The Raspberry Pi as a Stratum-1 NTP Server(satsignal.eu) |
The Raspberry Pi as a Stratum-1 NTP Server(satsignal.eu) |
I built an auto-install script that anyone here is welcome to use or reference[1]. If you know what you're doing, just change the GPIO pin to your PPS input and fire away.
Unlike the author I used Chrony instead of NTP. It's lighter-weight and much easier to configure with a PPS/GPS reference clock.
The GPS chip I used was an ATGM336H, which can be had for less than $8 on ebay. I'm able to lock consistently 11 satellites from my desk[2]
Keep in mind the Pi has no hw RTC. If you're doing this for fun spend a few more bucks and buy an rtc chip from ebay so you don't drift considerably between being powered off.
1. https://github.com/stephen-mw/raspberrypi/blob/master/roles/...
2. https://www.ebay.com/sch/i.html?_from=R40&_nkw=ATGM336H&_sac...
I've started buying SanDisk's "High Endurance" microSD cards hoping it will mitigate any such issues in the future, but I haven't had time to get the NTP set up again... I really should have cloned the image.
I think the hardest part was finding a case with space for the GPS hat[0] with an open end for the coax connector. The hat sits a bit crooked because of something bulbous on top (condensator?).
[0]: https://store.uputronics.com/index.php?route=product/product...
After the advice from a fellow HN reader [1] I bought a bunch of aMLC microSD cards from DigiKey. No S&H costs and it literally arrived 1,5 days later (from Springfield to The Netherlands) though I had to pay import tax. Needless to say, they've been rock stable. I'm using one in a Pi and one in a Dafang camera [2]. I still gotta replace the microSD cards in the remote Pi's though but I'll do it once they break (again).
a) eMMC which can use a tiny flash module of the same type flash as found in MLC SSDs, with flash controller chip for write wear leveling
or
b) M.2 NVME SSD interface such as can be found on 170x170mm mini-itx x86-64 motherboards for intel or amd single socket CPUs. And of course on larger motherboards as well.
c) the "traditional" SATA3 disk interface which can be used for a SATA3 interface SSD.
Due to the very limited write lifespan of microSD cards, even "industrial" ones, it's just a really bad idea reliability wise to use a microSD card for boot and OS storage on any sort of remote embedded system that does anything important.
The drive writes per day (DWPD) figure in GB for even a cheap $55 consumer grade MLC SSD is vastly higher than the amount of times you can write to a microsd card.
This is a big jump up price-wise on the 'Pi, but it meets your "32gb of storage" requirement for $174:
https://shop.udoo.org/other/home/udoo-x86-advanced-plus.html
Yes, it maybe old-style, but it's these sort of sites that the internet was originally built on. It's a real shame that they are becoming a dying breed.
That alone will negate any benefit of running a stratum 1. You lose the precision and accuracy over wifi. Jitter on intranet with the pi as a timesource would be magnitudes greater than the GPS link.
also, here's a writeup i did on my experiences creating something with an rpi 3 model b+:
https://github.com/stephenhu/written/blob/master/raspberrypi...
The real reason though, is because I can, and I like saying my computers are more accurate and precise than their phones.
1: https://www.friendlyarm.com/index.php?route=product/product&...
I have an RPi running on one of those tiny USB thumb drives that only protrude a few mm and it's running a data capture suite I wrote to monitor my internet connection which writes to a PostgreSQL database on the Pi.
I was hopeful that NextThing would get there, their C.H.I.P board was nice (when you could actually get them to sell you any) and had 8GB on-board, but they went tits-up earlier this year. Hardware is hard...