Published June 6, 2016 © Apache-2.0

GPS Based Boat/ATV Speedometer

This could be the easiest one yet.

BeginnerFull instructions provided2 hours1,165

Things used in this project

Hardware components

Relay (generic)

Ananlog Meter

Resistor 221 ohm

Value depends on Meter sensitivity....

Software apps and online services

Arduino IDE

Hand tools and fabrication machines

Soldering iron (generic)

Story

When looking at the GPS sentence structure is said "Speed over ground, Knots" and I immediately thought Boat....

This could easily be adapted to any other use even that ATV or power wheels jeep!

Step 1: Schematic and Code

All you really need is a 1K resistor on the PWM out pin connected to an analog meter movement. Or better yet a 5K pot. I don't like pots because they drift from vibration but it would make it easier to calibrate the meter.

I usually like to adjust the resistor so a value of 240 gives full scale deflection. This way you can "pin" the needle....

I added a relay for an over speed alarm and a serial port to echo the raw GPS data to other devices. Might as well use it......

Step 2: The Shield

1 / 5

The shield is pretty straight forward. Almost verbatim from the data sheet for the Max232 chip.

I used a KSP-13 Darlington since I have dozens left over from other projects. You could probably get away with a 2N2222 but the Linkit One has a 1mA output limit so I like the extra gain.

Step 3: The Meter

1 / 4

This can be a hard choice. I prefer older or obscure analog meters.

I chose this great edge view meter I got at a surplus house.

Its only 200uA for full scale so no amplifier needed from the Linkit One's PWM output.

Step 4: Power Supply

1 / 3

I used a commercial USB car charger adapter module. This is overkill but you can tap off it for other devices.

If you get one of these shorty USB cables you can connect the Linkit One without any soldering. Just make sure you get the right one or you'll have leftovers too.

Step 5: Housing

1 / 11

For an enclosure I used an old Wall Wart box. This also came form a surplus house. It was never used but got pretty discolored after years in the drawer.

All the power components fit in the bottom. A spacer keeps the Linkit from touching anything. Its a tight fit so no mounting bolts just a little foam rubber will do it.

First time around I tried using a coax power jack. BIG MISTAKE. They fall out easily on bumps as found out in my car. Its worse on choppy waters. Use aviation connectors and you'll be much happier. The 4 pin is for power in and meter out. The 7 pin handles serial data and alarm contacts.

Step 6: Alarm

1 / 3

Audible alarms probably wouldn't do me much good. You can use red 12V pilot lights like these. I went for the BIG Jeweled indicators to match my meter's age.

Step 7: Waiting for a Trial Run

1 / 2

It's done and waiting for it's maiden voyage. I may make a smaller version for my golf cart.

Code

GPS_Boat_Speedometer.ino

//****************************************************************
//*  Name    : GPS Boat Speedo                                   *
//*  Author  : Robert Joseph Korn                                *
//*  Date    : 12/18/15                                          *
//*  Version : 1.1                                               *
//*  Notes   :                                                   *
//*          :                                                   *
//****************************************************************
#include <SPI.h>
#include <LGPS.h>

gpsSentenceInfoStruct info;

double spd;
String dataString;
int tmp ;
int num ;
int meter = 9;
int alarm = 6;
int limit = 35;

static unsigned char getComma(unsigned char num,const char *str)
{
  unsigned char i,j = 0;
  int len=strlen(str);
  for(i = 0;i < len;i ++)
  {
     if(str[i] == ',')
      j++;
     if(j == num)
      return i + 1; 
  }
  return 0; 
}

static double getDoubleNumber(const char *s)
{
  char buf[10];
  unsigned char i;
  double rev;
  
  i=getComma(1, s);
  i = i - 1;
  strncpy(buf, s, i);
  buf[i] = 0;
  rev=atof(buf);
  return rev; 
}

static double getIntNumber(const char *s)
{
  char buf[10];
  unsigned char i;
  double rev;
  
  i=getComma(1, s);
  i = i - 1;
  strncpy(buf, s, i);
  buf[i] = 0;
  rev=atoi(buf);
  return rev; 
}

void parseGPRMC(const char* GPRMCstr)
{
  if(GPRMCstr[0] == '$')
  {
    tmp = getComma(7, GPRMCstr);
    spd = getDoubleNumber(&GPRMCstr[tmp]);
    tmp = spd * 100 ;
    tmp = map(tmp,0,5000,0,232);
    analogWrite(meter, tmp);
    if(spd > limit)
     {
        digitalWrite(alarm, HIGH);  
     } else { 
        digitalWrite(alarm, LOW);   
     }
  }
}


void setup() {
  pinMode(alarm, OUTPUT);     
  digitalWrite(alarm, LOW);   
  Serial1.begin(4800);
  LGPS.powerOn();
}

void loop() {
  LGPS.getData(&info);
  Serial1.print((char*)info.GPRMC); 
  Serial1.print((char*)&info); 
  parseGPRMC((const char*)info.GPRMC);
  delay(1000);  
}

Credits

Robert Korn

15 projects • 27 followers

I Made the Internet of Things before people had a name for it.

GPS Based Boat/ATV Speedometer

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Step 1: Schematic and Code

Step 2: The Shield

Step 3: The Meter

Step 4: Power Supply

Step 5: Housing

Step 6: Alarm

Step 7: Waiting for a Trial Run

Schematics

Schematic

Code

GPS_Boat_Speedometer.ino

Credits

Robert Korn

Comments

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GPS Based Boat/ATV Speedometer

GPS Based Boat/ATV Speedometer

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Step 1: Schematic and Code

Step 2: The Shield

Step 3: The Meter

Step 4: Power Supply

Step 5: Housing

Step 6: Alarm

Step 7: Waiting for a Trial Run

Schematics

Schematic

Code

GPS_Boat_Speedometer.ino

Credits

Robert Korn

Comments

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