Exercise 9: GPS receiver

Introduction

Most GPS receivers use a simple serial interface for communication and provide their data in form of NMEA sentences to the host. See GPS receiver for more details. The goal of this exercise will therefore be to receive these messages over a UART port and to interpret them.

The GPS receiver may need quite some time to find satellites and to be ready to send valid messages. It will start blinking the red LED when this is the case.

Exercise 1: Receiving messages

Write a script that receives NMEA messages on ESP32 UART2, where Tx is re-mapped to D2 or GPIO21. Read the messages and print them as they come in.

Exercise 2: Interpreting the NMEA messages using micropyGPS

Download https://github.com/inmcm/micropyGPS and install micropyGPS.py in /lib on the ESP32 file system. Have a look at test_micropyGPS.py to understand how to use the parser. Run it on the PC.

Exercise 3: Interpreting real messages

First save a series of NMEA sentences on a file. Transfer the file to the PC and have them interpreted by the micropyGPS parser in the same fashion as the test_micropyGPS.py does. You should get a result similar to this log.

https://iotworkshop.africa/pub/IoT_Course_English/GPSAndInterfaceThroughUART/parserLog.txt

After that you may try to interpret the messages directly on the ESP32as they come in. The microGPS parser is already included in your MicroPython firmware.

Exercise 4: as_GPS

Peter Hinch has written an asynchronous GPS driver with a parser based on micropyGPS. The driver is already installed in your MicroPython binary. Use this driver to extract the information of exercise 3.

The documentation of as_GPS cant be found at https://github.com/peterhinch/micropython-async/blob/master/v3/docs/GPS.md

The exercise sheet in odt format:

https://iotworkshop.africa/pub/IoT_Course_English/GPSAndInterfaceThroughUART/exercise_6.odt

-- Uli Raich - 2020-08-04

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