GPSNTP

This is a pair of dev boards designed to provide a local stratum 1 GPS based NTP server.

• ESP32-S3-MINI-N4-R2 (Dual CPU, 4M flash, 2M RAM)
• 10/100 Ethernet
• PoE option, but can also be powerd by USB-C
• 12 LEDs showing GPS status (number of sats on each network and PPS blink)
• L86 GPS module, with CR2032 battery holder (CR2032 recommended)
• WAGO connectors for connecting cable from main module to GPS
• Optional click output (pads on board connect to piezo sounder - GPIO 0 can toggle on every request)

The power supply flexibility is also a key feature, either USB-C, or PoE. PoE requires the Ag9912-LP module (optional extra).

The 12 LEDs are WS2812, and the supplied code shows them lit in sequence, blue for NAVSTAR(GPS), red for GLONASS, and green for GALILEO, with one LED for each 2 active satellites in use (half brightness for final odd number). The last LED blinks yellow for each PPS on the second.

Unlike some GPS devices, which have a coax to a patch antenna, the GPS module connects via 5 cores to the main board, allowing it to be placed outside. Solid core cat5 cabling works, but screened cable may be better in some cases. Cable can easily run several metres. You should ensure the GPS module has a good view of the sky for best results. For outside placement we find these work well https://weatherspares.co.uk/products/ecowitt-rs0001-sensor-shelter

This a fraction of the price of typical commercial GPS NTP servers. These commercial units claim 100,000 requests a second, where as this is a few thousand. This response time can be down to 0.1ms. A typical, even large, business, would not have any where near that many requests per second, so this is ideal as a business time server, but not so much as a high volume NTP pool server. Of course this could work as the main reference for a device that operates as a stratum 2 server, such as a FireBrick, and provide high levels of requests per second. That said, the NTP pool is very flexible, and people are deploying these as lower volume pool servers already.

Supplied with resin 3D printed case for board and for GPS module. You'll need a lead - solid cat5 is a good choice. Note the resin case will yellow in sunlight.

MQTT reporting shows status, PPS reliability, requests per second, location, etc.

Performance

Whilst these are designed for home/office use, which will have low requests per second, they have been deployed in the UK NTP pool where they have shown a score of 20 (maximum), and handling up to 5,700 requests per second.

Latest code includes a rate limit option which uses a source IP hash rate limit of 1 request per second. This is mainly aimed at relflection attacks (which are not that common as they do not amplify traffic, so are pretty pointless).

Tips

GPS

The GPS module needs a CR2032 battery to work. Boards have pads marked "No bat" that can be bridged to operate with no battery. A battery is recommended else startup takes a long time to get a lock, especially if not a clear view of the sky. This also applies on first use even with a battery, so be patient.

The GPS module should be placed facing up, not sideways, for best results. A good view of the sky is recommended, but it will generally work fine on the side of a building. We have placed these outside in the summer sun and they seem to cope well.

The resin case is not waterproof - if placed outside then it is better to enclose in a suitably sealed plastic box or similar. It can often work inside a window or inside a loft under the roof tiles.

See the status web page shows details of number of satellites in use.

PoE

The PoE module is optional. It is a simple leaded module, so easy to solder. When soldering to the board check pin 1 carefully. It has a small 1 mark on top of module, and PCB has a 1 by pin 1.

PoE requires a current draw to stay powered. Some switches are happy with lower current, so try turning off the ethpoepwm - if that works it saves power and heat.

Without PoE you need separate power, such as USB-C.

Ethernet

The device can use WIFi and Ethernet. The Ethernet works with or without PoE.

Normal working operates Ethernet as a full network interface allowing access to the web control pages, MQTT, etc. Response times for NTP are around 2ms.

However, you can set gpslowlatency which switches the module to a special NTP only Ethernet working. This starts after 2 minutes and when there is a GPS lock. In this mode normal Ethernet working is suspended, so you will have to use WiFi to access control pages, MQTT, etc. The Ethernet IPv4/IPv6 are frozen, so recommended to use fixed IP config if your DHCP server would be upset by IP used after expiry. However the NTP latency drops to around 0.1ms.

If your are trying to maximise requests per second it is worth putting the device on its own Ethernet segment/VLAN with minimal other devices on the same subnet. This reduces stray broadcast packets which all take up SPI bandwidth.

All parcels shipped with tracked shipping, usually shipped within one working day. If you find a large order has no shipping to EU, try placing smaller orders under €150.