Overview of RFID 

• Radio frequency Identification i.e. RFID is a wireless identification technology that uses radio waves to identify the presence of RFID tags.
• Just like Bar code reader, RFID technology is used for identification of people, object etc. presence.
• In barcode technology, we need to optically scan the barcode by keeping it in front of reader, whereas in RFID technology we just need to bring RFID tags in range of readers. Also, barcodes can get damaged or unreadable, which is not in the case for most of the RFID.
• RFID is used in many applications like attendance system in which every person will have their separate RFID tag which will help identify person and their attendance.
• RFID is used in many companies to provide access to their authorized employees.
• It is also helpful to keep track of goods and in automated toll collection system on highway by embedding Tag (having unique ID) on them.

RFID based system has two basic elements

1. RFID Tag:

RFID tag includes microchip with radio antenna mounted on substrate which carries 12 Byte unique Identification number.

2.  RFID Reader:

It is used to read unique ID from RFID tags. Whenever RFID tags comes in range, RFID reader reads its unique ID and transmits it serially to the microcontroller or PC. RFID reader has transceiver and an antenna mounted on it. It is mostly fixed in stationary position.

Basically, RFID systems categorized as active and passive based on how they are powered and their range.

1.      Active RFID system

Active RFID tags have their own transmitter and power source (Mostly battery operated). They operate at 455 MHz, 2.45 GHz, or 5.8 GHz, and they typically have a read range of 60 feet to 300 feet (20 meters to 100 meters).

2.      Passive RFID system

Passive RFID tags do not have a transmitter, they simply reflect energy (radio waves) back coming from the RFID reader antenna. They operate in Low frequency (~125 kHz) as well as High frequency (~13 MHz) band and have limited read range of up to ~1m.

There are two modes of coupling for communication used in RFID as,

Inductive coupling, in which RFID reader emits magnetic field and whenever RFID tags enters the magnetic field which creates energy response from RFID tags and is detected by RFID reader. As the magnetic field drops sharply with distance, it is used for short distance applications.

Capacitive coupling, where reader emits electromagnetic waves and whenever that waves encounters RFID tags, RFID tag reflects signal containing information of ID.

How RFID system works?

RFID Reader has transceiver which generates a radio signal and transmits it through antenna. This signal itself is in the form of energy which is used to activate and power the tag.

When RFID tag comes in range of signal transmitted by the reader, transponder in the tag is hit by this signal. A tag draws power from the electromagnetic field created by reader. Then, the transponder converts that radio signal into the usable power. After getting power, transponder sends all the information it has stored in it, such as unique ID to the RFID reader in the form of RF signal. Then, RFID reader puts this unique ID data in the form of byte on serial Tx (transmit) pin. This data can be used or accessed by PC or microcontroller serially using UART communication.

There are various RFID readers available according to their frequency are shown as follows,

EM18 RFID Reader

EM18 is a RFID reader which is used to read RFID tags of frequency 125 kHz.

After reading tags, it transmits unique ID serially to the PC or microcontroller using UART communication or Wiegand format on respective pins.

EM18 RFID reader reads the data from RFID tags which contains stored ID which is of 12 bytes. 

EM18 RFID reader doesn’t require line-of-sight. Also, it has identification range which is short i.e. in few centimeters.

RFID reader EM-18 features:

1.      Serial RS232/TTL output

2.      Operating Frequency is 125KHz.

3.      Range is 5-8 cm.

Specification of RFID EM18

• Operating frequency: 125kHz
• Operating voltage: DC 5V
• Supply current: <50mA
• Read distance: up to 100mm (depending on the tag used)
• Interface: UART (TTL level)
• Dimensions: 40mm x 40mm x 16mm
• Communication protocol: UART
• Baud rate: 9600, 8, N, 1

Alternate options for RFID EM18

• RFID RC522
• RFID RC531
• RFID RC632
• RFID RDM6300

RFID Reader to PC/Laptop communication

We can see RFID reader output on serial terminal of PC/Laptop.

When we bring RFID tag near to the reader, it reads the data from the tag and immediately transmits 12-byte unique ID on the serial port.

12 Byte Unique Identification Number

RFID Tags contain 12 Byte unique ID.

These checksum bytes will be the XOR result of 1st 10 bytes, i.e. Tag no.

Examples of RFID Reader interfacing

1. RFID Reader Interfacing with PIC18F4550
2. RFID Reader Interfacing with ATmega16
3. RFID Reader Interfacing with 8051