CircuitPython & Python

You can easily use a GPS module with Python or CircuitPython code in addition to Arduino.  Python code is well suited for parsing and processing the text output from GPS modules and this Adafruit CircuitPython GPS module handles most of the work for you!

CircuitPython MicroController Wiring

First make sure to wire up the GPS module to your CircuitPython board so that the hardware UART pins are used.  Here's an example with the Metro M0 Express:

  • Board 5V or 3.3V to GPS module VIN.
  • Board GND to GPS module GND.
  • Board serial TX to GPS module RX.
  • Board serial RX to GPS module TX.

Python Computer Wiring

Since there's dozens of Linux computers/boards you can use we will show wiring for Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux to see whether your platform is supported.

Here you have two options: An external USB-to-serial converter, or the built-in UART on the Pi's TX/RX pins. Here's an example of wiring up the USB-to-serial converter:

  • GPS Vin  to USB 5V or 3V (red wire on USB console cable)
  • GPS Ground to USB Ground (black wire)
  • GPS RX to USB TX (green wire)
  • GPS TX to USB RX (white wire)

Here's an example using the Pi's built-in UART:

  • GPS Vin  to 3.3V (red wire)
  • GPS Ground to Ground (black wire)
  • GPS RX to TX (green wire)
  • GPS TX to RX (white wire)

If you want to use the built-in UART, you'll need to disable the serial console and enable the serial port hardware in raspi-config. See the UART/Serial section of the CircuitPython on Raspberry Pi guide for detailed instructions on how to do this.

CircuitPython Installation of GPS Library

Next you'll need to install the Adafruit CircuitPython GPS library on your CircuitPython board.  Remember this module is for Adafruit CircuitPython firmware and not MicroPython.org firmware!

First make sure you are running the latest version of Adafruit CircuitPython for your board.

Next you'll need to install the necessary libraries to use the hardware--carefully follow the steps to find and install these libraries from Adafruit's CircuitPython library bundle.  For example the Circuit Playground Express guide has a great page on how to install the library bundle for both express and non-express boards.

Remember for non-express boards like the Trinket M0, Gemma M0, and Feather/Metro M0 basic you'll need to manually install the necessary libraries from the bundle:

  • adafruit_gps.mpy

You can also download the adafruit_gps.mpy file from the Adafruit CircuitPython GPS releases page.

Before continuing make sure your board's lib folder or root filesystem has the adafruit_gps.mpy, files and folders copied over.

Python Installation of GPS Library

You'll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This may require verifying you are running Python 3. Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready!

Once that's done, from your command line run the following command:

sudo pip3 install adafruit-circuitpython-gps

Usage

To demonstrate the usage of the GPS module in CircuitPython let's look at a complete program example, the simple.py file from the module's examples.

CircuitPython Microcontroller

With a CircuitPython microcontroller, save this file as main.py on your board, then open the REPL connection to the board to see its output

Linux/Computer/Raspberry Pi with Python

If you're running gps_simpletest.py on the Raspberry Pi (or any computer), you'll have to make some changes.

On the Raspberry Pi, comment out the uart = busio(...) line, and uncomment the import serial and uart = serial.Serial(...) lines, changing /dev/ttyUSB0 to the appropriate serial port.  Now you can run the program with the following command:

python3 gps_simpletest.py

Example Parsing Code

# Simple GPS module demonstration.
# Will wait for a fix and print a message every second with the current location
# and other details.
import time
import board
import busio

import adafruit_gps


# Define RX and TX pins for the board's serial port connected to the GPS.
# These are the defaults you should use for the GPS FeatherWing.
# For other boards set RX = GPS module TX, and TX = GPS module RX pins.
RX = board.RX
TX = board.TX

# Create a serial connection for the GPS connection using default speed and
# a slightly higher timeout (GPS modules typically update once a second).
uart = busio.UART(TX, RX, baudrate=9600, timeout=3000)

# for a computer, use the pyserial library for uart access
#import serial
#uart = serial.Serial("/dev/ttyUSB0", baudrate=9600, timeout=3000)

# Create a GPS module instance.
gps = adafruit_gps.GPS(uart, debug=False)

# Initialize the GPS module by changing what data it sends and at what rate.
# These are NMEA extensions for PMTK_314_SET_NMEA_OUTPUT and
# PMTK_220_SET_NMEA_UPDATERATE but you can send anything from here to adjust
# the GPS module behavior:
#   https://cdn-shop.adafruit.com/datasheets/PMTK_A11.pdf

# Turn on the basic GGA and RMC info (what you typically want)
gps.send_command(b'PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
# Turn on just minimum info (RMC only, location):
#gps.send_command(b'PMTK314,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
# Turn off everything:
#gps.send_command(b'PMTK314,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
# Tuen on everything (not all of it is parsed!)
#gps.send_command(b'PMTK314,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0')

# Set update rate to once a second (1hz) which is what you typically want.
gps.send_command(b'PMTK220,1000')
# Or decrease to once every two seconds by doubling the millisecond value.
# Be sure to also increase your UART timeout above!
#gps.send_command(b'PMTK220,2000')
# You can also speed up the rate, but don't go too fast or else you can lose
# data during parsing.  This would be twice a second (2hz, 500ms delay):
#gps.send_command(b'PMTK220,500')

# Main loop runs forever printing the location, etc. every second.
last_print = time.monotonic()
while True:
    # Make sure to call gps.update() every loop iteration and at least twice
    # as fast as data comes from the GPS unit (usually every second).
    # This returns a bool that's true if it parsed new data (you can ignore it
    # though if you don't care and instead look at the has_fix property).
    gps.update()
    # Every second print out current location details if there's a fix.
    current = time.monotonic()
    if current - last_print >= 1.0:
        last_print = current
        if not gps.has_fix:
            # Try again if we don't have a fix yet.
            print('Waiting for fix...')
            continue
        # We have a fix! (gps.has_fix is true)
        # Print out details about the fix like location, date, etc.
        print('=' * 40)  # Print a separator line.
        print('Fix timestamp: {}/{}/{} {:02}:{:02}:{:02}'.format(
            gps.timestamp_utc.tm_mon,   # Grab parts of the time from the
            gps.timestamp_utc.tm_mday,  # struct_time object that holds
            gps.timestamp_utc.tm_year,  # the fix time.  Note you might
            gps.timestamp_utc.tm_hour,  # not get all data like year, day,
            gps.timestamp_utc.tm_min,   # month!
            gps.timestamp_utc.tm_sec))
        print('Latitude: {0:.6f} degrees'.format(gps.latitude))
        print('Longitude: {0:.6f} degrees'.format(gps.longitude))
        print('Fix quality: {}'.format(gps.fix_quality))
        # Some attributes beyond latitude, longitude and timestamp are optional
        # and might not be present.  Check if they're None before trying to use!
        if gps.satellites is not None:
            print('# satellites: {}'.format(gps.satellites))
        if gps.altitude_m is not None:
            print('Altitude: {} meters'.format(gps.altitude_m))
        if gps.track_angle_deg is not None:
            print('Speed: {} knots'.format(gps.speed_knots))
        if gps.track_angle_deg is not None:
            print('Track angle: {} degrees'.format(gps.track_angle_deg))
        if gps.horizontal_dilution is not None:
            print('Horizontal dilution: {}'.format(gps.horizontal_dilution))
        if gps.height_geoid is not None:
            print('Height geo ID: {} meters'.format(gps.height_geoid))

When the code runs it will print a message every second, either an update that it's still waiting for a GPS fix:

Or once a fix has been established (make sure the GPS module has a good view of the sky!) it will print details about the current location and other GPS data:

Let's look at the code in a bit more detail to understand how it works.  First the example needs to import a few modules like the built-in busio and board modules that access serial ports and other hardware:

import board
import busio
import time

Next the GPS module is imported:

import adafruit_gps

Now a serial UART is created and connected to the serial port pins the GPS module will use, this is the low level transport layer to communicate with the GPS module:

# Define RX and TX pins for the board's serial port connected to the GPS.
# These are the defaults you should use for the GPS FeatherWing.
# For other boards set RX = GPS module TX, and TX = GPS module RX pins.
RX = board.RX
TX = board.TX
 
# Create a serial connection for the GPS connection using default speed and
# a slightly higher timeout (GPS modules typically update once a second).
uart = busio.UART(TX, RX, baudrate=9600, timeout=3000)

# for a computer, use the pyserial library for uart access
#import serial
#uart = serial.Serial("/dev/ttyUSB0", baudrate=9600, timeout=3000)

Once a UART object is available with a connected GPS module you can create an instance of the GPS parsing class.  You need to pass this class the UART instance and it will internally read new data from the GPS module connected to it:

gps = adafruit_gps.GPS(uart)

Before reading GPS data the example configures the module by sending some custom NMEA GPS commands that adjust the amount and rate of data.  Read the comments to see some options for adjust the rate and amount of data, but typically you want the defaults of core location info at a rate of once a second:

# Initialize the GPS module by changing what data it sends and at what rate.
# These are NMEA extensions for PMTK_314_SET_NMEA_OUTPUT and
# PMTK_220_SET_NMEA_UPDATERATE but you can send anything from here to adjust
# the GPS module behavior:
#   https://cdn-shop.adafruit.com/datasheets/PMTK_A11.pdf
 
# Turn on the basic GGA and RMC info (what you typically want)
gps.send_command('PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
# Turn on just minimum info (RMC only, location):
#gps.send_command('PMTK314,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
# Turn off everything:
#gps.send_command('PMTK314,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
# Tuen on everything (not all of it is parsed!)
#gps.send_command('PMTK314,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0')
 
# Set update rate to once a second (1hz) which is what you typically want.
gps.send_command('PMTK220,1000')
# Or decrease to once every two seconds by doubling the millisecond value.
# Be sure to also increase your UART timeout above!
#gps.send_command('PMTK220,2000')
# You can also speed up the rate, but don't go too fast or else you can lose
# data during parsing.  This would be twice a second (2hz, 500ms delay):
#gps.send_command('PMTK220,500')

If you want you can send other custom commands to the GPS module with the send_commandfunction shown above.  You don't need to worry about adding a NMEA checksum to your command either, the function will do this automatically (or not, set add_checksum=False as a parameter and it will skip the checksum addition). 

Now we can jump into a main loop that continually updates data from the GPS module and prints out status.  The most important part of this loop is calling the GPS update function:

    # Make sure to call gps.update() every loop iteration and at least twice
    # as fast as data comes from the GPS unit (usually every second).
    # This returns a bool that's true if it parsed new data (you can ignore it
    # though if you don't care and instead look at the has_fix property).
    gps.update()

Like the comments mention you must call updated every loop iteration and ideally multiple times a second.  Each time you call update it allows the GPS library code to read new data from the GPS module and update its state.  Since the GPS module is always sending data you have to be careful to constantly read data or else you might start to lose data as buffers are filled.

You can check the has_fix property to see if the module has a GPS location fix, and if so there are a host of attributes to read like latitude and longitude (available in degrees):

        if not gps.has_fix:
            # Try again if we don't have a fix yet.
            print('Waiting for fix...')
            continue
        # We have a fix! (gps.has_fix is true)
        # Print out details about the fix like location, date, etc.
        print('=' * 40)  # Print a separator line.
        print('Fix timestamp: {}/{}/{} {:02}:{:02}:{:02}'.format(
                gps.timestamp_utc.tm_mon,   # Grab parts of the time from the
                gps.timestamp_utc.tm_mday,  # struct_time object that holds
                gps.timestamp_utc.tm_year,  # the fix time.  Note you might
                gps.timestamp_utc.tm_hour,  # not get all data like year, day,
                gps.timestamp_utc.tm_min,   # month!
                gps.timestamp_utc.tm_sec))
        print('Latitude: {} degrees'.format(gps.latitude))
        print('Longitude: {} degrees'.format(gps.longitude))
        print('Fix quality: {}'.format(gps.fix_quality))
        # Some attributes beyond latitude, longitude and timestamp are optional
        # and might not be present.  Check if they're None before trying to use!
        if gps.satellites is not None:
            print('# satellites: {}'.format(gps.satellites))
        if gps.altitude_m is not None:
            print('Altitude: {} meters'.format(gps.altitude_m))
        if gps.track_angle_deg is not None:
            print('Speed: {} knots'.format(gps.speed_knots))
        if gps.track_angle_deg is not None:
            print('Track angle: {} degrees'.format(gps.track_angle_deg))
        if gps.horizontal_dilution is not None:
            print('Horizontal dilution: {}'.format(gps.horizontal_dilution))
        if gps.height_geoid is not None:

Notice some of the attributes like altitude_m are checked to be None before reading.  This is a smart check to put in your code too because those attributes are sometimes not sent by a GPS module.  If an attribute isn't sent by the module it will be given a None/null value and attempting to print or read it in Python will fail.  The core attributes of latitudelongitude, and timestamp are usually always available (if you're using the example as-is) but they might not be if you turn off those outputs with a custom NMEA command!

That's all there is to reading GPS location with CircuitPython code!

This guide was first published on Aug 23, 2012. It was last updated on Oct 21, 2018. This page (CircuitPython & Python) was last updated on Oct 01, 2018.