ESP32 NTP Server

NTP time server implementation using NEO-6MV2 GPS module as a reference clock. Originally based on https://github.com/sigorilla/arduino-ntp-server, with heavy modifications to work on espressif ESP32 platform, and to use the global positioning system (GPS) instead of the russian GLONASS. The GPS is re-configured for 115200 baud and 1 PPS with 100ms pulse duration at run-time. The rewrite also incorporates a forked version of the well-know "time.h" arduino library modified to provide microsecond resolution and the ability to use a PPS clock input signal. Specifically, the code is designed to run on an "olimex ESP32-GATEWAY" development board having an on-board RJ45 100MBit ethernet jack, but can easily be adapted to work with other ESP32 boards using external ethernet connectivity (or WiFi connection). Also, a cheap 128x64 0.96" Oled LCD is used for displaying basic information. Average precision was measured (by comparison to known-good time sources) with 1 ms, or 0.001 seconds (the smallest reliable time unit this GPS module can deliver) offset compared to e.g. the PTB NTP server ptbtime1.ptb.de, or other official time sources, provided the offset is adjusted accordingly using #define TIME_OFFSET_USEC. The NTP server uses DHCP for IPv4 address retrieval, and replies to "simple mode" NTP queries by sending packets with "stratum 1" flag (testable with w32time.exe on windows: w32tm.exe /stripchart /computer:<IP-of-NTP-server> /period:1 /samples:3 /packetinfo, or with ntpdate on linux: ntpdate -q <your-NTP-server-IP>). GPS reception is good even indoors when using an external GPS antenna instead of the small ceramic antenna shipping with commonly sold GY-NEO6MV2 modules. Precision can be further improved when using one of the more expensive "NEO7T"/"NEO8T" modules (note the "T"), which allow for fixed location precision timing modes to be used, giving a PPS pulse with superior accuracy.

Used Hardware

• Microcontroller: Olimex ESP32-Gateway
• GPS time reference: GY-NEO6MV2
• OLED: cheap 0.96" OLED
• Antenna: active GPS antenna with 5m wire

Wiring

GPS <-> ESP32
-----------------
GND --> GND
Tx  --> PIN10 (Rx)
Rx  --> PIN32 (Tx)
VCC --> +3.3V
LED/PPS output --> 600 ohm resistor --> PIN36  
(this needs some fine soldering with thin wire to attach PIN36 to the trace running to the GPS module LED)

Links

• u-center software
• u-blox command reference manual
• NTP packet reference