[time-nuts] ADC sample voting algorithm?

Nick Sayer nsayer at kfu.com
Wed Oct 5 20:22:06 EDT 2016

> On Oct 5, 2016, at 5:00 PM, Bob Camp <kb8tq at n1k.org> wrote:
> Hi
> What does the signal you are sampling look like? 

The last time I actually looked (it was a while ago), it looked reasonable as closely as I could look, but the ADC resolution is something like 1mV per LSB, and I’m not sure I looked that closely.

> Does it (maybe) have a bit of noise on it?
> If it is the output of a “normal” TDC, then the answer is to sample once.

I dunno about a “normal” one… This one is the one I got from Jim Harman. The phase difference between the divided-by-10 output and PPS goes through a diode, JFET and then an RC (with a much higher discharge resistor).

As long as you sample at least 1 µs after the PPS (and it takes at least that long to get into the ISR anyway), it *ought* to be stable for dozens of µs.

That’s kind of why I’m going down the road of multiple samples - to see if there’s anything to it.

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