Some people like to modify cars. Some like to overclock PCs. then there are the men like [Jack Zimmermann] who are consumed with precise time. He’s working on a job that will deploy NTP (Network Time Protocol) servers in different African countries as well as needed small, cheap, energy-efficient, as well as precise servers. What he wound up with is a extremely precise configuration for around $200. Along the way, he developed some customized hardware, as well as hacked a computer to sync to the GPS clock reference.
His original attempt was with a Raspberry Pi 3. However, the network adapter isn’t the fastest possible, both since it is 100 MBPS and, primarily, since it is linked through the USB bus. Network latency because of these limitations makes it challenging to serve precise time.
His service includes an Odroid C2. For $50 it is a extremely capable computer with four cores, gigabit Ethernet, as well as can even utilize eMMC storage which is quicker than the typical SD card. You can still utilize a traditional SD card, though, if you prefer.
For a time reference, [Jack] utilized a Trimble GPSDO (GPS-disciplined oscillator) that outputs a PPS (pulse per second) as well as two 10 MHz signals. These are locked to the GPS satellite clocks which are extremely precise as well as [Jack] states the timing is precise to within less than 50 ns. Unfortunately, the pulse from the Trimble board is as well short to read, so he developed a pulse stretching circuit.
Instead of trying to self-control the existing clock on the Odroid to the GPS reference, [Jack] eliminated the crystal as well as associated elements completely. He then utilized a frequency generator chip to convert the 10 MHz GPS signal to the 24 MHz clock the Odroid expects. He has plans to utilize the additional outputs from the chip to drive the ethernet as well as USB clocks, too, although their absolute accuracy is most likely not that critical.
We’ve seen NTP clocks before that can take in this type of time reference. If you want to understand much more about the Odroid C2, we talked about them at length last year.