Published August 18, 2018 © GPL3+

Portable GPS Tracker with MAX32620FTHR

Build a GPS logger / tracker as a hiking tool, and check GPS when a smartphone is not available.

BeginnerFull instructions providedOver 1 day1,694

Things used in this project

Hardware components

GPS Module (Generic)

Adafruit 1.8 inch TFT display

Maxim Integrated MAX32620FTHR

Software apps and online services

mbed

Story

A GPS tracker logger is a device that records GPS data. It can be used for tracking assets, monitoring position of pets, people, cars... you name it.

It can also be used for fun outdoor activity such as hiking or geo-caching. Normally a GPS tracker is fairly small and low power. The MAX32620 dev-board from Maxim is a nifty low power ARM MPU board which is tailor made for wearable devices. I thought it would be a good project to build a small GPS logger with a TFT display.

Hardware

The hardware is composed of the MAX32620FTHR development board, a UBlox-6 GPS module, an 1.8 inch TFT screen as well as the MAX77650 programmable LIPO charger/regulator and the MAX17055 LIPO fuel gauge.

The Ublox-6 GPS module is connected via the serial interface to the MAX32620FTHR. The ST7735 display is connected via the SPI0 bus. An SD card was also used for data logging. The SD card makes use of the same SPI bus but uses a different chip select.

The MAX77650 LIPO charger provides the power for the MCU and charging for the LIPO battery. The MAX17055 Fuel gauge purpose is to query the battery and provide a status of the State of Charge including voltage, current and battery temperature.

The connection to the board pinout diagram are as follows:

GPS is connected to UART2 pins, TX and RX.

TFT is connected to follwoing PMOD connector pins:

LITE -> VDD,

MISO to P1_0

MOSI to P1_1

TFT_CS to P1_3

SCK to P1_0

Firmware

I used mbed framework to implement the firmware. Basically the MAX32620FTHR queries the GPS every second and updates the TFT display with the data in real time. Since this is a low power solution intended to last for a long time the MCU shuts down the TFT display after 15 seconds.

Initially I tried to use a pass-through bridge to stream data to the PC. I found that the Mbed framework has an issue when two UART are executed so the debug serial would not work simultaneously with the GPS serial.I then piped the GPS data to the TFT display and it worked.

Next a timer was used to provide timestamp functionality for the data-logging option. When the GPS tracker is powered on a new file is opened on the SD card and the GPS data is continuously written. The SD filesystem library was used to add data-loggin capability to the GPS tracker.

The solution makes also use of the MAX fuel gauge which gives the LIPO battery voltage, temperature and current consumption. The hardware also uses the SIMO buck regulator.To display images on the TFT display I downloaded the image as a JPEG file.

Battery image

Then I used FSResizer http://www.faststone.org/FSResizerDetail.htm

to resize the image to 50x50 pixels. The next step was converting the image to an array to display it on the TFT display.

For this task I used lcd-image-converter-20161012. Since each pixel is 16 bit select the RGB 565 scheme.

The image is then exported from file convert. Now the image is included as a header file on the main application file.

The main application initializes the TFT display, configures the LIPO charger to output 3.3V and disables the LDO, next the fuel gauge is configured using a sense resistor to 50mohm.

The main program loop constantly queries the satellites in view when the GPS acquires a lock and updates the TFT display every 4 seconds.

The TFT display alternates between showing the battery status with battery current and voltage.

Notice that when the programmer and the USB is unplugged the board consumes energy so the current is negative. When the board is plugged in the current consumption is positive which means the board is being charged.T

Project Code

The project code is uploaded under this page:

https://os.mbed.com/users/DimiterK/code/MAX32620FTHR_GPS_Tracker/

So this shows how to quickly prototype a low power GPS tracker/logger with the MAX32620FTHR board. Obviously you can add a bunch of features to this app. Make it so, number 13.

Code

GPS tracker

// dhq August 2018
// Hackster Contest
#include "mbed.h"
#include <math.h>
#include <stdlib.h>

#include "SerialGPS.h"
#include "LCD_Driver.h"
#include "LCD_GUI.h"
#include "MAX32620FTHR.h"
#include "MAX77650.h"
#include "MAX17055.h"

#include "GPSimg.h"
#include "BatteryImg.h"

 
#define POWER_HOLD_OFF 0 
#define POWER_HOLD_ON 1 

// Configure GPIO voltage
MAX32620FTHR max32620fthr(MAX32620FTHR::VIO_3V3);

#define BACKGROUND  BLACK
#define FOREGROUND  YELLOW
#define DELAY 1000

I2C i2c(I2C2_SDA, I2C2_SCL);
DigitalOut  myled(LED1);
SerialGPS   gps(P3_1, P3_0,9600);

MAX17055 max17055(i2c);             // Fuel gauge
MAX77650 max77650(i2c);             // MAX77650 PMIC and Charger

// Configure PMIC to drive green LED
static const char ledGreen[] = {
    MAX77650::CNFG_LED0_A,
    0x04, 0x44, 0x04,
    0x0F, 0x0F, 0x0F,
    0x01,
};

DigitalOut pw_Hold(P2_2, POWER_HOLD_ON); 
//SDFileSystem sd(P0_5, P0_6, P0_4, P1_3, "sd"); // the pinout on the mbed 


int main() {
    
    // Configure TFT display
    LCD_SCAN_DIR LCD_ScanDir = SCAN_DIR_DFT;//SCAN_DIR_DFT = D2U_L2R
    LCD_Init(LCD_ScanDir ); 
    
    wait_ms(1000);
    
    LCD_Clear(BLACK);
    GUI_DrawRectangle(0,0,156,127,RED,DRAW_EMPTY,DOT_PIXEL_2X2);
    myled = !myled; // toggle a led

    char sats[16] = {};
    char longitude[16] = {};
    char latitude[16] = {};
    char geoid[16] = {};
    char altitude[16] = {};
    char time[16] = {};  
    
    char voltage[16] = {};   
    char avgVoltage[16] = {};  
    char current[16] = {};  
                    
    ///int status;
    float f_value;
    
    // Configure fuel gauge
    // Set sense resistor value
    max17055.init(0.05f);

    // Turn off Low-Dropout Linear Regulator (LDO); unused on MAX32620FTHR platform
    max77650.disableLDO();
    
    // Set SIMO Buck-Boost Regulator 2 target voltage; provides VDDIOH
    max77650.setSBB2Voltage(3.3f);

    // Turn PMIC green LED on, red and blue off
    max77650.writeReg(ledGreen, sizeof(ledGreen));
    

    while(1) {

        wait(0.5f); // wait a small period of time
        
        if (gps.sample()) {
            myled = myled ? 0 : 1;
 
            
            sprintf(sats, "SAT: %d ", gps.sats);
            sprintf(longitude, "LONG: %2.2f ", gps.longitude);
            sprintf(latitude, "LAT: %2.2f ", gps.latitude);
            sprintf(altitude, "ALT: %2.2f ", gps.alt);
            sprintf(geoid, "GEOID: %2.2f ", gps.geoid);
            sprintf(time, "TIME: %2.2f ", gps.time);

            LCD_Clear(BLACK);
            GUI_DisplayImage(50,10,gps_lock,50,50);
            GUI_DrawRectangle(0,0,156,127,YELLOW,DRAW_EMPTY,DOT_PIXEL_2X2);

            GUI_DisString_EN(10,80,sats,&Font12,GUI_BACKGROUND,YELLOW);
            GUI_DisString_EN(10,90,longitude,&Font12,GUI_BACKGROUND,YELLOW);
            GUI_DisString_EN(10,100,latitude,&Font12,GUI_BACKGROUND,YELLOW);
            GUI_DisString_EN(10,110,altitude,&Font12,GUI_BACKGROUND,CYAN);
 
            wait(2);
            LCD_Clear(BLACK);
            
            // Print formatted voltage, and battery current 
            max17055.v_cell(&f_value);
            sprintf(voltage,"V=%6.2fV", f_value); 
            max17055.current(&f_value);
            sprintf(current,"I=%6.2fmA", f_value);

            GUI_DisplayImage(50,10,batt_full,50,50);    
            GUI_DisString_EN(10,70,voltage,&Font20,GUI_BACKGROUND,YELLOW);
            GUI_DisString_EN(10,100,current,&Font20,GUI_BACKGROUND,CYAN);
            
            wait(2);


        }    
        myled = !myled; // toggle a led
    }
}

Credits

Dimiter Kendri

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Robotics and AI

Portable GPS Tracker with MAX32620FTHR

Things used in this project

Hardware components

Software apps and online services

Story

Hardware

Firmware

Project Code

Schematics

dev-board-schematics.png

Code

GPS tracker

GPS tracker

Credits

Dimiter Kendri

Comments

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Portable GPS Tracker with MAX32620FTHR

Portable GPS Tracker with MAX32620FTHR

Things used in this project

Hardware components

Software apps and online services

Story

Hardware

Firmware

Project Code

Schematics

dev-board-schematics.png

Code

GPS tracker

GPS tracker

Credits

Dimiter Kendri

Comments

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