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Lars DIY GPSDO with Arduino and 1ns resolution TIC

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lars:
Yet another DIY GPSDO! On the internet you can find a lot of DIY GPSDO designs. What are the differences between them? Why this?
Some + and – I can come up with for mine:

+ 1ns resolution TIC (Time Interval Counter)
+ PLL (not FLL)
+ Uses Arduino (ok some might say it is negative)
+ Low parts count and cheap components
+ No need for a specific GPS receiver only requires 1PPS in
+ Easy adaption to different oscillators (from simple VCXO to Rubidium)
+ Configuration for VCO range, time constant (4-32000s) and a lot of other parameters
+ Outputs time error (ns), DAC value and temperature (and a lot of other information) to the serial port
+ Logs time error, DAC value and temperature every third hour
+ Stores last DAC value for use at power-up
-DAC resolution (now 16bits) and stability could be better
-No saw tooth correction
-No adaptive time constant
-Not using information from receiver e.g. number of satellites etc.
-No standardized communication protocol like many commercial GPSDO’s
-No display

Why did I do this? Since about 2010 I have developed my GPSDO. It started just because I was lazy and tired of tweaking my 10MHz house standard. The only thing I am proud of is the 1ns resolution TIC. A couple of years ago I published an old version on the time nuts forum. This time I decided to use this forum instead as I think my DIY GPSDO is something for experimenters in this forum.

For me it is perfect for experiments. I have learned a lot during the years I have used it (and developed it).

I have built several complete GPSDO’s but now the only one I have running continuous is a rubidium based DIY Arduino GPSDO I use as a lab standard for my instruments. That Rb GPSDO has been running almost continuous for more than five years with different versions of my Arduino software.

Today you can get a GPS module + antenna for about 10USD from eBay, an OCXO for 10-20USD, a metal box and connectors for about 10USD, the Arduino pro mini and all other components for about 10USD, So around 50-60USD should be enough to get all components for a complete GPSDO.



As I had problems with file extensions I added .txt to the arduino sketch .ino. You have to take away the .txt and place it in a folder with the same name. To easier read the file without arduino see the .txt without .ino in the file name.

I also had to divide the instruction as it was about 2MB. Sorry for the inconvenience.

Lars

lars:
Pages 8-18 of instruction

lars:
Last pages 19-21

Lars

Gyro:
An impressive looking design Lars. Thank you for sharing the full details and code.  :-+

Given the very low circuit complexity and cheap arduino based implementation (I think it is a positive), it would be hard to find a reason not try it out. Time to modify my messy LEA-6T 100kHz PLL breadboard.

jpb:
Thanks for publishing your design and experiences.

I have a long term project to produce a GPSDO but have got side-tracked on trying to improve my ADEV measurements (so I can select OCXOs). Also I keep changing my design approach which is half the fun.

I was interested to see that your currently run a rubidium full time - is this on all the time are just when you need it? I was leaning towards using an OCXO rather than rubidium because of better phase noise, lower power consumption and longer life. I have a couple of rubidiums but I wouldn't like to run them 24x7 for years because I'm not sure how much lamp life is remaining.

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