Präzise GPS-Uhr: Günstige Genauigkeit & Zuverlässigkeit

Komponenten und Zubehör

Software

• Arduino IDE
• Bibliotheken: Adafruit GPS Library, LiquidCrystal_I2C, Wire, SoftwareSerial

Projektbeschreibung

Statt RTC-Modul oder NTP: **Zeit per GPS-Satelliten** aus NMEA-Sätzen parsen. GPS-Empfänger sind heute sehr günstig (hier GY-GPS6MV2 mit u-blox NEO-6M).

Vorab-Test (optional)

1. Windows: **u-center** (u-blox) installieren, GPS per FTDI-Adapter an COM-Port → Fix nach ~1 Min (rote LED blinkt)
2. NMEA-Strings in u-center (F8 Text Console) oder Online-Decoder prüfen: rl.se/gprmc

Schaltung

• GPS VCC → 5 V (Modul ist 3,3/5 V tolerant)
• GPS GND → GND
• GPS TX → Arduino Digital 8 (SoftwareSerial RX)
• GPS RX → Arduino Digital 7 (SoftwareSerial TX)
• LCD I²C: SDA → A4, SCL → A5 (Adresse oft 0x27 oder 0x3F)

Zeitzonen-Handling

NMEA liefert **UTC**. Lokale Zeit = UTC + Offset.

int timezone = +1; // Europa/Berlin (UTC+1)
// Im Code:
int hour = GPS.hour + timezone;
if (hour >= 24) hour -= 24;
if (hour < 0) hour += 24;

Windgeschwindigkeits-Anzeige (Beaufort-Skala)

GPS liefert Speed in **Knoten**. Umrechnung: **1 kt = 1,852 km/h**.

float speed_kmh = GPS.speed * 1.852;
if (speed_kmh <= 1)        "Windstille";
else if (speed_kmh <= 9)   "leiser Zug";
else if (speed_kmh <= 46)  "Brise";
else if (speed_kmh <= 56)  "starker Wind";
else if (speed_kmh <= 74)  "stürmischer Wind";
else if (speed_kmh <= 83)  "Sturm";
else if (speed_kmh <= 102) "schwerer Sturm";
else                       "Orkan";

LCD-Ausgabe (20×4)

• Zeile 1: Uhrzeit HH:MM:SS
• Zeile 2: Datum DD.MM.YY
• Zeile 3: Geschwindigkeit km/h + Beaufort-Text
• Zeile 4: Höhe (Altitude) in Metern

Update-Intervall: ca. 2 Sekunden. Für 16×2 Display: Sekunden & Höhe weglassen.

Arduino-Code (basierend auf Adafruit GPS Library Example)

// Test code for Adafruit GPS modules using MTK3329/MTK3339 driver
// modified 01.02.2020 - Ingo Lohs
// GPRMC & GPGGA decoder: https://rl.se/gprmc

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x3F, 20, 4); // Adresse anpassen (0x27/0x3F)

#include <Adafruit_GPS.h>
#include <SoftwareSerial.h>

SoftwareSerial mySerial(8, 7); // RX=8, TX=7
Adafruit_GPS GPS(&mySerial);

#define GPSECHO true
int timezone = +1; // Europe/Berlin

void setup() {
  lcd.init(); lcd.backlight();
  Serial.begin(115200);
  delay(5000);
  Serial.println("Adafruit GPS library basic test!");
  
  GPS.begin(9600); // UBLOX 6M Default
  GPS.sendCommand(PMTK_SET_NMEA_OUTPUT_RMCGGA); // RMC + GGA (Altitude)
  GPS.sendCommand(PMTK_SET_NMEA_UPDATE_1HZ);    // 1 Hz Update
  GPS.sendCommand(PGCMD_ANTENNA);
  delay(1000);
  mySerial.println(PMTK_Q_RELEASE);
}

uint32_t timer = millis();

void loop() {
  char c = GPS.read();
  if (c && GPSECHO) Serial.write(c);
  
  if (GPS.newNMEAreceived()) {
    if (!GPS.parse(GPS.lastNMEA())) return;
  }
  
  if (timer > millis()) timer = millis(); // Overflow-Schutz
  
  if (millis() - timer > 2000) {
    timer = millis();
    
    // Serial Debug Ausgabe
    Serial.print("\nTime: ");
    // ... formatierte Zeit, Datum, Fix, Location, Speed, Angle, Altitude, Satellites ...
    
    // LCD Ausgabe
    lcd.setCursor(5, 0);
    int hour = GPS.hour + timezone;
    if (hour < 10) lcd.print('0');
    lcd.print(hour, DEC); lcd.print(':');
    if (GPS.minute < 10) lcd.print('0');
    lcd.print(GPS.minute, DEC); lcd.print(':');
    if (GPS.seconds < 10) lcd.print('0');
    lcd.print(GPS.seconds, DEC);
    
    lcd.setCursor(5, 1);
    if (GPS.day < 10) lcd.print('0');
    lcd.print(GPS.day, DEC); lcd.print('.');
    if (GPS.month < 10) lcd.print('0');
    lcd.print(GPS.month, DEC); lcd.print('.');
    lcd.print(GPS.year, DEC);
    
    if (GPS.fix) {
      lcd.setCursor(0, 2);
      float speed = GPS.speed * 1.852;
      lcd.print(speed, 1);
      
      // Beaufort
      if (speed <= 1) lcd.print(" Windstille");
      else if (speed <= 9) lcd.print(" leiser Zug");
      else if (speed <= 46) lcd.print(" Brise");
      else if (speed <= 56) lcd.print(" starker Wind");
      else if (speed <= 74) lcd.print(" stuerm. Wind");
      else if (speed <= 83) lcd.print(" Sturm");
      else if (speed <= 102) lcd.print(" schwerer Sturm");
      else lcd.print(" Orkan");
      
      lcd.setCursor(0, 3);
      lcd.print("Hoehe: ");
      lcd.print(GPS.altitude);
    }
  }
}

Hinweis zu DCF77

In Europa auch DCF77-Funkzeit möglich, aber teurer & empfindlicher. GPS ist kostengünstiger & weltweit nutzbar.