arduino gps speedo.

arduinogps.ino

#include <Adafruit_SSD1306.h>
#include <NMEAGPS.h>

Adafruit_SSD1306 display(128, 64, &Wire, 4);
static NMEAGPS  gps;

void setup() {
  Serial.begin( 9600 );
  // SSD1306_SWITCHCAPVCC = generate display voltage from 3.3V internally
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  // Show initial display buffer contents on the screen --
  // the library initializes this with an Adafruit splash screen.
  display.clearDisplay();
  drawStartup();
  // Clear the buffer
  display.clearDisplay();
  display.display();
  display.setTextSize(4);      // Normal 1:1 pixel scale
  display.setTextColor(WHITE); // Draw white text

  display.cp437(true);         // Use full 256 char 'Code Page 437' font
}

void drawStartup(void) {
  display.clearDisplay();
  for(int16_t i=0; i<display.height()/2; i+=2) {
    display.drawRect(i, i, display.width()-2*i, display.height()-2*i, WHITE);
    display.display(); // Update screen with each newly-drawn rectangle
    delay(3);
  }
  delay(250);
}

bool onoff = false;
void loop() {
  display.clearDisplay();
  while (gps.available( Serial )) {
    gps_fix  fix = gps.read();
    
    display.setCursor(3, 3);
    display.setTextSize(1);
    char buf[22];
    sprintf(buf, "(%02i) <%02i:%02i:%02i>", fix.satellites, fix.dateTime.hours,fix.dateTime.minutes, fix.dateTime.seconds);
    for (size_t i = 0; i < 15; i++) display.write(buf[i]); 

    char str_temp[6];
    sprintf(str_temp, "%03ikm/h", int(fix.speed_kph()));
    str_temp[5] = '\0';
    display.setCursor(6, 18);
    display.setTextSize(4);
    for (size_t i = 0; i < 5; i++) display.write(str_temp[i]); 
    onoff = !onoff;
    if (onoff) display.invertDisplay();
    display.display();
  }
}