ESP8266 GPS-backed NTP Server (NEO-6M, no PPS) + Web Status

A small NTP server based on an ESP8266 D1 mini (AZ-Delivery) that gets its time from a u-blox NEO-6M GPS module and provides it to your local network via NTP (UDP/123). It also exposes a simple HTTP status page so you can verify GPS/NTP without needing a USB serial connection.

Note: Without a 1PPS (pulse-per-second) signal, accuracy is limited. Typical offsets are in the range of a few 10–100 ms (Wi‑Fi jitter + NMEA latency).

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Features

• NTP server on UDP port 123
• GPS time from NMEA RMC (date/time) and NMEA GGA (fix/sats/HDOP)
• GPS output configured via UBX: only RMC + GGA enabled, other NMEA sentences disabled
• Web status page at http://<ESP-IP>/ showing:
  • haveTime / GPS UTC date & time
  • Fix status, satellites, HDOP
  • Last received NMEA lines (Raw / RMC / GGA)

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Hardware

• AZ-Delivery D1 mini (ESP8266)
• NEO-6M GPS module (e.g. GY-NEO6MV2, pins labeled VCC RX TX GND)
• Optional external GPS antenna (often improves reception)
• USB power supply / power bank (useful if the GPS must sit by a window)

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Wiring

D1 mini ↔ NEO-6M (module pins: VCC RX TX GND)

NEO-6M Pin	D1 mini Pin	Notes
VCC	5V (or 3V3)	Many GY-NEO6MV2 boards include an LDO and accept 5V
GND	G / GND	common ground
TX	D5 (GPIO14)	GPS TX → ESP RX
RX	D6 (GPIO12)	GPS RX ← ESP TX

Important: TX/RX must be crossed.

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Software / Setup

Arduino IDE

1. Install the ESP8266 board package (if you haven’t already)
   Additional Boards Manager URL:
   http://arduino.esp8266.com/stable/package_esp8266com_index.json
2. Select the board:
   Tools → Board → ESP8266 Boards → “LOLIN(WEMOS) D1 R2 & mini”
3. If upload issues occur, set Upload Speed to 115200
4. Install libraries (Arduino Library Manager):
   • TinyGPSPlus

Wi‑Fi credentials

Edit in the sketch:

const char* WIFI_SSID = "...";
const char* WIFI_PASS = "...";

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Usage

1. Flash the sketch.
2. Place the ESP + GPS where reception is good (often near a window) and power it.
3. Find the ESP IP address in your router’s client list (or via Serial Monitor at 115200).
4. Open the status page:
   http://<ESP-IP>/

When everything works you should see:

• haveTime: YES
• gps.time valid: YES
• gps.date valid: YES
• satellites > 0
• last RMC/GGA lines present

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Testing NTP on Windows (GUI)

Example: NetTime (standalone GUI)

• Add your ESP IP (e.g. 192.168.1.18) as a time server
• For testing, disable/remove other servers so only the ESP is used
• Click Update Now
• Status should become Good and show offset/lag

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Troubleshooting

Status page shows haveTime: NO and no NMEA lines

• TX/RX swapped (most common) → GPS TX → D5, GPS RX → D6
• Wrong baud rate (usually 9600, sometimes 38400)
• Check power (5V vs 3V3)
• No GPS reception indoors → move closer to a window / outside

NTP client cannot reach the server

• Ensure haveTime: YES (server replies only when time is valid)
• Check router/AP “client isolation” settings
• Check Windows firewall as a quick test

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Accuracy / Limitations

• Without PPS the time is derived from NMEA sentences, which adds latency/jitter.
• Wi‑Fi adds additional variable delay.
• For best accuracy you need a GPS module with 1PPS connected to an interrupt pin and proper time discipline (not part of this project).

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License

MIT