Monday, February 25, 2013

Arduino tutorial 15a – RFID with Innovations ID-20

Learn how to use RFID readers with your Arduino. In this instalment we use the Innovations ID-20 RFID reader. The ID-12 and ID-2 are also compatible. If you have the RDM630 RFID reader, we have a different tutorial.

This is part of a series originally titled “Getting Started with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.

Updated 26/02/2013

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. In this tutorial we’ll run through the basics of using the ID-20 module then demonstrate a project you can build and expand upon yourself.


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 software (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. Here are some key or tag examples:

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. And out reader is the Innovations ID-20 RFID reader:

Unlike the RDM630 reader in the other RFID tutorial – the ID-20 is a complete unit with an internal aerial and has much larger reader range of around 160 mm. It’s a 5V device and draws around 65 mA of current. If you have an ID-12 it’s the same except the reader range is around 120mm; and the ID-2 doesn’t have an internal aerial. Connecting your ID-20 reader to the Arduino board may present a small challenge and require a bit of forward planning. The pins on the back of the reader are spaced closer together than expected:

… so a breakout board makes life easier:

… and for demonstration and prototyping purposes, we’ve soldered on the breakout board with some header pins:

 The first thing we’ll do is connect the ID-20 and demonstrate reading RFID tags. First, wire up the hardware as shown below:

If you’re using the breakout board shown earlier, pin 7 matches “+/-” in the diagram above. Next, enter and upload the following sketch (download):

// Example 15a.1
#include <SoftwareSerial.h> SoftwareSerial id20(3,2); // virtual serial port char i; void setup()  { Serial.begin(9600); id20.begin(9600); }
void loop ()  { if(id20.available()) { i =; // receive character from ID20 Serial.print(i); // send character to serial monitor Serial.print(" "); } }

Note that we’re using a software serial port for our examples. In doing so it leaves the Arduino’s serial lines for uploading sketches and the serial monitor. Now open the serial monitor window, check the speed is set to 9600 bps and wave some tags over the reader – the output will be displayed as below (but with different tag numbers!):

Each tag’s number starts with a byte we don’t need, then twelve that we do, then three we don’t. The last three aren’t printable in the serial monitor. However you do want the twelve characters that appear in the serial monitor.  While running this sketch, experiment with the tags and the reader… get an idea for how far away you can read the tags. Did you notice the tag is only read once – even if you leave it near the reader? The ID-20 has more “intelligence” than the RDM630 we used previously. Furthermore when a tag is read, the ID-20 sends a short PWM signal from pin 10 which is  just under 5V and lasts for around 230 ms, for example (click image to enlarge):

 This signal can drive a piezo buzzer or an LED (with suitable resistor). Adding a buzzer or LED would give a good notification to the user that a card has been read. While you’re reading tags for fun, make a note of the tag numbers for your tags – you’ll need them for the next examples.

RFID Access System

Now that we can read the cards, let’s create a simple control system. It will read a tag, and if it’s in the list of allowed tags the system will do something (light a green LED for a moment). Plus we have another LED which stays on unless an allowed tag is read.  Wire up the hardware as shown below (LED1 is red, LED2 is green – click image to enlarge):

Now enter and upload the following sketch (download):

// Example 15a.2
#include  SoftwareSerial id20(3,2); // virtual serial port
// add your tags here. Don't forget to add to decision tree in readTag(); String Sinclair = "4F0023E2129C"; String Smythe = "4F0023CC9737"; String Stephen = "010044523C2B";
String testcard;  char testtag[12];  int indexnumber = 0;  char tagChar;
void setup()  { Serial.begin(9600); pinMode(7, OUTPUT); // this if for "rejected" red LED pinMode(9, OUTPUT); // this will be set high when correct tag is read. Use to switch something on, for now - a green LED.  id20.begin(9600);  digitalWrite(7, LOW); digitalWrite(9, LOW); }
void approved() // when an approved card is read { digitalWrite(9, HIGH); Serial.println("yes");  delay(1000); digitalWrite(9, LOW); }
void notApproved() // when an unlisted card is read { digitalWrite(7, HIGH); Serial.println("no"); delay(100); digitalWrite(7, LOW); }
void readTag() { tagChar =; if (indexnumber != 0) // never a zero in tag number { testtag[indexnumber - 1] = tagChar; } indexnumber++; if (indexnumber == 13 ) // end of tag number { indexnumber = 0; testcard = String(testtag); if (testcard.equals(Sinclair)) {  approved();  }  else if (testcard.equals(Smythe)) {  approved();  } else if (testcard.equals(Stephen)) {  approved();  } else {  notApproved();  } } }
void loop() { readTag(); }

In the function readCard() the sketch reads the tag data from the ID-20, and stores it in an array testtag[]. The index is -1 so the first unwanted tag number isn’t stored in the array. Once thirteen numbers have come through (the one we don’t want plus the twelve we do want) the numbers are smooshed together into a string variable testcard with the function String. Now the testcard string (the tag just read) can be compared against the three pre-stored tags (Sinclair, Smythe and Stephen).

Then it’s simple if… then… else to to see if we have a match, and if so – call the function approved() or disApproved as the case may be. In those two functions you store the actions you want to occur when the correct card is read (for example, control a door strike or let a cookie jar open) or when the system is waiting for another card/a match can’t be found. If you’re curious to see it work, check the following video where we take it for a test run and also show the distances that you have to work with:


Hopefully this short tutorial was of interest. We haven’t explored every minute detail of the reader – but you now have the framework to move forward with your own projects.

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