Data logger for Raspberry

The objective of this project is to record raw NMEA frames from a GPS receive card.
I made the choice of a minimalist interface with a red led and a push button.
This program deals with parallel programming in Python.

Overview

1 Hardware

1.1 Equipments

What you will need:

Schematic ref	Description	Value
J1	raspberry pi
J2	neo6m module
SW1	push button
D1	led 5mm
C1	capacitor	100 nF
R1	resistor	10 kohm
R2	resistor	1 kohm
R3	resistor	330 ohm

Knolling

1.2 Wiring the GPS to the RPI

You have to be careful about RX and TX connections:

• connect the TX pin of the GPS to the RX pin of the RPI.
• connect the RX pin of the GPS to the TX pin of the RPI.

Wiring

1.3 Overview of the electronic schema

Resistance value for LED mounting:
It is commonly accepted that the standard LEDs work well with a resistance 100 times higher than the supplied voltage.
So I use in my assembly a resistance of 330ohm, for a voltage of 3.3 V

Mounting the push button:
The pull-up resistors allows to have a clear high or low voltage so that the RPI can read the input value unambiguously.

The capacitor:
When pressing the button there is a creation of interference signals induced, so we add a capacitor to improve the quality of the push button signal.
When the button is pressed, the capacitor discharges in a controlled manner and thus the signal is filtered.

Protection resistors:
The GPIO 4 pin can be initialized in the program as an output or as an input.
The purpose of the protection resistor is to protect the GPIO pin if it is accidentally set as an output rather than as an input.

Schema

2 Software

2.1 The detail of the design

• when the program starts, the LED flashes quickly, the program waits for the push button to be pressed.
• a short press on the push button:
  • triggers the recording of NMEA frames, the diode remains lit
  • or pauses recording, the LED flashes slowly
• a long press on the push button stops the program
• to restart the program, you must restart the Raspberry pi

_Flowchart_

2.2 Dependencies

• python 2.7
• python-serial

2.3 Installation

To launch the application on startup:

• copy the file app.py to the directory /home/pi/
• create a file raspberry-pi-gps-logger.service to the directory /lib/systemd/system/
• run the following command lines: systemctl start raspberry-pi-gps-logger and systemctl enable raspberry-pi-gps-logger

File raspberry-pi-gps-logger.service:

[Unit]
Description=Data recorder
After=multi-user.target

[Service]
Type=idle
ExecStart=/usr/bin/python /home/pi/app.py

[Install]
WantedBy=multi-user.target

Data post-processing

To view the recorded data, you need to convert the .nmea to .gpx
You can use the following command:
gpsbabel -i nmea -f file-in.nmea -o gpx -F file-out.gpx

Acknowledgements

Based on martinohanlon/pelmetcam/pelmetcam.py.

License

MIT License. See the LICENSE file for details.