KickStart
b y M ik e T o o le y
Part 2: Getting started with RFID – working with cards and tags
Our occasional KickStart series aims to
show readers how to use readily available
low-cost components and devices to
solve a wide range of common problems
in the shortest possible time. Each of the
examples and projects can be completed
in no more than a couple of hours using
off-the-shelf parts. As well as briefly
explaining the underlying principles and
technology used, the series will provide
you with a variety of representative
solutions and examples, along with just
enough information to be able to adapt
and extend them for their own use.
Fig.2.1. Widely available RFID tags (left) and cards (right).
R
adio Frequency IDentification
(RFID) is a technology that
allows stored data to be
interrogated by radio without physical
contact. An RFID system comprises
two basic components: an RFID card
or tag, and an RFID reader. The latter
device is fitted with a small antenna
and the tags or cards can also contain
their own miniature antennas. The two
devices communicate wirelessly by
means of high-frequency radio signals.
The signal returned to the reader is
modulated with data stored in nonvolatile memory within the card or
tag. The received and demodulated
data stream is then passed from
the reader to a host computer or a
microcontroller system.
Low-cost plastic enclosures protect
cards and tags from their external
environment. Popular cards (such as
those manufactured by NXP) conform to
a standard credit-card size, while tags are
often designed to be used with key rings.
RFID systems can be either passive
or active. Passive RFID systems are
smaller and cheaper than active systems
40
This second instalment shows you
how to use low-cost RFID devices and,
in keeping with the KickStart philosophy,
we’ve provided sufficient information –
including some simple Arduino sketches
– for you to be able to incorporate RFID
into your own projects.
Fig.2.2. A popular MFRC522-based RFID module.
because there is no need for the card
or tag to incorporate its own power
source. Active systems can operate over
greater distances but are more complex
and expensive than their passive
counterparts. Note that passive cards
and tags must derive their power from
a reader (which must be present and
in close proximity) before data can be
returned to the reader.
The widely available NXP MIFARE
Classic RFID card is available at lowcost (around 25p when purchased in
quantity) and it measures 85.5 × 54mm
(ISO credit card size). The most widely
available cards incorporate 1KB of nonvolatile memory and the PVC laminated
surface can be printed on using a desktop
photo ID printer (note that they are
not compatible with standard inkjet
printers). Data storage time is quoted as,
‘a minimum of ten years’.
What can you do with RFID?
In recent years, low-cost modules have
become available to the enthusiast and
hobbyist making it possible to use them in
a wide range of applications. The reading
and writing is achieved using a compact
low-power wireless transceiver which,
Fig.2.3. Pin assignment for the MFRC522-based RFID module.
Practical Electronics | April | 2021
To ensure versatility, the MFRC522
provides support for three different host
interfaces:
n Serial Peripheral Interface (SPI) at up
to 10Mbit/s
n I2C-bus interface (at up to 400kBd
in fast mode and up to 3,400kBd in
high-speed mode)
n Serial UART (similar to RS232 but
with voltage levels dependant on the
supply voltage).
Fig.2.4. A simple RFID application based on an RC522 RFID module and an Arduino
Uno microcontroller.
together with a modest microcontroller
chip, allows you to read data from and
write data to cards and tags (see Fig.2.1).
Depending on the envisaged
application, an RFID reader can be
fixed or portable. In use, the reader is
placed close to the card or tag and held
briefly while the data is being read. Note
that only one card or tag can be read at
a time. Furthermore, care must be taken
to ensure that communication between
the reader and tag is not compromised
and the data being read is valid.
Commercial applications of RFID include
asset tracking, inventory management,
personnel tracking, access control,
maintenance, counterfeit prevention,
and supply chain management. When
compared with barcode scanning, a
significant advantage of RFID technology
is that there is no need for precise
alignment because the wireless data
stream can be read from a tag or card in
random orientation.
The MFRC522 chip’s internal clock
operates at 27.12MHz and the chip
requires a supply voltage of between
2.5V and 3.3V at typically up to 50mA. In
applications where power consumption
Fig.2.5. Wiring for the simple RFID application.
An RC-522 RFID module
A commonly available low-cost RC522 RFID module is shown in Fig.2.2.
This handy device will provide
you with a means of adding RFID
facilities to any SPI, I2C or UART-based
microcontroller. The RFID module is
based on an MFRC522 chip from NXP.
This device is a highly integrated reader/
writer designed to support contactless
communication conforming with
relevant ISO/IEC standards.
The chip’s internal transmitter
provides sufficient output to drive a
reader/writer antenna without the need
for any additional active circuitry. The
internal receiver incorporates circuitry
for demodulating and decoding 64-byte
signal blocks from compatible cards
and transponders, and its internal logic
manages framing and error detection
(parity and CRC) functionality. Speeds
of up to 848kBd (kilobaud) are supported
in both directions at an operating
frequency within the high-frequency
(HF) range at 13.56MHz.
Practical Electronics | April | 2021
Fig.2.6. Interstage piezo sounder driver circuit.
Table 2.1 Wiring an RC522 RFID module with the Uno’s SPI interface
RC522
module
Arduino
Uno
Wiring colour
(see Fig.2.5)
3.3V
3.3V
Red
3.3V power
RST
DIO9
Brown
Reset line
GND
GND
Black
Common ground / 0V
Notes
IRQ
N/C
MISO
DIO12
Orange
Not used
SPI data from the Uno to the RC522
MOSI
DIO11
Yellow
SPI data from the RC522 to the Uno
SCLK
DIO13
Green
Serial clock for SPI
SDA
DIO10
Blue
SPI SS chip enable
41
operation up to 240V AC at 2A. Both of these boards
require a 5V supply of around 150mA and both are
available at very modest cost from on-line suppliers
(see Going Further).
Coding the RFID module
Coding is straightforward using the Arduino IDE (see
Going Further) but will require the appropriate library
Fig.2.7. Semiconductor pin connections for Fig.2.6.
must be minimised, it is possible to use
the RC-522 in low-power standby mode to
reduce battery current. In this mode, the
module requires a mere 10µA of supply
current. A signal applied to the IRQ pin
can then be used to wake the module
ready for normal read/write operations.
A simple RFID application
To give you an idea of just how easy it is
to incorporate RFID in your own projects,
here’s a simple example in the form of
a basic RFID entry control application
based on an RFID-RC522 module and
an Arduino Uno, as shown in Fig.2.4.
The wiring from the RFID module to
the Arduino is shown in Fig.2.5. The
required connections based on the Uno’s
SPI interface are shown in Table 2.1.
An extra driver stage is needed
to supply adequate current to the
piezoelectric sounder (thus reducing the
load on the Arduino’s digital output port).
The circuit of the interstage driver is
shown in Fig.2.6, and the semiconductor
pin connections are shown in Fig.2.7.
Listing 2.1: This code (PE_KS_2-1.ino) reads the data stored on an RFID card or
tag when held close to the reader.
// MRFC522 Card Infodump V1.1
// Reads card or tag UID and dumps contents of memory
// Include the library routines
#include <SPI.h>
#include <MFRC522.h>
// Define the pins
#define RST_PIN 9
#define SS_PIN 10
// Create an instance of the MFRC522
MFRC522 mfrc522(SS_PIN, RST_PIN);
// Set-up code
void setup() {
Serial.begin(9600);
// Initialize serial port communication
SPI.begin();
// Initialise the SPI bus
mfrc522.PCD_Init();
// Initialise the MFRC522
Serial.println("Card Information Dump V1.1a");
Serial.println("Place the card or tag close to the reader and
wait until all data is read ...");
}
void loop() {
byte i;
Testing the RFID application
Since both audible and visual indications
are provided by the interstage relay
driver, our sample RFID system can be
tested without the external relay module
and door electronics. The external relay
module can be a low-cost module (see
Table 2.2, Going Further) and should be
suitably rated. Typical relay boards are
shown in Fig.2.8 and Fig.2.9. The relay
board in Fig.2.8 is rated for switching
AC of up to 250V at 10A and DC of up
to 30V at 10A. The solid-state relay
board shown in Fig.2.9 is suitable for AC
Fig.2.8. Off-the-shelf relay board.
42
// Is a card detected?
if (mfrc522.PICC_IsNewCardPresent())
{
// Can the serial number be read?
if (mfrc522.PICC_ReadCardSerial())
{
Serial.println();
Serial.print("Card detected : ");
mfrc522.PICC_DumpToSerial(&(mfrc522.uid));
}
}
}
Fig.2.9. Solid-state alternative relay board.
Practical Electronics | April | 2021
Fig.2.11. RFID tags labelled with unique
64-bit identifiers.
Fig.2.10. The data stored on a card or tag can be read using code like that in Listing 2.1.
which can be downloaded from the web.
Start the Arduino IDE and select Tools
and then Manage Libraries. From the
Library Manager enter ‘miguelbalboa’
(the library’s author) in the search box.
You should then see a library called:
MFRC522-spi-i2c-uart-async
Select the file and click on Install. The
new library file will then be downloaded
and installed, and the library list will be
updated accordingly. Click on Close and
return to the main IDE window. Enter the
sample code from Listing 2.1 (available
for download from the April 2021 page
of the PE website).
Make sure you save the file when you
have finished editing. Next, ensure that
you have the correct board type selected
(ie, Arduino Uno) and also that the
correct serial port has been selected (note
that both of these options are selected
from the IDE’s Tools menu). Finally,
select Sketch from the main menu and
Verify/Compile and Upload.
Table 2.2: Going Further with RFID cards and tags, and the Arduino Uno
Topic
Source
Notes
RFID
technology
Atlas RFID Store have a useful beginners’ guide to RFID:
http://bit.ly/pe-apr21-ks2-1
Another general introduction is at: http://bit.ly/pe-apr21-ks2-2
For innovative 13.6MHz RFID tags and applications:
http://bit.ly/pe-apr21-ks2-3
MFRC522
chip
The MFRC522 data sheets can be downloaded from NXP at:
http://bit.ly/pe-apr21-ks2-4
RC-522
RFID
module
RC-522 modules are available from several suppliers, including:
HobbyTronics at: http://bit.ly/pe-apr21-ks2-5
AZ-Delivery at: http://bit.ly/pe-apr21-ks2-6
Low-cost kits are available which include readers, tags and
cards. Cards and tags can be purchased very cheaply in
large quantities.
Arduino Uno
A detailed introduction to the hardware and software of the Arduino
Uno can be found in PE’s Electronics Teach-In 8.
http://bit.ly/pe-apr21-ks2-7
Arduino IDE
For a useful introduction and relevant theory see Part 1 of
Electronics Teach-In 8.
The latest version of the Arduino IDE can be downloaded from:
https://www.arduino.cc/en/software Versions are available for
Windows Linux and macOS. The current IDE version is 1.8.13.
http://bit.ly/pe-apr21-ks2-7
Interfacing
The author’s book, Electronic Circuits: Fundamentals and Applications
(5th Ed, 2020, Routledge) provides a general introduction to
microcontroller interfacing (Ch.15) and the Arduino Uno (Ch.19).
RFID library
The RC522 Arduino library can be downloaded from GitHub at:
https://github.com/miguelbalboa/rfid
The library can be downloaded using the IDE’s built-in library
manager (which is supported). Note that this library works
with Arduino IDE 1.6 (and later) but previous IDE versions are
not supported (causing potential compiler errors).
Relay
boards
Relay boards can be purchased at low cost from many suppliers,
including: AZ-Delivery, HobbyTronics, CPC/Farnell, Mouser, RS and
online suppliers.
Relay boards can be purchased with one, two, four or eight
relays, the latter is ideal for multi-channel operation.
Practical Electronics | April | 2021
43
Sample code listings
Our two sample listings show the simple
code necessary to test the application.
Listing 2.1 can be used to check a
card’s unique identifier (UID) and view
the stored data. Listing 2.2 provides
an example of how the reader can be
used in a simple access control system
(see Fig.2.4). Note that it is possible to
write data as well as read data and this
feature makes it possible to store and
subsequently update information on a
card or tag. Several useful and liberally
commented examples are provided in
Miguel Balboa’s library file.
The data returned from Listing 2.2
reveals the UID, which in this case is 79 2F
1D B5 (see Fig.2.10). Data is organised in
blocks and sectors. Each block comprises
64 bytes of data and there are 16 sectors on
the 1K MIFARE tag. The UID is contained
in the first four bytes in Sector 0, Block 0
(not shown in Fig.2.10, which only shows
the last three data blocks). Note that the UID
is written during manufacture and cannot
normally be changed (for test purposes I
found it useful to write a tag’s UID on the
tag, as shown in Fig.2.11). Finally, Fig.2.12
shows the frequency spectrum of the signal
produced by the RFID application. Note
that the signal is centred on approximately
13.56MHz and it occupies a bandwidth of
around 100kHz.
Going further
Table 2.2 lists sources to help you locate
components, information that will help
you with your own RFID applications
and links to useful background reading.
Fig.2.12. Spectral analysis of the 13.56MHz RFID signal.
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Practical Electronics | April | 2021
Listing 2.2: The code (PE_KS_2-2.ino) checks the unique data on a card or tag and will operate the relay and piezoelectric
sounder if (and only if) the correct card identifier (UID) is detected.
// MRFC522 Card Access Checker V2.1a
// Reads and checks card UID before activating relay and sounder
// Include the library routines
#include <SPI.h>
#include <MFRC522.h>
// Define the pins
#define RST_PIN 9
#define SS_PIN 10
#define sounder 7
#define relay 6
// Create an instance of the MFRC522
MFRC522 mfrc522(SS_PIN, RST_PIN);
// Set-up code
void setup() {
Serial.begin(9600);
// Initialize serial port communication
SPI.begin();
// Initialise the SPI bus
mfrc522.PCD_Init();
// Initialise the MFRC522
digitalWrite(relay, LOW); // Relay non-energized
digitalWrite(sounder, LOW); // No sound
Serial.println("Card Access Checker V1.1a");
Serial.println("Pleace your card or tag close to the reader ...");
}
void loop() {
byte i;
// Is a card detected?
if (mfrc522.PICC_IsNewCardPresent())
{
// Can the serial number be read?
if (mfrc522.PICC_ReadCardSerial())
{
// We have a card and its serial number so we can now format and verify the UID
String content = "";
for (byte i = 0; i < mfrc522.uid.size; i++)
{
content.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " "));
content.concat(String(mfrc522.uid.uidByte[i], HEX));
}
Serial.println();
Serial.print("Card detected : ");
content.toUpperCase();
if (content.substring(1) == "83 1D 3F 03") // Change this UID to suit the card
{
Serial.println("Access granted");
Serial.println();
// Beep door opening
digitalWrite(sounder, HIGH);
delay(500);
digitalWrite(sounder, LOW);
// Activate door relay
digitalWrite(relay, HIGH);
// Relay energized
delay(2500);
digitalWrite(relay, LOW);
// Relay non-energized
}
else
{
Serial.println("Access denied");
Serial.println();
delay(2500);
}
}
}
}
Practical Electronics | April | 2021
45
