MAX-7Q GNSS HAT

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MAX-7Q GNSS HAT
MAX-7Q-GNSS-HAT-1.jpg

GNSS Module, u-blox MAX-7Q onboard
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Positioning Principle

What's GNSS

GNSS (Global Navigation Satellite System) is a general term for multiple satellite systems. At present, there are BDS (China), GLONASS (Russia), GPS (United States), Galileo (Europe), QZSS (Japan) and IRNSS (India) navigation satellite systems in the world. The features of GNSS are as follows:

  • GPS is widely used with mature technology, and the frequency band signals such as L1C/A, L2C and L5, have improved the positioning accuracy.
  • GNSS modules with multi-system and multi-band can capture satellites from different satellite systems, which greatly increases the number of effective satellites and improves positioning accuracy and stability.
  • The signal received by the GNSS module contains reflected and refracted signals, resulting in multi-path effects that affect the positioning accuracy. The multi-band and multi-constellation system technology can effectively lessen errors caused by the atmosphere and improve positioning accuracy.
  • With the development of GNSS, a variety of positioning technologies such as RTK, PPP-RTK and multi-sensor fusion positioning DR (Dead Reckoning) have emerged to meet the needs of differentiated high-precision positioning.

GPS Principle

In this section, the working principle of GPS receiver positioning is shown in the figure below, and the details are described in the following 5 points. For details of the positioning principle, please refer to GPS Positioning Principle, GPS Operation Principle, Fundamentals of gps receivers and FUNDAMENTALS OF GPS.

  • GPS satellites continuously send radio signals with their own time and position information in the air for GPS receivers (GNSS modules such as ZED-F9P)
  • A pseudo-random code will be generated inside the satellite and the receiver. Once the two pseudo-random codes are synchronized, the receiver can measure the difference between the time the radio signal is transmitted and the time it arrives at the receiver (referred to as the time delay), and multiply the time delay by the speed of light to get the distance (pseudorange).
  • The time of the GPS system is maintained by the rubidium atomic frequency standard of the atomic clocks on each satellite. These satellite clocks are generally accurate to within a few nanoseconds of Coordinated Universal Time (UTC), which is maintained by the Naval Observatory's "Master Clock", the stability of each master clock is several 10^(-13) seconds.
  • Computers and navigation information generators on GPS satellites know precisely their orbital positions and system time, while a global network of monitoring stations keeps track of satellites' orbital positions and system time. The main control station at Schriever Air Force Base in Colorado, together with its operation and control section, input the orbital position and onboard clock correction data calculated on the basis of complex models into each GPS satellite at least once a day.
  • To calculate the 3D position of the GPS receiver (GNSS module), the GPS receiver is required to receive signals from at least four satellites, and the 3D position is calculated according to the space triangle Pythagorean theorem and the quadratic linear equation.

GPS.png

What's RTK

RTK (Real Time Kinematic), also known as carrier phase differential technology, is a GNSS positioning technology that supports centimeter-level positioning accuracy (referred to as RTK) and is a differential method for real-time processing of the carrier phase observations of two measuring stations. The working process of RTK is shown in the figure below. The DGPS corrections generated by the base station (GNSS receiver) are transmitted to the mobile station (GNSS receiver) in real-time through the mobile network for calculation and centimeter positioning.

RTK.png

RTK Application

  • Apply in various control surveys such as traditional geodetic surveys and engineering control surveys in triangulation and wire netting methods, and use RTK to measure the positioning accuracy in real-time to ensure observation quality and improve operational efficiency. Compared with non-real-time measurements such as normal GPS static surveys, fast static surveys, and pseudo-dynamic surveys, it must be retested when the accuracy does not meet the requirements. In addition, RTK is used in highway control measurement, electronic circuit control measurement, water conservancy engineering control measurement, and geodetic survey, which can reduce labor intensity, save costs, and complete control point measurement within minutes or even seconds.
  • Topographic mapping: Using RTK only requires one person with the instrument to stay at the detail point for a second or two, and input the feature code at the same time. The accuracy of points and areas can be known in real-time through the handbook. After returning to the room, the professional software interface can output the required topographic map. In this way, RTK only requires one person to operate, and it does not require point-to-point vision, which greatly improves efficiency. With RTK and the electronic handbook, you can measure and design various topographic maps, such as general surveying, railway strip topographic maps, highway pipeline topographical maps, reservoir topographic maps, nautical ocean surveying, and so on with the depth sounder.
  • Setting out is an application branch of measurement. When using RTK to set out, you only need to input the designed point coordinates into the electronic handbook with the GPS receiver on your back, and it will remind you to go to the position. It is not only fast and easy but also is high-accuracy and uniform as GPS is set out by coordinates directly. Hence, the efficiency of setting out in exterior operation is greatly improved, and only one person to operate.

Dimension

GNSS Principle section.jpg

Test it in Windows PC

1. Download and install u-center software and then open it
2. Set the jumpers at A area, assemble the GNSS antenna, and set the receiver of the antenna on open-area outside. Connect the micro USB interface to PC
3. Note that you should set the side without sticker upward, Open Device Manager and check the COM port, connect MAX-7Q, and use auto-baudrate
4. Power the MAX-7Q module and set it to 3D mode, select File ->Database Export ->Google Map Html to export file
5. Download Test file and open it by Chrome browser, import the file which is saved with u-center above to check position information.
6. Please refer to the User guide about how to use the u-center.
MAX-M8Q GNSS HAT 002.jpg MAX-M8Q GNSS HAT 003.jpg MAX-M8Q GNSS HAT 005.jpg MAX-M8Q GNSS HAT 004.jpg

Use it in RaspberryPi

Hardware Connection

MAX-M8Q GNSS HAT 007.jpg

PIN Raspberry Pi(BCM) Raspberry Pi(WiringPi) Descruption
5V - - 5V Power input
GND - - Ground
RXD P14 P15 Receiver pin of UART
TXD P15 P16 Transmit pin of UART
SDA P2 P8 SDA pin of I2C
SCL P3 P9 SCL pin of I2C
PPS P18 P1 PPS pin of module
INT P27 P2 Wakeup pin, low active

Enable Serial Port

Open the Raspberry Pi Terminal and configure by commands 

sudo raspi-config
#Choose Interfacing Options -> Serial, close shell visit, and enable hardware serial port
sudo reboot

L76X GPS Module rpi serial.png

Install libraries and configure

  • Install Python libraries
sudo apt-get update
sudo apt-get install gpsd gpsd-clients 
sudo pip3 install gps3
  • Configure gpsd
#Open gpsd file
sudo nano /etc/default/gpsd
#Change the below codes of file and save
USBAUTO="false"
DEVICES="/dev/ttyS0"
GPSD_OPTIONS="/dev/ttyUSB0"
  • Download demo codes
mkdir ~/Documents/MAX-XXX_GNSS_HAT_Code
cd ~/Documents/MAX-XXX_GNSS_HAT_Code/
wget https://files.waveshare.com/upload/0/0f/MAX-XXX_GNSS_HAT_Code.zip
unzip MAX-XXX_GNSS_HAT_Code.zip

Python Example

Enter the Python directory (demo codes), and run the example. 

cd ~/Documents/MAX-XXX_GNSS_HAT_Code/RaspberryPi/python/coordinate_converter
sudo python3 main.py

MAX-M8Q GNSS HAT 006.jpg

NTP Server

The system clock of drivers like personal compute or server always has calibration issues as the figure below. In high-frequency trading systems, this issue affects High-precision clock requirement applications like automated production lines, etc. The NEO-M8T's enhanced sensitivity and concurrent constellation reception extend coverage and integrity to challenging signal environments. It uses the atomic clocks of the satellite to get rid of the included network and other factors. Here we use NEO-M8T and Raspberry Pi to build an NTP server and provide a clock for the WLAN network indoors. NEO-M8T GNSS TIMING HAT 002.jpg
1. Connect the antenna to NEO-M8T GNSS TIMING HAT, and set the receiver close to the windows.
2. Connect the NEO-M8T to Raspberry Pi, Power it on, and wait for the PPS signal.
3. Open a terminal and run the following commands.

sudo apt-get install git
cd ~/Documents
sudo git clone https://github.com/beta-tester/RPi-GPS-PPS-StratumOne.git
cd RPi-GPS-PPS-StratumOne
sudo chmod 777 install-gps-pps.sh

4. Reboot Raspberry Pi after installing it.
5. Open and modify /boot/config.txt file, change the gpiopin=4 to gpiopin=18 of the last line and save it. 

sudo nano /boot/config.txt
dtoverlay=pps-gpio,gpiopin=18,capture_clear  # /dev/pps0

6. Test pps0 by the following command. And now the Raspberry Pi uses the time of NEO-M8T.

watch -n1 chronyc sourcestats -v

NEO-M8T GNSS TIMING HAT 006.jpg
7. To provide time for other devices, you can access it by the IP address of Raspberry Pi like:192.168.6.93
NEO-M8T GNSS TIMING HAT 005.jpg
8. You can check the time by the following command on a Linux device. 

sudo apt install ntpdate
sudo ntpdate 192.168.6.93

Use it in STM32 Board

Hardware Connection

MAX-M8Q GNSS HAT 008.jpg

GNSS Module XNUCLEO-F103RB Description
5V - 5V Power input
GND GND Ground
RXD P9(TX) Receive pin of UART
TXD P10(RX) Transmit pin of UART

Run the example

Download the demo codes. Open the STM32 project with Keil software, compile and download it to the XNUCLEO-F103RB board, connect UART2 pins to the PC, and check the information with COM assistance software.
MAX-M8Q GNSS HAT 009.jpg

Working with Jetson Nano

  • Install the Python library
sudo apt-get update
sudo apt-get install python-serial
sudo apt-get install gpsd gpsd-clients python-gps
sudo pip3 install gps3
  • Modify gpsd parameters

Open the gpsd file on the terminal 

sudo nano /etc/default/gpsd

Modify the following parameters of the gpsd file, then save and exit the file. 

USBAUTO="false"
DEVICES="/dev/ttyTHS1"
GPSD_OPTIONS="/dev/ttyUSB0"

+Download the demo 

mkdir ~/Documents/MAX-XXX_GNSS_HAT_Code
cd ~/Documents/MAX-XXX_GNSS_HAT_Code/
wget https://files.waveshare.com/upload/0/0f/MAX-XXX_GNSS_HAT_Code.zip
unzip MAX-XXX_GNSS_HAT_Code.zip
  • Check the port for data
sudo chmod 777 /dev/ttyTHS1
sudo minicom -D /dev/ttyTHS1 -b 9600
sudo cat /dev/ttyTHS1
sudo gpsd /dev/ttyTHS1 -F /var/run/gpsd.sock
sudo cgps -s
sudo killall gpsd
sudo reboot

python

Enter the Python directory and run the demo, and you can view the information directly on Google Maps. 

cd ~/Documents/MAX-XXX_GNSS_HAT_Code/RaspberryPi/python/coordinate_converter
sudo python3 main.py

MAX-M8Q GNSS HAT 016.jpg

Resource

Documents

Demo codes

Software

Datasheet

Support



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