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RFID Card Reader, Serial (#28140)
RFID Card Reader, USB (#28340)
Introduction
Designed in cooperation with Grand Idea Studio (www.grandideastudio.com), the Parallax Radio
Frequency Identification (RFID) Card Readers provide a low-cost solution to read passive RFID
transponder tags up to 4 inches away. The RFID Card Readers can be used in a wide variety of hobbyist
and commercial applications, including access control, user identification, robotics navigation, inventory
tracking, payment systems, car immobilization, and manufacturing automation. The RFID Card Reader is
available in two versions: A TTL-level serial interface for use with a microcontroller and a USB interface
for direct connection to a computer.
Features
Low-cost method for reading passive, 125 kHz RFID transponder tags
Two easy-to-use versions: Serial interface for microcontrollers and USB for direct connection to
PC, Macintosh, or Linux machines
Bi-color LED for visual indication of status
Copyright © Parallax Inc. RFID Card Reader Serial & USB (#28140 / 28340)
v2.2 3/22/2010 Page 1 of 11
RFID Compatibility
The Parallax RFID Card Reader works exclusively with the EM Microelectronics EM4100-family of passive
read-only transponder tags. Each transponder tag contains a unique, read-only identifier (one of 2
40
, or
1,099,511,627,776 possible combinations).
A variety of different tag types and styles exist with the most popular made available from Parallax.
Connections (Serial)
The Parallax RFID Card Reader Serial version easily interfaces to any host microcontroller using only four
connections (VCC, /ENABLE, SOUT, GND).
Pin
1
2
3
4
Pin Name
VCC
/ENABLE
SOUT
GND
Type
P
I
O
G
Function
System power. +5V DC input.
Module enable pin. Active LOW digital input. Bring this pin LOW to
enable the RFID reader and activate the antenna.
Serial output to host. TTL-level interface, 2400 bps, 8 data bits, no parity,
1 stop bit.
System ground. Connect to power supply’s ground (GND) terminal.
Note: Type: I = Input, O = Output, P = Power, G = Ground
Use the following example circuit for connecting the Parallax RFID Card Reader:
Copyright © Parallax Inc.
RFID Card Reader Serial & USB (#28140 / 28340)
v2.2 3/22/2010 Page 2 of 11
Connections (USB)
The Parallax RFID Card Reader USB version can be connected directly to any PC, Macintosh, or Linux
machine that has a USB port and the appropriate drivers installed. The module is powered from the host
computer’s USB port and uses an industry-standard FTDI FT232R device to provide the USB connectivity.
FTDI drivers are available from www.ftdichip.com/Drivers/VCP.htm.
Signal
RX
DTR
Port Name
Serial Receive
Data Terminal Ready
Function
Serial output to host. 2400 bps, 8 data bits, no parity, 1 stop bit.
Module enable. Bring the DTR line HIGH to enable the RFID
reader and activate the antenna. Bring the DTR line LOW to
disable the RFID reader.
When the Parallax RFID Card Reader is connected to the host computer, it will appear as a Virtual COM
port and will have a COM port number automatically assigned to it. This COM port can be accessed by
any software application, programming language, or interface that provides COM port connectivity and
will allow you to read the data stream transmitted by the module.
An example program, including Visual Basic/VB.net source code, for reading tags in Windows XP/Vista is
available on the Parallax website at http://forums.parallax.com/forums/default.aspx?f=21&m=269675.
The DEBUG window within the Parallax BASIC Stamp Editor (www.parallax.com/tabid/441/Default.aspx)
provides functionality to set the state of a COM port’s DTR line. Checking the DTR box in the toolbar will
activate the RFID Card Reader.
Copyright © Parallax Inc.
RFID Card Reader Serial & USB (#28140 / 28340)
v2.2 3/22/2010 Page 3 of 11
Usage
A visual indication of the state of the RFID Card Reader is given with the on-board LED. When the
module is successfully powered-up and is in an idle state, the LED will be GREEN. When the module is in
an active state searching for or communicating with a valid tag, the LED will be RED.
The RFID Card Reader Serial version is activated via the /ENABLE pin on the module’s 4-pin header.
When the RFID Card Reader is powered and /ENABLE is pulled LOW, the module will enter the active
state. When /ENABLE is pulled HIGH or left unconnected, the module will enter the idle state.
The RFID Card Reader USB version is activated via the DTR line of the USB Virtual COM port. When the
DTR line is set HIGH, the module will enter the active state. When the DTR line is set LOW, the module
will enter the idle state.
The face of the RFID tag should be held parallel to the front or back face of the antenna (where the
majority of RF energy is emitted). If the tag is held sideways (for example, perpendicular to the
antenna), you’ll either get no reading or a poor reading distance. Only one transponder tag should be
held up to the antenna at any time. The use of multiple tags at one time will cause tag collisions and the
reader may not detect any of them. The tags available in the Parallax store have a read distance of
approximately 4 inches. Actual distance may vary slightly depending on the size of the transponder tag
and environmental conditions of the application.
Communication Protocol
All communication is 8 data bits, no parity, 1 stop bit, and least significant bit first (8N1) at 2400 bps.
The RFID Card Reader Serial version transmits data as 5V TTL-level, non-inverted asynchronous serial.
The RFID Card Reader USB version transmits the data through the USB Virtual COM Port driver. This
allows easy access to the serial data stream from any software application, programming language, or
interface that can communicate with a COM port.
When the RFID Card Reader is active and a valid RFID transponder tag is placed within range of the
activated reader, the tag’s unique ID will be transmitted as a 12-byte printable ASCII string serially to the
host in the following format:
Start Byte
(0x0A)
Unique ID
Digit 1
Unique ID
Digit 2
Unique ID
Digit 3
Unique ID
Digit 4
Unique ID
Digit 5
Unique ID
Digit 6
Unique ID
Digit 7
Unique ID
Digit 8
Unique ID
Digit 9
Unique ID
Digit 10
Stop Byte
(0x0D)
The start byte and stop byte are used to easily identify that a correct string has been received from the
reader (they correspond to line feed and carriage return characters, respectively). The middle ten bytes
are the actual tag's unique ID. For example, for a tag with a valid ID of 0F0184F07A, the following bytes
would be sent: 0x0A, 0x30, 0x46, 0x30, 0x31, 0x38, 0x34, 0x46, 0x30, 0x37, 0x41, 0x0D.
Interference
The Parallax RFID Card Reader, like many RF devices, may experience RF noise in its frequency range.
This may cause the reader to transmit a spurious tag response when no tag is near the unit. This will not
affect most uses of the RFID Card Reader. To avoid treating spurious responses as legitimate tags, it is
recommended to read two responses in a row within a given amount of time (for example, one second)
to ensure that you are reading a valid tag and not a “tag” generated by noise.
Copyright © Parallax Inc.
RFID Card Reader Serial & USB (#28140 / 28340)
v2.2 3/22/2010 Page 4 of 11
DC Characteristics
At V
CC
= +5.0V and T
A
= 25ºC unless otherwise noted
Parameter
Supply Voltage
Supply Current, Idle
Supply Current, Active
Input LOW voltage
Input HIGH voltage
Output LOW voltage
Output HIGH voltage
Symbol
V
CC
I
IDLE
I
CC
V
IL
V
IH
V
OL
V
OH
---
---
---
+4.5V <= V
CC
<= +5.5V
+4.5V <= V
CC
<= +5.5V
V
CC
= +4.5V
V
CC
= +4.5V
Test
Conditions
4.5
---
---
---
2.0
---
V
CC
- 0.7
Specification
Min.
Typ.
5.0
10
100
---
---
---
---
Max.
5.5
---
200
0.8
---
0.6
---
Unit
V
mA
mA
V
V
V
V
Absolute Maximum Ratings
Condition
Operating Temperature
Storage Temperature
Supply Voltage (V
cc
)
Ground Voltage (V
ss
)
Voltage on any pin with respect to V
ss
Value
-40ºC to +85ºC
-55ºC to +125ºC
+4.5V to +5.5V
0V
-0.3V to +7.0V
NOTICE:
Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage
to the device. This is a stress rating only and functional operation of the device at those or any other
conditions above those indicated in the operation listings of this specification is not implied. Exposure to
maximum rating conditions for extended periods may affect device reliability.
RFID Technology Overview
Material in this section is based on information provided by the RFID Journal (www.rfidjournal.com).
Radio Frequency Identification (RFID) is a generic term for non-contacting technologies that use radio
waves to automatically identify people or objects. There are several methods of identification, but the
most common is to store a unique serial number that identifies a person or object on a microchip that is
attached to an antenna. The combined antenna and microchip are called an "RFID transponder" or "RFID
tag" and work in combination with an "RFID reader" (sometimes called an "RFID interrogator").
An RFID system consists of a reader and one or more tags. The reader's antenna is used to transmit
radio frequency (RF) energy. Depending on the tag type, the energy is "harvested" by the tag's antenna
and used to power up the internal circuitry of the tag. The tag will then modulate the electromagnetic
waves generated by the reader in order to transmit its data back to the reader. The reader receives the
modulated waves and converts them into digital data.
There are two major types of tag technologies. "Passive tags" are tags that do not contain their own
power source or transmitter. When radio waves from the reader reach the chip’s antenna, the energy is
converted by the antenna into electricity that can power up the microchip in the tag (typically via
inductive coupling). The tag is then able to send back any information stored on the tag by modulating
the reader’s electromagnetic waves. "Active tags" have their own power source and transmitter. The
power source, usually a battery, is used to run the microchip's circuitry and to broadcast a signal to a
reader. Due to the fact that passive tags do not have their own transmitter and must reflect their signal
Copyright © Parallax Inc.
RFID Card Reader Serial & USB (#28140 / 28340)
v2.2 3/22/2010 Page 5 of 11
