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A collection of 27 posts

ntp

APU2 NTP server

I bought an apu2c0. I believe it will make a better NTP server than my other NTP servers.

  • Dan Drown
3 min read
ntp

RK3328 based NTP server

I got a ROC-RK3328-CC SBC because it has true gigabit ethernet, emmc, and USB3.  These are all better I/O options than the latest Raspberry Pi 3 B+. I put a SATA hard

  • Dan Drown
3 min read
gps

GPS module measurements, part 3

GPS module comparison: NEO-7N vs NEO-M8N

  • Dan Drown
3 min read
gps

GPS module measurements, part 2

After the previous tests, I ordered another GPS antenna to improve the signal conditions. They're just the cheap puck style antennas with SMA connectors ($10 on Amazon), and I've put them on my

  • Dan Drown
3 min read
gps

GPS module measurements

Starting point I got a u-blox NEO-6M and I wanted to compare it to my NS-T. Since I don't have a frequency counter, I decided to try creating one myself. The hardware I

  • Dan Drown
4 min read
ntp

PPS over USB

Goal For keeping your system clock on time, you can't beat the Pulse Per Second (PPS) signals available from $10 GPS modules. They typically have better than 100 nanosecond accuracy. GPIO PPS is

  • Dan Drown
4 min read
time

Frequency synchronization without phase in NTP

I've been working on my high accuracy RTC project. Here's a picture of one of the two systems: Connections The TCXO devboard, BME280, and PCF RTC are all on the i2c bus. The

  • Dan Drown
4 min read
rtc

RTC comparison

Real Time Clocks I bought two high accuracy RTC (real time clock) modules and wanted to compare them. RTCs are useful for very low power clocks. They can run for years off of

  • Dan Drown
3 min read
ntp

GPS PPS drift when it has no signal

Question: What happens to a GPS receiver's pulse per second (PPS) when it loses signal for a long time? To answer this, I first moved the antenna away from the window and put

  • Dan Drown
3 min read
gps

Beaglebone Cape for NS-T, revision 2

I'm testing the second revision of this cape now. Schematic is on github (left: rev1, right: rev2) It's working much better than rev1, but time will tell if it has the same frequency

  • Dan Drown
1 min read
gps

Update on Beaglebone Cape for Navspark NS-T

The cape has been running for 5 days now. I've been tweaking the system to see if I can get it stable. So far, the local clock looks like this: The red line

  • Dan Drown
2 min read
navspark

Beaglebone Cape for Navspark NS-T

Goal My next goal in the quest for a better NTP server is to improve the TCLKIN source. Previously, I was experimenting with TCXO's. I bought a Navspark NS-T (a timing-grade GPS receiver)

  • Dan Drown
3 min read
gps

TCXO + Beaglebone Black, part 2

Starting from the previous TCXO modification, I wanted to get a 24MHz TCXO working. Trial #1 I bought a set of three undocumented 24MHz TCXO's off ebay for $6. I was hoping that

  • Dan Drown
4 min read
navspark

TCXO + Beaglebone Black

I've added support for an external clock (TCLKIN) to the Beaglebone Black timer driver. Setup I used what I had on hand to test it. I setup a Navspark microcontroller to send a

  • Dan Drown
2 min read
gps

Beaglebone Black timer capture driver

More info on: Hardware, Kernel Driver software The Beaglebone Black has a hardware timer capture. This means it can save the couter value at the time an input edge happens. Since it has

  • Dan Drown
2 min read
gps

Beaglebone Black GPS+Temperature cape

I moved my Beaglebone Black GPS+Temperature setup from a breadboard to a proto cape. The soldering isn't great, and the wire I had on had was much too thick for this. The

  • Dan Drown
1 min read
gps

Beaglebone Black NTP/GPS Server, Temperature Compensation part 2

See the Part 1 of Temperature Compensation or the hardware setup Overview In part 1, I did a trial run of chrony's temperature compensation and got a pretty good result. In this part,

  • Dan Drown
2 min read
gps

Beaglebone Black NTP/GPS Server, Temperature Compensation part 1

See also: The hardware/software setup or part 2 Overview Chrony (the NTP server software) has temperature compensation built in, using a quadratic forumla to estimate the effect of temperature changes have on

  • Dan Drown
3 min read
gps

Beaglebone Black NTP/GPS server

Goals I wanted to experiment with using temperature measurement to augment a NTP stratum 1 server. I started with a very similiar setup to this one. [Edit: the8thlayerof.net is gone, link changed

  • Dan Drown
3 min read
gps

Stratum 2 NTP over a Cable Modem

Goals I have a Stratum 1 NTP server at home, and ideally I'd like to join the ntp pool as a server. The problem is, my home connection isn't up to this task.

  • Dan Drown
3 min read
navspark

Measuring Asymmetric latency via NTP, part 3

Part 1, Part 2 Varying round trip times Asymmetric latency changes NTP's calculated clock offsets. What do the offsets look like when two clocks are in sync (or always within ~200us) and the

  • Dan Drown
2 min read
navspark

Measuring Asymmetric latency via NTP, part 2

See the first part for the math Let's use a third party (stratum 2) observer to compare the stratum 1 NTP clocks. Round trip times First, a graph of the $rtt times from

  • Dan Drown
2 min read
navspark

Measuring Asymmetric latency via NTP

Goal Learn more about the latency characteristics of my cable connection. Starting point I have a stratum 1 NTP server at home. Below is a graph of its performance. The offset between the

  • Dan Drown
4 min read
navspark

Navspark NTP stratum 0 clock

Project Goal I want to create a stratum 0 NTP clock that does not require soldering or any special hardware. It should only require a USB port and software. It should have at

  • Dan Drown
2 min read
arduino

Navspark UART/USB bridge

I created a program on the Navspark to send characters at 150 microsecond intervals and then received them on a PC. Below is a histogram of how long it took between characters: The

  • Dan Drown
1 min read
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