Limit #'s behind decimal?

Using Arduino Project Guidance
1

I'm making a TFT with a MEGA to show a GPS compass and GPS speed and miles to a waypoint and cardinal heading..... I want to limit the Speed which shows 0.00 to 00 with no decimal value. It's used on an Ultralight aircraft and there's no purpose for even tenths of a MPH.

My code for that line:
PrintText(10, 220, "SPEED " + String(dSpeed / 1.609) + " Mph", RED, 3);

Uses TinyGPSPlus

Wish I could add a picture or even send the full code. Thanks!

***FIX! In my code, all I had to do was add a " , 0 " in this line of code to find MPH...
PrintText(35, 210, "" + String(dSpeed / 1.609, 0) + " ", WHITE, 3);

I was also confused because earlier in the day I had deleted the SpeedKPH = gps.speed.kmph(); Because I didn't think it used it in the program. I was wrong! So then I was seeing the 0 for speed instead of 0.00, but it never registered any speed when moving, till I put the Kmph code back in.

2

Why can't you post the full code or at least a full but smaller sketch that illustrates the problem ?

As it stands we have no idea what the parameters of the PrintText() function are nor do we know why you are using Strings

3

You can send full code by inserting it in a post; see How to get the best out of this forum.

PrintText is not a standard function in Arduino. The print functions for floats take a second argument which is the number of digits after the dot; try to set it to 0 and test. E.g.

float_pi = 3.14;
Serial.println(+pi, 0);

However with your PrintText, I suspect that you need to cast to an int. Something like

PrintText(10, 220, "SPEED " + String((int)(dSpeed / 1.609)) + " Mph", RED, 3);
4

All right, but it's huge!

/* Added curentWaypoint for function with GPS waypoints
 * Added if ((gps.location.isValid()) && (currentWaypoint == '0'))
 * Added "HOME". Added code to change Name of GPS Waypoint. WAYPOINT & HOME
 * MEGA must be connected or you will get "Serial1 was not declared in this scope" error
 * MEGA  ***This is the one for Capitol Airport ***
 * Removed Date and Time
 * RED TFT (ILI9341)
 * Pin19  to 4th pin on sensor
 * GPS Sensor GT-U7
 * Displays Compass and GPS headers, SEEMS TO WORK!
 * Changed KPH to MPH
 * Changed Altitude Meters to Feet
 * Added GPS Valid Gren/Red box ***ONLY valid if 
 * GPS SAT signal is lost, not if wire #19 is 
 * pulled out and Arduino is not receiving signals.***
 * Added Dist and Heading to Capitol Airport Waukesha WI (can be changed)
 * NEED TO FIX GPS TIME ******************************************************
*/

#include <TinyGPSPlus.h>
#include <SoftwareSerial.h>
static const int RXPin = 18, TXPin = 19;
static const uint32_t GPSBaud = 9600;
#include <Arduino.h>
#define USE_ADAFRUIT_SHIELD_PINOUT 1
#include <Adafruit_GFX.h> 
#include <Adafruit_Sensor.h> 
#include <MCUFRIEND_kbv.h>
MCUFRIEND_kbv tft;

TinyGPSPlus gps;          // May have GPS TIME calculations

#include <SPI.h>
#include "Adafruit_GFX.h"
#include "Adafruit_ILI9341.h"

// Assign names to common 16-bit color values:
#define   BLACK  0x0000
#define   BLUE   0x001F
#define   RED    0xF800
#define   GREEN  0x07E0
#define   CYAN   0x07FF
#define   YELLOW 0xFFE0
#define   ORANGE 0xFD20
#define   WHITE  0xFFFF

String    Time, Date;
float     NumberSats, Latitude, Longitude, Bearing;
float     AltitudeMETRES, AltitudeMILES, AltitudeKM, AltitudeFEET;
float     SpeedKPH, SpeedMPH, SpeedKNOTS, SpeedMPS;
//float     distanceToWAYPOINT;           /////////////////////////

const int centreX  = 230; // Location of the compass display on screen
const int centreY  = 120;
const int diameter = 70; // Size of the compass
int       dx = centreX, dy = centreY;
int       last_dx = centreX, last_dy = centreY - diameter * 0.85;
int currentWaypoint = 0;

// For stats that happen every 5 seconds
unsigned long last = 0UL;

void setup()

{
  Serial.begin(115200);
  Serial1.begin(9600); // connect gps sensor
  //ss.begin(GPSBaud);
  //Serial.print("What the HECK!");

  tft.begin();            // Start the TFT display
  tft.setRotation(5);     // Rotate screen by 90°
  tft.setTextSize(2);     // Set medium text size
  tft.setTextColor(YELLOW);
  tft.fillScreen(BLACK);
  currentWaypoint = '0'; // 0=CAPITOL, 1=HOME, 2=HOLY HILL, 3=CARL, 4=???
}

void loop() {
  
  Latitude       = gps.location.lat();
  Longitude      = gps.location.lng();
  Bearing        = gps.course.deg();
  SpeedMPH       = gps.speed.mph();
  NumberSats     = gps.satellites.value();
  AltitudeMETRES = gps.altitude.meters();     // KEEP THIS!
  AltitudeFEET   = gps.altitude.feet();
  

// ********* GPS GOOD? This works ONLY if SAT signal is lost NOT if Pin19 is pulled out *******
if (gps.satellites.value ()> 3 )
   tft.fillRect(0, 0, 30, 8 * 4, GREEN); 
else   
   tft.fillRect(0, 0, 30, 8 * 4, RED);     //left,top,right,down * 4?, Green

// *** Adding Dist & Course to WAYPOINT *******************************************
if ((gps.location.isValid()) && (currentWaypoint == '0'))
  {
    PrintText(20, 0, "  CAPITOL", CYAN, 2);
  //PrintText(40, 0, "distanceToWAYPOINT:" + String(),2, 2);        //////////////
  tft.fillRect(45, 40, 90, 19 * 4, BLACK); //LAT, LONG, ALT, SAT area
  
  static const double WAYPOINT_LAT = 43.089619, WAYPOINT_LON = -88.179440;
      double distanceToWAYPOINT =
      TinyGPSPlus::distanceBetween(gps.location.lat(), gps.location.lng(), WAYPOINT_LAT, WAYPOINT_LON);
      double courseToWAYPOINT = TinyGPSPlus::courseTo(gps.location.lat(), gps.location.lng(), WAYPOINT_LAT, WAYPOINT_LON);
      tft.setTextColor(CYAN);
      tft.setCursor(150, 0);                                // Sets it back to not print over "WAYPOINT"
      tft.println(TinyGPSPlus::cardinal(courseToWAYPOINT));   // Prints "cardinal heading (SE) to gps location" on TFT
      tft.setCursor(190, 0);
      tft.println(distanceToWAYPOINT/1000*.6213712, 1);       // Prints Distance to WAYPOINT calculated for miles
      tft.setCursor(250, 0);
      tft.print("Miles");
  }
 

// end Addding Distance & Heading to WAYPOINT

// *** Adding Dist & Course to Home *******************************************
if ((gps.location.isValid()) && (currentWaypoint == '1'))
  {

PrintText(20, 0, "  HOME", CYAN, 2);
  //PrintText(40, 0, "distanceToWAYPOINT:" + String(),2, 2);        //////////////
  tft.fillRect(45, 40, 90, 19 * 4, BLACK);   //LAT, LONG, ALT, SAT area
    
  static const double WAYPOINT_LAT = 43.200000, WAYPOINT_LON = -88.300000;
      double distanceToWAYPOINT =
        TinyGPSPlus::distanceBetween(gps.location.lat(), gps.location.lng(), WAYPOINT_LAT, WAYPOINT_LON);
      double courseToWAYPOINT =
        TinyGPSPlus::courseTo( gps.location.lat(), gps.location.lng(), WAYPOINT_LAT, WAYPOINT_LON);

      tft.setTextColor(CYAN);
      tft.setCursor(150, 0);                                // Sets it back to not print over "WAYPOINT"
      tft.println(TinyGPSPlus::cardinal(courseToWAYPOINT));   // Prints "cardinal heading (SE) to gps location" on TFT
      tft.setCursor(190, 0);
      tft.println(distanceToWAYPOINT/1000*.6213712, 1);       // Prints Distance to WAYPOINT calculated for miles
      tft.setCursor(250, 0);
      tft.print("Miles");
  }
 

// end Addding Distance & Heading to HOME

// *** Adding Dist & Course to Home *******************************************
if ((gps.location.isValid()) && (currentWaypoint == '3'))
  {

PrintText(20, 0, "  CARL", CYAN, 2);
  //PrintText(40, 0, "distanceToWAYPOINT:" + String(),2, 2);        //////////////
  tft.fillRect(45, 40, 90, 19 * 4, BLACK);   //LAT, LONG, ALT, SAT area
    
  static const double WAYPOINT_LAT = 43.369462, WAYPOINT_LON = -88.592716;
      double distanceToWAYPOINT =
        TinyGPSPlus::distanceBetween(gps.location.lat(), gps.location.lng(), WAYPOINT_LAT, WAYPOINT_LON);
      double courseToWAYPOINT =
        TinyGPSPlus::courseTo(gps.location.lat(), gps.location.lng(), WAYPOINT_LAT, WAYPOINT_LON);

      tft.setTextColor(CYAN);
      tft.setCursor(150, 0);                                // Sets it back to not print over "WAYPOINT"
      tft.println(TinyGPSPlus::cardinal(courseToWAYPOINT));   // Prints "cardinal heading (SE) to gps location" on TFT
      tft.setCursor(190, 0);
      tft.println(distanceToWAYPOINT/1000*.6213712, 1);       // Prints Distance to WAYPOINT calculated for miles
      tft.setCursor(250, 0);
      tft.print("Miles");
  }
 

// end Addding Distance & Heading to CARL


// *** Adding Dist & Course to Home *******************************************
if ((gps.location.isValid()) && (currentWaypoint == '2'))
  {

PrintText(20, 0, "  HOLY HILL", CYAN, 2);
  //PrintText(40, 0, "distanceToWAYPOINT:" + String(),2, 2);        //////////////
  tft.fillRect(45, 40, 90, 19 * 4, BLACK);   //LAT, LONG, ALT, SAT area
    
  static const double WAYPOINT_LAT = 43.140000, WAYPOINT_LON = -88.190000;
      double distanceToWAYPOINT =
      TinyGPSPlus::distanceBetween(gps.location.lat(), gps.location.lng(), WAYPOINT_LAT, WAYPOINT_LON);
      double courseToWAYPOINT =
      TinyGPSPlus::courseTo(gps.location.lat(), gps.location.lng(), WAYPOINT_LAT, WAYPOINT_LON);

      tft.setTextColor(CYAN);
      tft.setCursor(150, 0);                                // Sets it back to not print over "WAYPOINT"
      tft.println(TinyGPSPlus::cardinal(courseToWAYPOINT));   // Prints "cardinal heading (SE) to gps location" on TFT
      tft.setCursor(190, 0);
      tft.println(distanceToWAYPOINT/1000*.6213712, 1);       // Prints Distance to WAYPOINT calculated for miles
      tft.setCursor(235, 0);
      tft.print("Miles");
  }
 

// end Addding Distance & Heading to HOLY HILL
      
  while (Serial1.available() > 0)
      gps.encode(Serial1.read());
  if  (gps.location.isUpdated())

  {
  Serial.print(F("LOCATION   Fix Age="));
    //Serial.print("***************");
    Serial.print(gps.location.isUpdated());
    //Serial.print(gps.location.age());
    //Serial.print(F("ms Raw Lat="));
    //Serial.print(gps.location.rawLat().negative ? "-" : "+");
    //Serial.print(gps.location.rawLat().deg);
    //Serial.print("[+");
    //Serial.print(gps.location.rawLat().billionths);
    //Serial.print(F(" billionths],  Raw Long="));
    //Serial.print(gps.location.rawLng().negative ? "-" : "+");
    //Serial.print(gps.location.rawLng().deg);
    //Serial.print("[+");
    //Serial.print(gps.location.rawLng().billionths);
    //Serial.print(F(" billionths],  Lat="));
    //Serial.print(gps.location.lat(), 6);
    //Serial.print(F(" Long="));
    //Serial.println(gps.location.lng(), 6);
  }

  //Serial.println("Time\t\tDate\t\tLAT\tLON\tSATS\tAlt\tBearing\tSpeed(KPH)");
  //Serial.println("----------------------------------------------------------------------------------");
  //Serial.print(Time                   + "\t");
  //Serial.print(Date                   + "\t");
  //Serial.print(String(Latitude, 3)    + "\t");
  //Serial.print(String(Longitude, 3)   + "\t");
  //Serial.print(String(NumberSats)     + "\t");
  //Serial.print(String(AltitudeMETRES) + "\t"); // Select as required
  //Serial.print(String(Bearing)        + "\t");
  //Serial.print(String(SpeedKPH)       + "\t"); // Select as required
  //Serial.print(String(SpeedMPH)       + "\t"); // Select as required
  //Serial.print(String(distanceToWAYPOINT) +  "\t"); ///////////////////////////////
  //Serial.println("\n");
  
  DisplayGPSdata(NumberSats, Latitude, Longitude, AltitudeMETRES, SpeedKPH, Bearing); // Select units as required
  smartDelay(1000);
  if (millis() > 5000 && gps.charsProcessed() < 10)  Serial.println(F("No GPS data received: check wiring"));
}
//#####################################################################
void DisplayGPSdata(float dNumberSats, float dLatitude, float dLongitude, float dAltitude, float dSpeed, float dBearing) {
  
//  PrintText(20, 0, "  WAYPOINT", CYAN, 2);
//  //PrintText(40, 0, "distanceToWAYPOINT:" + String(),2, 2);        //////////////
//  tft.fillRect(45, 40, 90, 19 * 4, BLACK);
  PrintText(0, 45, "LAT:" + String(dLatitude), YELLOW, 2);
  PrintText(0, 63, "LON:" + String(dLongitude), YELLOW, 2);
  PrintText(0, 81, "ALT:" + String(dAltitude * 3.28084, 1) + " FT", WHITE, 2);
  PrintText(0, 99, "SAT:" + String(dNumberSats, 0), YELLOW, 2);
  tft.fillRect(100, 220, 120, 22, BLACK);    // Left side to side, up and down, Right amount long, down for an amount, color (Blacks out old speed)
  PrintText(10, 220, "SPEED  " + String(dSpeed / 1.609) + " Mph", RED, 3); //
  // tft.fillRect(220, 218, 120, 18, BLACK);   // This was on far right of screen for ???
  tft.setCursor(200, 220);
  Display_Compass(dBearing);
}
//#####################################################################
void Display_Compass(float dBearing) {
  int dxo, dyo, dxi, dyi;
  tft.setCursor(0, 0);
  tft.drawCircle(centreX, centreY, diameter, WHITE); // Draw compass circle
  for (float i = 0; i < 360; i = i + 22.5) {
    dxo = diameter * cos((i - 90) * 3.14 / 180);
    dyo = diameter * sin((i - 90) * 3.14 / 180);
    dxi = dxo * 0.9;
    dyi = dyo * 0.9;
    tft.drawLine(dxo + centreX, dyo + centreY, dxi + centreX, dyi + centreY, WHITE);
  }
  PrintText((centreX - 5), (centreY - diameter - 18), "N", GREEN, 2);
  PrintText((centreX - 5), (centreY + diameter + 5) , "S", GREEN, 2);
  PrintText((centreX + diameter + 5),  (centreY - 5), "E", GREEN, 2);
  PrintText((centreX - diameter - 15), (centreY - 5), "W", GREEN, 2);
  dx = (0.85 * diameter * cos((dBearing - 90) * 3.14 / 180)) + centreX; // calculate X position ( Change dBearing to bearing? to get to WAYPOINT Airport?)
  dy = (0.85 * diameter * sin((dBearing - 90) * 3.14 / 180)) + centreY; // calculate Y position
  draw_arrow(last_dx, last_dy, centreX, centreY, 5, 5, BLACK);   // Erase last arrow
  draw_arrow(dx, dy, centreX, centreY, 5, 5, YELLOW);           // Draw arrow in new position
  last_dx = dx;
  last_dy = dy;
}
//#####################################################################
void draw_arrow(int x2, int y2, int x1, int y1, int alength, int awidth, int colour) {
  float distance;
  int dx, dy, x2o, y2o, x3, y3, x4, y4, k;
  distance = sqrt(pow((x1 - x2), 2) + pow((y1 - y2), 2));
  dx = x2 + (x1 - x2) * alength / distance;
  dy = y2 + (y1 - y2) * alength / distance;
  k = awidth / alength;
  x2o = x2 - dx;
  y2o = dy - y2;
  x3 = y2o * k + dx;
  y3 = x2o * k + dy;
  x4 = dx - y2o * k;
  y4 = dy - x2o * k;
  tft.drawLine(x1, y1, x2, y2, colour);
  tft.drawLine(x1, y1, dx, dy, colour);
  tft.drawLine(x3, y3, x4, y4, colour);
  tft.drawLine(x3, y3, x2, y2, colour);
  tft.drawLine(x2, y2, x4, y4, colour);
}

/*
//###########BEARING TO GPS WAYPOINT ###############  bearing is from "Bearing  = gps.course.deg();" 
String Bearing_to_Ordinal(float bearing) {

  if (bearing >= 348.75 || bearing < 11.25)  return "N";
  if (bearing >=  11.25 && bearing < 33.75)  return "NNE";
  if (bearing >=  33.75 && bearing < 56.25)  return "NE";
  if (bearing >=  56.25 && bearing < 78.75)  return "ENE";
  if (bearing >=  78.75 && bearing < 101.25) return "E";
  if (bearing >= 101.25 && bearing < 123.75) return "ESE";
  if (bearing >= 123.75 && bearing < 146.25) return "SE";
  if (bearing >= 146.25 && bearing < 168.75) return "SSE";
  if (bearing >= 168.75 && bearing < 191.25) return "S";
  if (bearing >= 191.25 && bearing < 213.75) return "SSW";
  if (bearing >= 213.75 && bearing < 236.25) return "SW";
  if (bearing >= 236.25 && bearing < 258.75) return "WSW";
  if (bearing >= 258.75 && bearing < 281.25) return "W";
  if (bearing >= 281.25 && bearing < 303.75) return "WNW";
  if (bearing >= 303.75 && bearing < 326.25) return "NW";
  if (bearing >= 326.25 && bearing < 348.75) return "NNW";
  return "?";
}
*/
//#####################################################################
void PrintText(int x, int y, String text, int colour, byte text_size) {
  tft.setCursor(x, y);
  tft.setTextColor(colour);
  tft.setTextSize(text_size);
  tft.print(text);
  tft.setTextColor(YELLOW); // Default colour
  tft.setTextSize(2);       // Default Text Size
}
//#####################################################################
static void smartDelay(unsigned long ms) {
  unsigned long start = millis();
  do {
    while (Serial1.available()) gps.encode(Serial1.read());
  } while (millis() - start < ms);
}
5

An alternative is to go the OOP route; you will have to write a few PrintText functions for the type of variables that you want to print. Some examples

/*
  print a text
*/
//#####################################################################
void PrintText(int x, int y, String var, int colour, byte text_size) {
  tft.setCursor(x, y);
  tft.setTextColor(colour);
  tft.setTextSize(text_size);
  tft.print(var);
  tft.setTextColor(YELLOW); // Default colour
  tft.setTextSize(2);       // Default Text Size
}

/*
  print a float with specified number of decimal digits
*/
//#####################################################################
void PrintText(int x, int y, float var, int digits, int colour, byte text_size) {
  tft.setCursor(x, y);
  tft.setTextColor(colour);
  tft.setTextSize(text_size);
  tft.print(var , digits);
  tft.setTextColor(YELLOW); // Default colour
  tft.setTextSize(2);       // Default Text Size
}

/*
  print a float without decimal digits
*/
//#####################################################################
void PrintText(int x, int y, float var, int colour, byte text_size) {
  tft.setCursor(x, y);
  tft.setTextColor(colour);
  tft.setTextSize(text_size);
  tft.print(var , 0);
  tft.setTextColor(YELLOW); // Default colour
  tft.setTextSize(2);       // Default Text Size
}

Not tested.

6

Thank you sir! I will try it out and test it, let you know what works. Thanks!

7

https://www.cplusplus.com/reference/cstdio/printf/

Look at the instructions for format specifiers.

8

So Happy to say, I added a comma and a 0 after the 1.609 and it works! ( Or did I just ask it to print a "0"? ) Will have to go jogging! Edited: Nope, I just told it to write "0". Will try more...
<PrintText(10, 220, "SPEED " + String(dSpeed / 1.609, 0) + " Mph", RED, 3);>

You are the best!

9

I'm sorry, I tried reading that and I'm sure I'm unable to comprehend 99% of it. Nothing stood out for formatting a number to skip anything past the decimal. I usually find parts of programs that I need, add them together to do what I need. Then spend hours fixing all the intricate parts that hate each other till it works. This program works, but I need to get rid of needless info, and eventually want to change it so the way points are not only shown as distance, but that the compass id now a cardinal heading to the way point. I thought That removing the ".00" from the speed would be easier than it is. Thanks!

10

These 3 examples are basically the same. The first one is to print as is, the second prints and you command the number of digits (which I would think you'd need a ".0" unless you are going less than 10 MPH, maybe not. And example 3 sets it to "0" digits after the decimal, but when I load it, and get in the car to go faster than walking, I never get anything other than a "0". Seems it should work, but it is disabling the dSpeed somehow.

11

Then use an integer data type rather than a float

12

Try String((int)(dSpeed / 1.609))

13

I'm not sure how to do that, but I'll play around a little...

Heli? I've got an MX Sport. There's also a Heli next to it, but it's been sitting for 25+ years! Trying to sell it for $3000 for our club.

14

"no matching function for call to 'String::String(const char*, unsigned int, int)'
Maybe I need to call the int before?

15 
PrintText(10, 220, "SPEED " + String(dSpeed / 1.609) + " Mph", RED, 3);

dSpeed is a float in the DisplayGPSdata() function. The value that you pass to it is held in the SpeedKPH variable which is also a float, but as you never change its value in the sketch it will always be zero so your original question is meaningless anyway

16 
 float dSpeed=PI*100;
   Serial.begin(115200);
   Serial.print(String((int)(dSpeed / 1.609)));

gives me

195

Did you leave the extra ,0 in there like:


String((int)(dSpeed / 1.609)),0);
17

Oops, So I deleted the SpeedKPH cause I didn't want it in KPH and it has miles. Let me put it back there and see what happens. I was starting to believe I had done something cause even when put back to how I had it, I didn't think it was working.

18

I did, but as UKHeliBob says, I think I need the SpeedKPH put back in. Seemed to work with the ", 0)" at the end of that section, at least work for the decimal, but I believe I've screwed it up by removing the SpeedKPH. More trial and lots of error!

19

It seems UKHeliBob was right, I've put the SpeedKMph back in and I'm running around the house (cause its raining) and I can get up to 4 MPH. Will test later in a car.

Thanks!

20

It seems you were right, I've put the SpeedKMph back in and I'm running around the house (cause its raining) and I can get up to 4 MPH. Will test later in a car. I didn't think I needed KMPH because I had MPH! Oh well!

So the easy answer was just adding the " , 0 " after the math!

PrintText(35, 210, "SPEED" + String(dSpeed / 1.609, 0) + " MPH ", WHITE, 3);

Thanks!