599 Menlo Drive, Suite 100
Rocklin, California 95765, USA
Office:
(916) 624-8333
Fax:
(916) 624-8003
General:
info@parallax.com
Technical:
support@parallax.com
Web Site:
www.parallax.com
Educational:
www.stampsinclass.com
RFID Reader Module (#28140)
RFID 54 mm x 85 mm Rectangle Tag (#28141)
RFID 50 mm Round Tag (#28142)
2.45” (62.2mm)
2.15” (54.5mm)
idea studio
0.14” (3.6mm)
VCC
/ENABLE
SOUT
GND
0.1” (2.5mm)
Introduction
Designed in cooperation with Grand Idea Studio (http://www.grandideastudio.com/), the Parallax Radio
Frequency Identification (RFID) Reader Module is the first low-cost solution to read passive RFID
transponder tags up to 1¾” - 3” inches away depending on the tag (see list below). The RFID Reader
Module can be used in a wide variety of hobbyist and commercial applications, including access control,
automatic identification, robotics navigation, inventory tracking, payment systems, and car
immobilization.
Fully-integrated, low-cost method of reading passive RFID transponder tags
Single-wire, 2400 baud Serial TTL interface to PC, BASIC Stamp
®
and other processors
Requires single +5VDC supply
Bi-color LED for visual indication of activity
0.100” pin spacing for easy prototyping and integration
Parallax, Inc. • RFID Reader Module (#28140) •Updated 02/2006 v1.2
3.25” (82.5mm)
2.95” (75mm)
Page 1
The Parallax RFID Reader Module works exclusively with the EM Microelectronics-Marin SA EM4100-family
of passive read-only transponder tags. A variety of different tag types and styles exist with the most
popular made available from Parallax. Each transponder tag contains a unique identifier (one of 2
40
, or
1,099,511,627,776, possible combinations) that is read by the RFID Reader Module and transmitted to
the host via a simple serial interface.
Electronic Connections
The Parallax RFID Reader Module can be integrated into any design using only four connections (VCC,
/ENABLE, SOUT, GND). Use the following circuit for connecting the Parallax RFID Reader Module to the
BASIC Stamp microcontroller:
Pin
1
2
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.
3
SOUT
O
Serial Out. TTL-level interface, 2400bps, 8 data bits, no parity, 1 stop bit.
4
GND
G
System ground. Connect to power supply’s ground (GND) terminal.
Note: Type: I = Input, O = Output, P = Power, G = Ground
Pin Name
VCC
/ENABLE
Type
P
I
Parallax, Inc. • RFID Reader Module (#28140) •Updated 02/2006 v1.1
Page 2
Communication Protocol
Implementation and usage of the RFID Reader Module is straightforward. BASIC Stamp 1, 2, and
SX28AC/DP code examples (SX/B) are included at the end of this documentation.
The RFID Reader Module is controlled with a single TTL-level active-low /ENABLE pin. When the /ENABLE
pin is pulled LOW, the module will enter its active state and enable the antenna to interrogate for tags.
The current consumption of the module will increase dramatically when the module is active.
A visual indication of the state of the RFID Reader Module 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 and the antenna is transmitting, the LED will be RED.
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 focused). If the tag is held sideways (perpendicular to the antenna) you'll either
get no reading or a poor reading. 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 confuse the reader. The two tags
available in the Parallax store have a read distance of approximately 3 inches. Actual distance may vary
slightly depending on the size of the transponder tag and environmental conditions of the application.
When a valid RFID transponder tag is placed within range of the activated reader, the unique ID will be
transmitted as a 12-byte ASCII string via the TTL-level SOUT (Serial Output) pin in the following format:
MSB
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
LSB
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 a line feed and carriage return characters, respectively). The middle ten bytes
are the actual tag's unique ID.
All communication is 8 data bits, no parity, 1 stop bit, non-inverted, least significant bit first (8N1). The
baud rate is configured for 2400bps, a standard communications speed supported by most any
microprocessor or PC, and cannot be changed. The Parallax RFID Reader Module initiates all
communication. The Parallax RFID Reader Module can connect directly to any TTL-compatible UART or to
an RS232-compatible interface by using an external level shifter.
Absolute Maximum Ratings and Electrical Characteristics
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
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.
Parallax, Inc. • RFID Reader Module (#28140) •Updated 02/2006 v1.1
Page 3
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
Test
Conditions
---
---
---
+4.5V <= V
CC
<= +5.5V
+4.5V <= V
CC
<= +5.5V
V
CC
= +4.5V
V
CC
= +4.5V
Specification
Min.
Typ.
Max.
4.5
5.0
5.5
---
10
---
---
90
---
---
---
0.8
2.0
---
---
---
---
0.6
V
CC
- 0.7
---
---
Unit
V
mA
mA
V
V
V
V
RFID Tags Available From Parallax
Parallax provides two passive RFID tags from our on-line store. We’re stocking the tags because many
suppliers have high minimums, yet many of our customers may only want a few tags for their basic
experimentation.
54 mm x 85 mm Rectangle Tag (#28141)
50 mm Round Tag (#28142)
1.97” (50mm)
Ø.17” (4.3mm)
hole
orld
T
W
nd
po
s
Page 4
0.8” (2.1mm) thick
Actual tag dimensions may vary. Contact Parallax for specific information.
Parallax, Inc. • RFID Reader Module (#28140) •Updated 02/2006 v1.1
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Optional Tag Information
Even though Parallax only carries a Round Tag and a Rectangle Tag the following values were obtained
from different tags available in the market.
ISO Card:
World Tag 50mm:
World Tag 30mm:
Bobsleigh Keyfob:
Tear shape:
Wristband:
6.3cm
6.8cm
5.3cm
5.3cm
4.0cm
4.0cm
(2.5") +/-
(2.7") +/-
(2.1") +/-
(2.1") +/-
(1.6") +/-
(1.6") +/-
10%
10%
10%
10%
10%
10%
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. In the case of the Parallax RFID Reader Module,
correctly received digital data is sent serially through the SOUT pin.
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 (known as "parasitic
power"). The tag is then able to send back any information stored on the tag by reflecting the
electromagnetic waves as described above. "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
to the reader, the reading distance is much shorter than with active tags. However, active tags are
typically larger, more expensive, and require occasional service. The RFID Reader Module is designed
specifically for low-frequency (125 kHz) passive tags.
Frequency refers to the size of the radio waves used to communicate between the RFID system
components. Just as you tune your radio to different frequencies in order to hear different radio stations,
RFID tags and readers have to be tuned to the same frequency in order to communicate effectively. RFID
systems typically use one of the following frequency ranges: low frequency (or LF, around 125 kHz), high
frequency (or HF, around 13.56 MHz), ultra-high frequency (or UHF, around 868 and 928 MHz), or
microwave (around 2.45 and 5.8 GHz). It is generally safe to assume that a higher frequency equates to
a faster data transfer rate and longer read ranges, but also more sensitivity to environmental factors such
as liquid and metal that can interfere with radio waves.
There really is no such thing as a "typical" RFID tag. The read range of a tag ultimately depends on many
factors: the frequency of RFID system operation, the power of the reader, and interference from other RF
devices. Balancing a number of engineering trade-offs (antenna size v. reading distance v. power v.
Parallax, Inc. • RFID Reader Module (#28140) •Updated 02/2006 v1.1
Page 5
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