The NEO-6M GPS module provides real-time coordinate acquisition for embedding in Morse transmissions. GPS is completely optional — the beacon works without it.

Hardware Connection

UART2 Configuration

Signal	ESP32 GPIO	GPS Pin	Notes
RX	GPIO 22	TX	GPS TX to ESP32 RX (input-only)
TX	N/C	RX	unconnected - firmware never sends to the GPS

Baud rate: 9600 (NEO-6M default)

Note

UART2 is started only when gpsEnabled = true in configuration.

NMEA Parsing

TinyGPS++ Integration

CODE

#include <TinyGPSPlus.h>

TinyGPSPlus gps;
HardwareSerial GPSSerial(2);

void initGPS() {
  GPSSerial.begin(9600, SERIAL_8N1, 22, 12);
}

void readGPS() {
  while (GPSSerial.available()) {
    gps.encode(GPSSerial.read());
  }
  
  if (gps.location.isValid()) {
    lat = gps.location.lat();
    lon = gps.location.lng();
    sats = gps.satellites.value();
  }
}

Payload Formats

Configuration Options

Config	Morse Message
Base only	`SOS`
Name only	`SOS DE MARIO ROSSI`
GPS only	`SOS PSN N4553 E01230`
Name + GPS	`SOS DE MARIO ROSSI PSN N4553 E01230`

GPS Coordinate Encoding

Truncated DDM (Degrees + Decimal Minutes x 10):

CODE

N4553 = 45 53' N (lat 45.883)
E01230 = 12 30' E (lon 12.50)

Info

This encoding is intentionally compact to minimize transmission time. Full decimal coordinates are logged to Serial at much higher precision.

GPS Boot Behavior

Boot Sequence

If gpsEnabled and no RTC fix cached: show GPS wait screen
Display satellite count and progress bar
Press MODE to skip wait at any time
If timeout elapses: transmit without coordinates
Once fix acquired: store in RTC RAM

Fix Quality

Condition	Payload
Fresh fix (< 3s age, >= 3 sats)	Current fix
Stale fix (RTC cache)	Cached fix (marked stale)
No fix + timeout	`PSN UNKN`

Configuration Parameters

Parameter	Default	Range	Notes
`gpsEnabled`	true	true/false	Enable/disable module
`gpsIncludeInBeacon`	true	true/false	Include in Morse payload
`gpsFixTimeout`	60s	10-120s	Max wait for fix at boot
`gpsMinSats`	3	1-10	Minimum satellites for valid fix

Tip

Press MODE during GPS wait to skip and transmit without coordinates. Useful when time is critical.

RTC RAM Storage

GPS fix is stored in RTC RAM to survive deep sleep cycles:

CODE

struct GPSState {
  double lat;
  double lon;
  uint32_t timestamp;
  uint8_t sats;
  bool valid;
};

RTC_DATA_ATTR GPSState lastFix;

Benefits

Coordinates available immediately after wake
No cold start delay
Last known position transmitted even without fresh fix

Serial Output

GPS Debug Messages

CODE

[      45][GPS  ] Waiting for GPS fix (timeout 30s)...
[   12400][GPS  ] Fix acquired: 45.53124  12.30456  sats=6
[   12401][INFO ] Payload ready: "SOS DE MARIO ROSSI PSN N4553 E01230"

Coordinates in Serial

Full decimal coordinates logged at higher precision:

CODE

[GPS] Location: 45.531243, 12.304567 (6 sats, HDOP=1.2)

Troubleshooting

Symptom	Cause	Fix
No fix after 2 min	Obstructed sky	Move outdoors
Fix timeout	Weak signal	Check antenna, wait 5+ min
Wrong coordinates	DDM format	`N4553` = 45 53’ N, not 45.53
GPS not starting	Module disabled	Enable in CONFIG portal

Warning

Cold start can take 5-15 minutes. Plan accordingly for alpine deployments.