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RXM-SG GPS Module w/Ext Antenna (#28505)
The RXM-SG GPS Module provides a high quality, highly sensitive GPS receiver with an external antenna
to provide a complete GPS solution for both microcontroller and PC applications. The high-performance
SiRFstar III chipset features 20 parallel satellite tracking channels for fast acquisition of NMEA0183 data
for robotics navigation, telemetry or experimentation. This GPS Module can connect to a microcontroller
or even a PC (via USB). A Windows application provides a graphical display of the GPS data and can
even show your location on Google Maps (internet connection required). Four general purpose I/O pins
provide expansion for pin-intensive projects.
Features
SiRFstar III chipset
Outputs raw NMEA0183 data strings to microcontroller
View data graphically on your PC via USB connection
200,000+ correlations
Low power consumption
High sensitivity (-159 dBm)
20 satellite tracking channels
Battery-backed SRAM
11-pin SIP header with breadboard-friendly 0.1” spacing
Key Specifications
Power Requirements: 5 V @ ~50 mA (typical)
Communication: 3.3 V CMOS asynchronous serial @ 9600
baud default for microcontrollers, or USB for PC
Dimensions: 1.7 x 1.6 x 0.6 in (4.33 x 4.09 x 1.52 cm)
Operating temperature: -22 to +185 °F (-30 to +85 °C)
Application Ideas
RoboMagellan robot competition
Fleet Management
Positioning and Navigation
Surveying
Packing List
RXM-SG GPS Module
2 shorting blocks (pre-installed)
1575.42 MHz external GPS antenna with 9' cable
3 V Lithium battery (CR2032)
Copyright © Parallax Inc.
RXM-SG GPS Module w/Ext Antenna (#28505)
v1.0 8/27/2010 Page 1 of 6
Quick-Start Guide
Install the battery on the module: slide the battery under the clip on the back, from the top,
ensuring that the + symbol faces away from the PCB.
Connect the External GPS Antenna to its MMCX connector as shown in Figure 1.
For PC Connection via USB
Install the USB drivers (required) and the LINX MDEV-GPS software (optional) from the links in
the Resources and Downloads section on page 5.
Make sure the jumper block is in the Shprted position, as shown Figure 3.
Then, connect the GPS Module to your PC with a USB A to Mini B cable (not included) as shown
in Figure 1. Your GPS module is now ready to use with the software of your choice via the USB
port.
For Microcontrollers
Make sure the jumper block is in the Open position, as shown in Figure 2.
Connect the GPS module’s GND pin to ground, and +5V pin to regulated 5 VDC.
Minimum I/O connection is to connect the GPS module’s TX pin to your microcontroller’s available
I/O pin set to input. Read the Communication Protocol section on page 3 before interfacing a 5 V
microcontroller to the GPS module’s RX or other input pins. For BASIC Stamp and Propeller
microcontroller examples, see page 6.
Figure 1: Module Connections
Figure 2: Jumpers Open—Microcontroller Mode
Figure 3: Jumpers Shorted—USB to PC Mode
Copyright © Parallax Inc.
RXM-SG GPS Module w/Ext Antenna (#28505)
v1.0 8/27/2010 Page 2 of 6
Theory of Operation
Global Positioning System (GPS) is a space-based global navigation system providing location and time
information anywhere on or near the earth. The system was created by the United States Department of
Defense and consists of 24 satellites orbiting the earth. With an unobstructed view of the sky the GPS
system will attempt to acquire and lock on to three or more satellites to provide a position fix using
trilateration. Time information is provided by atomic clocks aboard each satellite. This information is
provided to the user in UTC format.
Device Information
Supplying Power
The RXM-SG GPS module includes one 3 V lithium CR2031 battery. This battery is necessary for the
module to operate. The purpose of the battery is to provide a backup power supply for the SRAM and
RTC only; it is not sufficient on its own to power the module for operation. There are two power options:
When using a PC connection via USB, the module draws power from the USB port for operation.
When using a microcontroller connection, the module requires 50 mA of 5 V regulated DC voltage
on its +5V pin (and a ground connection on GND).
CAUTION:
Do not apply voltage to the module’s +5 V pin while the module is connected to the PC via
USB, as this could damage your computer’s USB port.
Jumper Block
The purpose of the jumper block is to prevent write contention to the GPS module’s TX and ON_OFF
lines. The jumper block should always be in the Open position when used with a microcontroller, and in
the Shorted position when used with a PC via USB. However, it is possible to receive data from the
module by either method with the jumper block in either position.
LEDs
There are three surface-mount LEDs on the GPS module:
Red (leftmost): Transmitting data to PC via USB
Blue (center): Receiving data from PC via USB
Green (rightmost): GPS channel lock status. This LED will blink rapidly while acquiring satellites
signals until three channels have locked onto satellites. Once three channels are locked, the
blinking will slow to a once-per-second rate.
Communication Protocol
Communication with the RXM-SG GPS Module is via non-inverted, 3.3 V CMOS level serial protocol at a
default baud rate of 9600 bps. The baud rate can be set via command to 4800, 9600, 19200, 38400 or
57600 bps via the SetSerialPort command (see datasheet). Note that the GPS is compatible with 5 V
microcontrollers from the perspective of the GPS output. Any signals going into the GPS module would
need to be buffered using a level translator or buffer chip such as the 74LVC244A (Parallax #603-10004).
Command Set
The commands understood by the GPS Module are covered in detail in the RXM-GPS-SG datasheet.
These commands are structured to look very much like the NMEA data the GPS provides. Note that each
command must have a valid checksum at the end for the module to understand the command and
process it. If you are unfamiliar with how the checksums are constructed please see the RXM-GPS-SG
datasheet under the section, interfacing with NMEA messages.
Copyright © Parallax Inc.
RXM-SG GPS Module w/Ext Antenna (#28505)
v1.0 8/27/2010 Page 3 of 6
Calibration
GPS calibration is not necessary as the GPS Module will download the necessary data from the available
satellites automatically, however when the GPS Module is first powered up it must acquire ephemeral
data from the satellites, which can take several minutes. Accuracy improves as more satellites are
acquired, however civilian GPS resolution is around 20 yards (65 feet).
Please see the RXM-GPS-SG datasheet for additional information.
Pin Definitions
Pin
1
2
3
4
5
6
7
8
9
10
11
Name
GND
+5V
RX
TX
RFPWRUP
ON_OFF
N/C
GPIO01
GPIO14
GPIO15
GPIO13
Type Function
G
P
I
O
O
I
—
I/O
I/O
I/O
I/O
Ground (0 V)
Power (5 V)
GPS Receive*
GPS Transmit
Power State Indication
Edge Triggered soft on/off request*
No Connection
General Purpose I/O*
General Purpose I/O*
General Purpose I/O*
General Purpose I/O*
Pin Type: P = Power, G = Ground, I = Input, O = Output
*see RXM-GPS-SG datasheet for pin ratings and details
Precautions
Always be sure to check the position of the jumpers when switching between Microcontroller and
PC interfaces. The jumpers should be OPEN for Microcontrollers and CLOSED (shorted) for PC
interfacing through a USB port.
The I/O pins operate at a 3.3 V CMOS level and are not 5 V tolerant. Because of this, 5 V
microcontrollers, such as the BASIC Stamp series, cannot send commands to the GPS Module
directly, however they can receive NMEA data without issue. Any signals going into the GPS
module would need to be buffered using a level translator or buffer chip such as the 74LVC244A
(Parallax #603-10004).
Do not connect the RXM-SG GPS Module to a USB port and external power at the same time.
Do not connect the RX, TX, RFPWRUP or ON_OFF pins while interfacing to the USB port.
Copyright © Parallax Inc.
RXM-SG GPS Module w/Ext Antenna (#28505)
v1.0 8/27/2010 Page 4 of 6
Module Dimensions
Resources and Downloads
Check for the latest version of this document, free software, and example programs from the RXM-GS
GPS Module product page. Go to www.parallax.com and search 28505.
Product Page Resources
Example code for the BASIC Stamp 2p.
Linx Technology’s GPS Module Evaluation software for Windows.
RXM-GS GPS Module Schematic
GPIO Command Set PDF
You may also visit
http://www.parallax.com/go/gps
for a GPS Module comparison chart.
USB Drivers
Before connecting this device to a PC you must first install the USB Drivers. Windows 2000/XP/Vista/7
drivers can be found at the following URL:
http://www.parallax.com/usbdrivers
If you wish to connect your GPS Module to a Mac or a PC running Linux you must obtain other drivers
available at the following URL: http://www.ftdichip.com/Drivers/VCP.htm
Parallax Inc. cannot support installation or use of the GPS Module with drivers other than the Windows
drivers posted on the Parallax website via the link above.
Propeller Example Code
The Propeller Object Exchange is a resource for Propeller objects created by Parallax Inc. as well as those
submitted by other Propeller chip users. A search for GPS on the OBEX yields several available GPS
objects which are free to download and use. You can visit the object exchange at the following URL:
http://obex.parallax.com/
Copyright © Parallax Inc.
RXM-SG GPS Module w/Ext Antenna (#28505)
v1.0 8/27/2010 Page 5 of 6
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