SparkFun RTK Express Plus

The SparkFun RTK Express Plus is an easy to use GNSS receiver for centimeter-level positioning. Perfect for surveying, autonomous vehicles, logging, and all types of post processing, this preprogrammed device can also be used for autonomous driving, navigation, asset tracking and any other application where there is a clear view of the sky. The RTK Express Plus adds an internal IMU to combine real-time GNSS tracking with advanced sensor fusion. The result is accurate positioning even when GNSS is lost in tunnels, parking garages, etc. Out of the box an RTK Express Plus can be used with a correction source to create an RTK system capable of 14mm horizontal positional accuracy. The built-in Bluetooth® connection via an ESP32 WROOM enables the user to use the RTK Express Plus with their choice of GIS application on a phone or tablet. The built in battery allows for over five hours of field use and is compatible with common USB battery banks.

We took all the lessons from the RTK Surveyor and built the RTK Express Plus. The RTK Express Plus is built upon the ZED-F9R u-blox receiver which uses the same F9 engine as all our RTK products but couples it with a built-in IMU. The embedded display allows for immediate feedback of horizontal positional accuracy, satellites in view, logging status, sensor fusion status, battery level, Bluetooth® MAC, etc. The rocker switches found on the original have been replaced by keypad buttons. Sparkfun increased the battery to 1300mAh for a longer run time. The internal switches have been replaced by a digital mux allowing for some really exciting applications including event triangulation. More ESD protection was added to protect the RF path, and Sparkfun even threw in an accelerometer for digital leveling in the field. Please note u-blox's sensor fusion algorithms are designed specifically for vehicles and will not aid in the accuracy of normal surveying.

This device can be used in two modes:

• GNSS Positioning (~30cm accuracy)
• GNSS Positioning with RTK (1.4cm accuracy)

In Position mode the device receives L1/L2 signals from a user-provided antenna and the high-grade GNSS receiver provides lat/long and altitude with accuracies around 300mm. If enabled in automotive applications, the internal IMU augments the position information when GNSS reception is degraded.

In Positioning with RTK mode the device receives L1/L2 signals from the antenna and correction data from a base station. The correction data can be obtained from a cellular link to online correction sources or over a radio link to a RTK Surveyor/Express setup as a base station. If enabled in automotive applications, the internal IMU augments the position information when GNSS reception is degraded.

Two cables are provided with the RTK Express Plus allowing a user to plug in our easy to use Serial Telemetry Radios or their own radio link. If a local correction source is within 10km, a user can also use their phone to provide correction data over the Bluetooth® link (no external radio needed!).

Note: The SparkFun RTK Express Plus is just the enclosed device and does NOT include an antenna, serial telemetry radio, or associated mounting pieces. These items will need to be purchased separately from the Hookup Accessories below.

GNSS Receiver: ZED-F9R

• Concurrent reception of GPS, GLONASS, Galileo and BeiDou
• Receives both L1C/A and L2C bands
• Built-in IMU (triple axis accel, triple axis gyro)
• Current: 68mA - 130mA (varies with constellations and tracking state)
• Time to First Fix: 25s (cold), 2s (hot)
• Max Navigation Rate:
  • PVT (basic location over UBX binary protocol) - 25Hz
  • RTK - 20Hz
  • Raw - 25Hz
• Horizontal Position Accuracy:
  • 2.5m without RTK
  • 0.010m with RTK
• Max Altitude: 50km (31 miles)
• Max Velocity: 500m/s (1118mph)

Bluetooth® Transceiver: ESP32 WROOM

• Xtensa® dual-core 32-bit LX6 microprocessor
• Up to 240MHz clock frequency
• 16MB of flash storage
• 520kB internal SRAM
• Integrated 802.11 BGN WiFi transceiver
• Integrated dual-mode Bluetooth® (classic and BLE)
• Hardware accelerated encryption (AES, SHA2, ECC, RSA-4096)
• 2.5 µA deep sleep current

Overall Device

• Internal Battery: LiPo 1300mAh with 500mA charging
• Radio Port: 3.3V TTL Serial (57600bps RTCM TX/RX)
• Data Port: 3.3V TTL Serial (460800bps NMEA)
• Embedded OLED Display for available satellites, data logging, and more.
• Push button controls
• Weight: 162g (entire device including battery)
• Dimensions: 132mm x 101mm x 32mm (5.2in x 3.9in x 1.2in)
• 1x Qwiic Connector
• 1x microSD Socket for optional logging

• Schematic
• Eagle Files
• Hookup Guide
• Firmware Repo
• Hardware Repo