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Raspberry Pi add-on offers dead reckoning GNSS with RTK support

Jul 15, 2020 — by Eric Brown 4,959 views

SparkFun’s “GPS-RTK pHAT” for the Raspberry Pi features u-blox’s 184-channel ZED-F9R module for ADR of up to 4x concurrent GPS, GLONASS, Galileo, and BeiDou links with 20cm accuracy when linked to an RTK base station.

SparkFun has launched a $250 Raspberry Pi add-on board for “highly accurate and continuous position” in automotive, robotic rover, and other unmanned vehicle applications, including asset tracking. The GPS-RTK Dead Reckoning pHAT for Raspberry Pi showcases u-blox’s 184-channel ZED-F9R GNSS receiver module, which supports up to 4x concurrent location signals from sources including BeiDou, Galileo, GLONASS, GPS, and QZSS. Sparkfun also announced a $160 Raspberry Pi 4 Hardware Starter Kit 4GB (see farther below).

GPS-RTK pHAT, front and back
(click images to enlarge)

The new ZED-F9R module supplies the pHAT with Automotive Dead Reckoning (ADR) technology for more accurate, continuous positioning with real-time positioning rates of up to 30Hz. U-blox’s ZED-F9R module can receive both L1C/A and L2C bands

To achieve the touted 20cm horizontal positioning accuracy, the Raspberry Pi needs to be connected to an RTK (real time kinematic) equipped navigation base station. The ZED-F9R module and pHAT supports ADR and RTK with the help of a built-in 3D IMU sensor, wheel ticks, a vehicle dynamics model, correction data, and GNSS measurements.


The GPS-RTK pHAT is especially suited for “dense cities or covered areas.” Even under poor signal conditions, “continuous positioning is provided in urban environments and is also available during complete signal loss (e.g. short tunnels and parking garages),” says Sparkfun.

GPS-RTK pHAT and specs
(click images to enlarge)

The open-spec ZED-F9R GPS pHAT is available for any 40-pin Raspberry Pi, as well as other boards and systems with RPi-compatible GPIO. Like Sparkfun’s Auto pHAT robotics motor/servo and 2.3-inch Top pHAT display pHATs, the ZED-F9R GPS pHAT is said to specifically support the Raspberry Pi and two AI-enabled boards: Nvidia’s Jetson Nano Dev Board and Google’s Coral Dev Board.

Sparkfun also announced a very similar, $290 SparkFun GPS-RTK Dead Reckoning Breakout model without the RPi compatibility. Whereas the pHAT includes a single Sparkfun Qwiic interface for compatibility with other Qwiic enabled devices, the larger Breakout board offers dual Qwiic connections.

We saw the products on Electronics360, which passes along a Sparkfun claim that the boards are the first to combine ADR and RTK technologies in “a single professional platform.”

The GPS-RTK pHAT connects the u-blox receiver to the Raspberry Pi’s serial UART by breaking out a few 0.1″-spaced pins from the receiver. (The Breakout model instead uses I2C.)

The pHAT includes a rechargeable battery that powers the ZED-F9R module’s RTC, thereby reducing “the time-to-first fix from a cold start (~24s) to a hot start (~2s),” says Sparkfun. There also appears to be a micro-USB port.

Sparkfun provides a GPS Python module, a hookup guide, and a GitHub hardware repo. U-blox’s ZED-F9R module can be further configured by connecting the system to a Windows-based program called u-center. Configurable settings include baud rates, update rates, geofencing, spoofing detection, external interrupts, and SBAS/D-GPS.

GPS-RTK pHAT with optional multi-band magnetic GPS antenna (left) and Raspberry Pi 4 Hardware Starter Kit 4GB
(click images to enlarge)

The ZED-F9R GPS pHAT was announced in a Sparkfun blog that also revealed the Breakout board version plus a variant of the Qwiic Pro Micro called the BoogieBoard and a $159.95 Raspberry Pi 4 Hardware Starter Kit 4GB. The Starter Kit includes the 4GB RPi 4 along with aluminum heatsink case, power adapter, breadboard, cables, jumper wires, GPIO headers, 64GB microSD card, and more.

ZED-F9R GPS pHAT YouTube overview, complete with outtakes

Further information

The GPS-RTK Dead Reckoning pHAT for Raspberry Pi is available for $249.95 plus a GPS antenna. The antennas range in price from $3.95 for a Molex U.FL GNSS antenna to $64.95 for a multi-band magnetic mount antenna, which appears to be mounted to the top of the car in the image above. More information may be found on Sparkfun’s product and shopping page.


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