed in the Arduino IDE serial monitor.

As you can see from the example video, the reader returns the card’s unique ID number which starts with a 2 and ends with a 3. While you have the sketch operating, read the numbers from your RFID tags and note them down, you will need them for future sketches.

Step 4: Reading and Recognising RFID Cards

To do anything with the card data, we need to create some functions to retrieve the card number when it is read and place in an array for comparison against existing card data (e.g. a list of accepted cards) so your systems will know who to accept and who to deny. Using those functions, you can then make your own access system, time-logging device and so on.

Let’s demonstrate an example of this. It will check if a card presented to the reader is on an “accepted” list, and if so light a green LED, otherwise light a red LED. Use the hardware from the previous sketche, but add a typical green and red LED with 560 ohm resistor to digital pins 13 and 12 respectively. Then upload the following sketch:

//-------------------------------------------------------------------------------------------------------------
#include <SoftwareSerial.h>
SoftwareSerial RFID(2, 3); // RX and TX
int data1 = 0;
int ok = -1;
int yes = 13;
int no = 12;
// use first sketch in http://wp.me/p3LK05-3Gk to get your tag numbers
int tag1[14] = {2,52,48,48,48,56,54,66,49,52,70,51,56,3};
int tag2[14] = {2,52,48,48,48,56,54,67,54,54,66,54,66,3};
int newtag[14] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0}; // used for read comparisons
void setup()
{
RFID.begin(9600); // start serial to RFID reader
Serial.begin(9600); // start serial to PC
pinMode(yes, OUTPUT); // for status LEDs
pinMode(no, OUTPUT);
}
boolean comparetag(int aa[14], int bb[14])
{
boolean ff = false;
int fg = 0;
for (int cc = 0 ; cc < 14 ; cc++)
{
if (aa[cc] == bb[cc])
{
fg++;
}
}
if (fg == 14)
{
ff = true;
}
return ff;
}
void checkmytags() // compares each tag against the tag just read
{
ok = 0; // this variable helps decision-making,
// if it is 1 we have a match, zero is a read but no match,
// -1 is no read attempt made
if (comparetag(newtag, tag1) == true)
{
ok++;
}
if (comparetag(newtag, tag2) == true)
{
ok++;
}
}
void readTags()
{
ok = -1;
if (RFID.available() > 0)
{
// read tag numbers
delay(100); // needed to allow time for the data to come in from the serial buffer.
for (int z = 0 ; z < 14 ; z++) // read the rest of the tag
{
data1 = RFID.read();
newtag[z] = data1;
}
RFID.flush(); // stops multiple reads
// do the tags match up?
checkmytags();
}
// now do something based on tag type
if (ok > 0) // if we had a match
{
Serial.println("Accepted");
digitalWrite(yes, HIGH);
delay(1000);
digitalWrite(yes, LOW);
ok = -1;
}
else if (ok == 0) // if we didn't have a match
{
Serial.println("Rejected");
digitalWrite(no, HIGH);
delay(1000);
digitalWrite(no, LOW);
ok = -1;
}
}
void loop()
{
readTags();
}
// ------------------------------------------------------------------------------------

In the sketch we have a few functions that take care of reading and comparing RFID tags. Notice that the allowed tag numbers are listed at the top of the sketch, you can always add your own and more – as long as you add them to the list in the function checkmytags() which determines if the card being read is allowed or to be denied.

The function readTags() takes care of the actual reading of the tags/cards, by placing the currently-read tag number into an array which is them used in the comparison function checkmytags(). Then the LEDs are illuminated depending on the status of the tag at the reader. You can watch a quick demonstration of this example in this short video.

Conclusion

After working through this chapter you should now have a good foundation of knowledge on using the inexpensive RFID readers and how to call functions when a card is successfully read. For example, use some extra hardware (such as an N-MOSFET) to control a door strike, buzzer, etc. Now it’s up to you to use them as a form of input with various access systems, tracking the movement of people or things and much more.

And if you enjoyed the tutorial, or want to introduce someone else to the interesting world of Arduino – check out my book (now in a third printing!) “Arduino Workshop” from No Starch Press.

<p>Thanks for the tutorial, it was really helpful. However, I have a problem. After reading the tag for six times and accepting it, then it starts rejecting it. I noticed that from the seventh time and one, it does not read the elements of </p><p>int tag2[14] = {2, 53, 48, 48, 48, 49, 67, 56, 67, 70, 67, 51, 67, 3};</p><p>in the right order. Check the photo to understand what I mean</p>
<p>RFID.flush() doesn't appear to be working right?</p><p>I swipe the card and it shows Accepted and blinks 5-6 times...</p><p>Otherwise it seems to be working very nice.</p>
<p>can you tell how to add a tag and how in detail</p>
<p>You need to add a new variable tag3 for instance, then put the tag id in the same way the other two are inserted! </p><p>Now you need to change the check_cards function to also check if the card could be card number three!<br></p><p>Do you need more detail?</p>
<p>hello, how can i add more tags?</p><p>what i need to change? thanks</p>
<p>You need to add a new variable tag3 for instance, then put the tag id in the same way the other two are inserted! <br>Now you need to change the check_cards function to also check if the card could be card number three!<br><br></p>
<p>I NEED A RFID TO UNLOCK MY HEXPAD WHEN THE USER WIPES ONCE HOW AM I SUPPOSE TO DO</p>
<p>First disable your Capslock as it&acute;s a form of shouting online!<br>There are a few ways to your problem.</p><p>1. Have a boolean that is true only when you have swiped a &quot;good&quot; rfid card.</p><p>2. Wire the vcc pin of your keypad to a gpio pin of the arduino and hold that up for a given time frame.</p><p>3. Use your code structure in your loop(){} you just check for RFID Cards if there is one and the ID is correct then you proceed and read the keypad values (it&acute;s similar to version 1) if the card is not correct you just proceed to read for rfid cards... Make sure you deactivate the read of the keypad after the right code was entered(or after a given period of time) </p>
<p>Is this correct? why i got all 255?</p>
<p>My classmates and I were assigned a project using RFID to create an attendance system for our school. We are using Arduino UNO and the RDM6300. We need to first be able to read 6 tags. We are confused as to how we do this seeing that your code uses boolean and we need more than just a true of false. If anyone could please assist us it would be much appreciated.</p>
<p>Awesome :) I've just ordered the RDM6300 and some tags from Hobby Components. Is there a way to get the reader to adjust for 128 and 134.2 kHz chips as well? I want to be able to read all 3 frequencies of pet RFID chips.</p>
<p>How far the RFID reader can measure RFID tag ?</p>
Thanks for putting this out there. I'm hoping to use RFID tags in a project of mine using Bluetooth. I am already using software serial ports for my Bluetooth modules and am wondering if I can use the RFID tags on the hardware serial ports at the same time as the Bluetooth. Any help you can give me would be appreciated! Thanks in advance.
Great Instructable! Excuse my ignorance, but can you also program a reader to recognize or accept other items you may already have with an RFID chip? I'm not sure what other components might be in place to prevent that from functioning. For example, Disney has RFID chip embedded bracelets which are used for a variety of things around the park. Does it seem likely or unlikely that one could use other RFID embedded items to function with an Arduino RFID setup? I've not been able to discern whether or not this is generally possible.

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Bio: Technical person. Visit http://tronixstuff.com for Arduino and other tutorials, projects, kits, reviews and more. VK3FJBX http://arduinoworkshop.com
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