NEO-M8T GNSS TIMING HAT

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), 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, L5, have improve the positioning accuracy.
GNSS module 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 Working Principle, Fundamentals of gps receivers, 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 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 on-board 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.

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 Application

Apply in various control surveys such as traditional geodetic surveying and engineering control surveying 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 measurement such as normal GPS static surveys, fast static survey, pseudo-dynamic survey, 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, geodetic survey, which can reduce labor intensity and save costs, and can 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 point and area can be known in real time through the screen. 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 electronic handbook, you can measure and design various topographic maps, such as general surveying, railway strip topographic map, highway pipeline topographical map, can measure reservoir topographic map, 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 can operate.

Dimension

Working with windows

1. Download and install u-centersoftware, then open the u-center.
2. Set the jumpers in A area, connect the GNSS antenna, Put the receiver of the antenna in an open area outside to receive a GPS signal, and connect the Module to the PC by Micro USB cable.
3. Note that you need to set the side of the antenna without the sticker upward, check the COM port in Device Manager. Use the u-center to connect MAX-M8Q by selecting the COM port and selecting auto baud rate.
4. Enable 3D mode and export the file by selecting File -> Database Export -> Google Map Html.
5. Download Text_Release software and unzip. Open the file by Chrome, then import the HTML file which we saved above to check the position.
6. For detailed information about the u-center software, please refer to User Guide.

Working with Raspberry Pi

Hardware Connection

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

Enable UART interface

Open a terminal and run the following commands

sudo raspi-config
#Choose Interfacing Options -> Serial -> No -> Yes
sudo reboot

Libraries Installation

Install Python libraries:

sudo apt-get update
sudo apt-get install gpsd gpsd-clients 
sudo pip3 install gps3

Modify gpsd:

#Open gpsd file
sudo nano /etc/default/gpsd
#Change the lines below 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 Examples

Enter the corresponding Python directory and run the following commands:

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

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.
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

7. To provide time for other devices, you can access it by the IP address of Raspberry Pi like:192.168.6.93

8. You can check the time by the following command on a Linux device.

sudo apt install ntpdate
sudo ntpdate 192.168.6.93

Working with STM32

Hardware connection

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

HAL examples

Download the demo codes.
Unzip and go into the directory of the STM32 example.
Open the STM32 project with Keil software.
Compile and download the code to the XNUCLEO-F103RB board.
Connect the UART2 of the XNUCLEO-F103RB board to PC and check the debug information by Serial Port Utility.

Working with Jetson Nano

Install Python library:

sudo apt-get update
sudo apt-get install python-serial
sudo apt-get install gpsd gpsd-clients 
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

Resource

Document

Demo codes

Demo codes

Software

u-center

FAQ

Question:How does U-center export data?

Answer:

You need to enable the Message before exporting data. The following figure is about the output of the RXM-RAWX of NEO-M8T.

Then, please click File->New, enter the name to be saved, choose to save the location, and click Yes; or you can click Yes directly. By now, the u-center started to record the data. After waiting for a while, you can click File-Save to save the GNSS information collected at the interval just now.

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Question: Why don't Beidou and Galileo work?