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Output to an Embedded System

Many applications using the RTK products will use a 3rd party GIS application or mobile app like SW Maps and receive the data over Bluetooth. For RTK devices that have an external connection, a user can obtain the NMEA data over serial directly.

USB

Torch: Feature Supported / EVK: Feature Supported

Most SparkFun RTK devices have a USB port for programming and status reports. This USB port can also be configured to output full NMEA/RTCM output that can be used to create a wired connection to an embedded system. See Output GNSS Data over USB for more information.

DATA Port

Torch: Feature Not Supported / EVK: Feature Supported

For this example, we will connect the output from the DATA port of an RTK Facet to a USB to Serial adapter so that we can view the serial data over a terminal connection.

The DATA port on the RTK Facet can be configured to output a variety of different signals including NMEA Serial data. Be sure to check out the Ports Menu section to be sure your device is configured to output NMEA.

Connect the included 4-pin JST to breadboard cable to the DATA port. The cable has the following pinout:

  • Red - 3.3V
  • Green - TX (output from the RTK device)
  • Orange - RX (input into the RTK device)
  • Black - GND

Wires connected to a SparkFun USB C to Serial adapter

Open a terminal at 115200bps and you should see NMEA sentences:

NMEA output from the RTK Surveyor

The Data connector on all RTK products is a 4-pin locking 1.25mm JST SMD connector (part#: SM04B-GHS-TB, mating connector part#: GHR-04V-S). 3.3V is provided by this connector to power a remote device if needed. While the port is capable of sourcing up to 600mA, we do not recommend more than 300mA. This port should not be connected to a power source, so if your embedded device has its own power do not connect the red wire.

Warning! All data in and out of RTK products is 3.3V. Exposing these pins to 5V or higher voltage logic will damage the device.

The parsing of NMEA sentences is straightforward and left to the reader. There are ample NMEA parsing libraries available in C++, Arduino, Python, and many more languages.

External Terminals

Torch: Feature Not Supported / EVK: Feature Supported

On devices that support it, external screw terminals provide direct access to the GNSS TX and RX signals via the 3.5mm screw terminal I/O header:

Reference Station I/O screw terminals

  • TX2 : u-blox ZED-F9P UART2 transmit: 3.3V OUTPUT

  • RX2 : u-blox ZED-F9P UART2 receive: 3.3V INPUT

Please see the EVK Hookup Guide for more details.