[time-nuts] First success with very simple, very low cost GPSDO, under $8
time at patoka.org
Mon Apr 14 16:27:11 UTC 2014
I was experimenting with the same setup for STM32 MCU. This
microprocessor has accept the sine wave from external OCXO or GPSDO. No
problem with this. The only thing: I was need to start MCU from slow
"watch" crystal first. And then switch it to work to external one. In
another case I got incorrect timing settings for MCU. Later, I decide to
implement LTC6957-3 chip to "share" REFCLOCK source, since that chip has
two equal CMOS-level outputs.
Unfortunately I have no tool to measure the phase noise and jitters on
> It turns out all of this is built into the AVR chip. There is a
> and logic to copy the current counter value to a register on a PPS
> raising edge. The counter keeps running and every second its value
> I can connect the OCXO and the PPS directly to the AVR pin. The AVR
> hardware (a fast comparator) to "square" a low amplitude sine wave and
> the counter on a zero crossing. So it looks like I can get rid of
> ALL of
> the external chips. The built in DAC is working well also but it
> some external resisters and caps.
> No need for '74 FFs or '373' or counter chips. I do get precision
> with no time critical software, no 74xxx chips.
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