GPS Speedometer

Using our Arduino-compatible GPS module and TFT Screen, this project displays basic GPS information such as longitude, latitude, altitude, speed, and distance travelled from point A to B. Information are stored on an SD card which can be exported and viewed via Google Maps. Powered from a micro-USB for easy powering off your phone charger while you’re in the car.

• Due to the limited size of the Arduino, we've separated the code into two code blocks:
  • gps_speedo for the gps speedometer
  • gps_recorder record the gps trip
• While it is possible to fit the two into one sketch, it's a tight fit and not very suitable for beginners. You are welcome to try though and see what you can conjure up. We've found this way is simpler and easy for you to dig through without having to worry about removing bootloaders or otherwise.

Bill of Materials

Qty	Product	Description
1	XC4430	Duinotech Leonardo
1	XC3712	GPS Receiver module
1	XC4630	2.8" TFT LCD screen.
		Some double sided and single sided tape

Suggested Extras

• WW4345 Wire wrap (use any colour)
  • Very thin wire that's perfect for small builds.
• XC4983 8GB SD card.
  • Use for logging GPS data.

Required Software and Libraries

Version numbers are at the time of this guide and might or might not work with later version.

Library	Author	Version
NeoGps	SlashDevin	4.2.9
NeoHWSerial	SlashDevin	Latest Github https://github.com/SlashDevin/NeoHWSerial
MCUFRIEND_kbv	David Prentice	2.9.8
SdFat	Bill Greiman	1.0.7

Notes

• NeoGps and NeoHWSerial are needed to run the GPS module, the NeoHWSerial library is a custom library that isn't yet in the library manager, but is needed to enable interrupt processing on the Serial line.

• You must modify line 150 of NMEAGPS_cfg.h to read:

#define NMEAGPS_INTERRUPT_PROCESSING

• You must also modify 159-161 of GPSport.h to read:

  #include <NeoHWSerial.h>    // NeoSerial or NeoSerial1 Interrupt-style processing
  //#include <AltSoftSerial.h>    // <-- DEFAULT.  Two specific pins required
  //#include <NeoICSerial.h>    // AltSoftSerial with Interrupt-style processing (see docs)

• MCUFRIEND_kbv needs to be modified to work with our TFT module. Read more Here

• SdFat provides us with an interface to FAT32 filesystems as well as provides a SoftwareSPI bus. We use 'SoftSPI' due to the case that Leonardo does not have the SPI pins on 10~13 as traditional UNOs do. This library is perfect for our needs.

• To enable, change line 85 of documents/libraries/SdFat/src/SdFatConfig.h to read:

#define ENABLE_SOFTWARE_SPI_CLASS 1

Connection Table

GPS module	TFT Screen
TX	Pin0 (unlabeled, next to J2)
VCC	5V
GND	GND

That's all there is to it, one connection (aside from power)

Assembly

To make the unit neat and organised, we're attaching the GPS module underneath the TFT screen. seeming there's only one connection, this is non-trivial.

First we'll use some single-sided tape to cover the connection pads that are at the bottom of the TFT screen.

The tape is a bit transparent so we coloured it in for you

Next we'll remove the solder connections from the GPS module, if you're unsure, follow the Guide

Then attach the module board to the underside of the TFT screen, in a suitable location, and solder the wires to where they have to go. For this, I used wire-wrap, which is very small, and fairly easy to work with if you manage to strip them without cutting the super-thin cable.

Connections to the GPS module that has been double-sided taped to the TFT module

The only final thing is the antenna. There's two locations for this, depending on whether you want to mangle your Leonardo or not. I opted to do it, by removing the ISCP connector from the Leonardo, giving room for the antenna to sit underneath the bottom of the TFT screen and using a small bit of tape to keep it in place. you can also sit it out to the side if you want, but be sure not to bump it around too much as the antenna lead is very thin and not designed to take stress.

Picture of how we set it up by removing the ISCP. if you don't want to remove the ISCP, you can use the alternative position but it's recommended to support the antenna in some way so it doesn't move around

That's it! you're done.

Programming

Programming has been done for you, so simply download the code and upload from the Arduino. Make sure to select the correct board ( Yun or Leonardo) and the correct Port.

At the top of the code is TZ_OFFSET which is set to 39600 - this is 39600 seconds from UTC, or +11 hours AEDT for Sydney daylight saving time. Use this to change your Time zone so it shows the correct time, for instance:

• If you are in Brisbane: you can use +11 * 60 *60 = 39600 for AEST

• If you are in Washington (daylight saving): you can use -4 * 60 * 60 = -14400 for EDT

Use

The GPS_speedo program will boot up and automatically tell you your location and speed. GPS_recorder will log your trip info to SD card with standard KVML format as used by Google Maps.

Contribution

We welcome suggestions and improvements to the code, send in a pull request and we'll review it to merge into main branch.