03 September, 2020

GPS corrected 10 MHz reference

My  GPS corrected 10 MHz reference now plays beautifully, as I finally was able to continue the project after a long break. All the parts were here already in February, but projects don't always develop as planned. I ended up with a modification of the F2DC Versatile Low Cost GPS Corrected Frequency Standard. It consists of an Arduino Nano, a Si5351 I2C configurable clock generator, and a GPS where the 1 PPS pulse is used to correct the frequency every 40 seconds.

My modifications were these:

  • LCD is controlled over I2C. The downside of that is that it seems no longer to be possible to display GPS time continuously
  • Rotary control for adjusting backlight of LCD
  • Display of GPS baud rate as it waits for the GPS signal
  • Error is shown in E-7 (rather than E-8) as then it corresponds directly to Hz at 10 MHz
  • 3D printed front with cut-out for the 16x2 LCD
  • Updated for the new NT7S Si5351 library (in the meantime an update also came on the F2DC website)
  • Initial correction value for my Si5351 needed to be much larger than F2DC's values. A value for calfact = 28000 was needed (others have also needed such large values as described on the F2DC website)

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