• Get the GPS data from the neo 6M connected through a USB to serial adapter to the PC and send the information to gpsd
• Run gpspipe or gpsmon to verify that the data are seen.
• Send the data to OpenStreetView and display them in marble. This is done with the map.qml file described in the second part of the tutorial

Getting NMEA information for gpsd from the ESP32

gpsd does not only allow reading GPS information from the serial line but it can also get this information from a TCP of UDP socket. It should therefore be possible to keep the ublox neo M6 connected to the ESP32 and write a simple TCP server (named ser2tcpServer.py. I use port 29998 for this server) which listens to a connection request from gpsd and then reads NMEA sentences from the ESP32 UART and transfers them to gpsd over the TCP socket. To get things to work we must:

• start the ser2tcpServer.py (on the ESP32)
• start gpsd with tcp://IP_OF_ESP32:29998

gpspipe -r | nc -l 29999

from where they are picked up by map.qml. The result will be the same map as shown above but the GPS source has been shifted from the PC serial port to the ESP32.

Reading NMEA sentences with the ESP32

Once the connection is made and the UART instantiated all you need is an endless loop to read the UART line by line. This is what you will see if you print the result:

These are sentences of the NMEA protocol. You will need a parser that extracts the relevant information from these messages. It is not too difficult to write such a parser yourself but why do you want to do it if the job has already be done for you? In fact Peter Hinch has a github repository with gps drivers containing all you need:

https://github.com/peterhinch/micropython-async/tree/master/gps

He uses the NMEA parser from https://github.com/inmcm/micropyGPS but adapted it to his asynchronous driver.

Then we can run gpsd as a foreground process (-N), specify the baud rate (-s 115200) and the serial port to which the neo 6M is connected (/dev/ttyUSB0):

gpsd -N -s 115200 /dev/ttyUSB0

Once the daemon is running we use gpspipe to see the NMEA sentences on the console: gpspipe -r

This time the the NMEA sentences are not picked up from the USB to serial converted but from the TCP/IP port 2947 where gpsd provides information to its clients.

Now that we know that gpsd is working normally we can start gspmon which extracts basic GPS information like latitude, longitude, altitude and time and some information about the satellites seen.

Finally we run xgps to give us a graphical representation of the satellites in the sky.

More programs are part of gpsd but I will let you discover those yourself.

Showing GPS position information on a map

There is a nice tutorial from the Linux journal describing how to use gpsd when taking GPS information from a mobile phone:

• https://www.linux-magazine.com/Issues/2018/210/Tutorial-gpsd#article_f2
• https://www.linux-magazine.com/Issues/2018/210/Tutorial-gpsd/(offset)/3#article_i3

The strategy will be this:

• Get the GPS data from the neo 6M connected through a USB to serial adapter connected to the PC and send the information to gpsd
• Run gpsmon to verify that the data are seen.
• Send the data to OpenStreetView and display them in marble.
• Move the neo 6M to the ESP32 and write a program that transfers the NMEA sentences to gpsd running on the PC through a tcp socket.

Connecting the GPS receiver to your PC

In order to read out the GPS receiver from the PC we need a USB to serial converter:

As can be seen on the photo the connections must be made as follows (pin 1 is the leftmost pin)

ublox u-center

ublox provides a Windows application for its GPS receivers named u-center which you can download from https://www.u-blox.com/en/product/u-center. Its user guide can be found at https://www.u-blox.com/sites/default/files/u-center_Userguide_%28UBX-13005250%29.pdf. It is possible to run this application on Linux using the Windows emulator wine. u-center allows you to connect to a Windows com port in order to communicate with the receiver. When running the u-center installation you will get the executable in
~/.wine/drive_c/Program Files (x86)/u-blox/u-center_v20.06.01

Finally we must figure out to which Windows com port our USB to serial adapter corresponds to. Looking at ~/.wine/dosdevices shows that /dev/ttyUSB0 is mapped to com33.

ublox GPS receivers use 2 different protocols

• the NMEA protocol
• a proprietary binary protocol, which not only transmits GPS data but also allows to configure the receiver

u-center allows you to change the baud rate (I selected 115200 baud, which I also use to communicate with the ESP32) and to save this change in battery backed up RAM such that it can be recovered when the receiver is restarted after a power down.

Here is a screen dump of the running u-center application:

gpsd

The GPS daemon gpsd connects to a GPS receiver and provides its data to clients over a TCP connection.You can find it on https://gpsd.gitlab.io/gpsd/index.html

Reading NMEA sentences with the ESP32

https://docs.micropython.org/en/latest/library/machine.UART.html#machine-uart

uart2=machine.UART(2, baudrate=9600, rx=21, tx=22, timeout=10000)

These are sentences of the NMEA protocol. You will need a parser that extracts the relevant information from these messages. It is not too difficult to write such a parser yourself but why do you want to do it if the job has already be done for you? In fact Peter Hinch has a github repository with gps drivers containing all you need:

https://github.com/peterhinch/micropython-async/tree/master/gps

He uses the NMEA parser from https://github.com/inmcm/micropyGPS but adapted it to his asynchronous driver.

The Neo 6M GPS receiver

The card on which the Neo 6M GPS receiver is mounted has 4 connection pins (starting from the left):

As you can see from the pin names, the GPS receiver is controlled/read out through a UART. Default baud rate is 9600 baud. The pins on the ESP32 correspond to UART2 of the ESP32 chip.

Here is a photo of the device:

-- Uli Raich - 2020-07-01

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