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Sparkfun ZED-F9P circuit test with the Orpheon network

Sparkfun ZED-F9P circuit test with the Orpheon network

By Didier MartinezPosted

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We receive many requests concerning the operating principle of RTK corrections but also many questions about the possibilities of integrating a GPS chip to develop its own applications. What could be simpler to answer these questions than to go through the same integration steps to better understand the operating logic.

Democratization of technology

Today the integration of precision GNSS chips is democratizing by becoming affordable and makes it easy to imagine all kinds of practical uses. It then becomes possible to integrate an RTK receiver with centimetric precision in a compact, light and energy-efficient design to meet the requirements of these new applications and thus free the imagination and creativity. null

Objective of this test

Our goal here is not to promote one product over another, but just to use a module that will simplify our access to a centimeter position given the little time we can devote to this exercise. Our objective is quite minimalist since we just want to be able to connect to the Orpheon network server and obtain the corrections to display a position whose precision has been increased thanks to the network corrections.

Warnings

This test makes it possible to illustrate the stages of integration in an attempt to popularize the main lines of the content. There is no question here of worrying about performance or precision (maybe we will do that later). There is also no question of providing a turnkey solution or software or part of a program.

There are several evaluation kits on the market:

On our side we tested the Sparkfun ZED-F9P circuit because the implementation is quite simple. Ordered more than a year ago, we cannot tell you today how soon or at what price this devaluation kit is now available. To do the very first tests very quickly, it is possible to connect a PC via its USB-C port (which will power the card) and a GPS antenna, for our part we have opted for an AS10 Leica antenna available on our shelves .

  • Concurrent reception of GPS, GLONASS, Galileo and BeiDou
  • Receives both L1C/A and L2C bands
  • Voltage: 5V or 3.3V but all logic is 3.3V
  • 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)
  • Weight: 6.8g
  • Dimensions: 43.5mm x 43.2mm (1.71in x 1.7in)
  • 2x Qwiic Connectors

With the Ublox U-center application, it is very easy to view the available satellites. It still takes a bit of time and patience to become familiar with the app. Once the NTRIP Client Orpheon parameters have been entered, the GPS converges and fixes fast enough to obtain a centimetric positioning.

Connection to the Arduino board

Then, what is interesting is to make this system a little more autonomous to be able to use it at the heart of a more complex project. Then just connect this development board to the Arduino Uno 33 IOT controller. The role of the controller board will be to act as a gateway between the GPS (ublox) and the corrections server. We opted for the I2C port to be able to possibly have the other Com ports for other services (maybe not the simplest nor the most judicious … but it works)

Ease of integration

It is interesting to see that the integration of an RTK GPS module is greatly facilitated by the open source codes available on the net and very widely commented. Development boards can be driven via a serial port or I2C. It will be necessary to integrate into this Arduino RTK GPS a “Ntrip client” which is a small software module (available in open source on the internet). Whatever your hardware, the steps for connecting to an RTK server have been standardized and defined to allow everyone access to centimeter precision.

General operation

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In detail

At the time of connection, the Ntrip client identifies itself on the server and sends its initial position (NMEA frame type GGA). It uses the connection parameters:
  • Server DNS address
  • Server com port
  • User ID
  • Password
  • Mount point (allows you to define the com protocol and the RTCM messages sent by the server)
it is interesting to understand what happens at each of these stages. The server will then send the correction parameters every second that the module will have to “pass” to the GPS for its positioning calculations. Then the module will have to send its position to the server (at least every 20sec) to allow the server to evolve the correction solution and to ensure that the connection is still “alive” null

Content of the NMEA GGA frame

There are a large number of different NMEA frames (over thirty). These frames are defined by the NMEA 0183 standard which is a specification for communication between marine equipment, including GPS. This standard uses frames or sentences to transmit information, each information is separated by a comma.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
$GNGGA, 073939.00, 4841.47953, N 00212.97078, E, 1, 24, 0.62, 165.7, M, 46.2, M , , *42
The frame begins with the sign “$” then the type of epic is defined by the two characters that follow. Each frame has its own syntax, but depending on the case, they must end, after the “*” sign, with control bits which make it possible to verify that the frame has not been damaged before its reception. The NTRIP server needs the information contained in the GGA frame because this frame provides the current position of the GPS receiver. null

Conclusion :

The essence of this test was for us to go through the first steps of implementing a GNSS chip to connect it to the Orpheon server and to obtain our first positions corrected. If we want to go further, we will have to stabilize our version to ensure the reconnection of the module to the Orpheon server in the event of loss of the internet link.

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As part of tests, trials aimed at testing or validating a solution, we can provide a free trial offer for limited and temporary access to corrections from the Orphéon network. Tell us about your needs and the scope of your tests so that we can study your request.

In order to offer offers perfectly adapted to the needs of users, we have designed several subscription formulas. Our commercial offer is very clear and very flexible. So, in complete transparency, you only pay for what you really need.

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Didier Martinez