[time-nuts] Frequency counter questions
tshoppa at gmail.com
Mon Apr 24 07:28:47 EDT 2017
Jerry, for a 100MHz PIC based counter a prescaler will be necessary. But it will not be necessary for a 30MHz counter.
Prescalers do not have to be by divisors of 10. I recall the PIC counter input to be good to 50MHz so the prescaler could just be a divide by two if you need a 100MHz counter and it *has* to be done by a PIC.
Of course there are lots of logic families that don't need a prescaler at 100MHz and could be used to make a frequency counter.
Most frequency counter designs out there on the net introduce an extra count or two due to flawed conception of gate.
Sent from my VAX-11/780
> On Apr 23, 2017, at 9:25 PM, Jerry Hancock <jerry at hanler.com> wrote:
> For some reason I am not getting the individual emails so I apologize for not replying more promptly. I’ll have to check my profile.
> As far as I can tell from the notes, and by the way, the number of notes was why I was trying to move this off list, to get to .001hz I need to measure over 1000 seconds. This is ok. Since I am looking for an average over time anyway, this is not a problem. By the way I am using a GPSDO and planned to use it divided down for the gate.
> The only reason I mentioned a prescaler was that there was a 12 digit counter schematic on the web that looked pretty complete. This person used a prescaler and I was trying to wrap my head around how this helped with resolution and I guess from the replies, that is not a practical solution (using a prescaler) when you want high resolution unless I use the inverse operation which I can’t remember what it is called off the top of my head.
> I’ve seen some HP 12 digit counters but since I have a GPSDO and who knows how many micro development boards around here, I thought I would take a run at it.
> So to summarize, if I limit my high resolution to 99,999,999.999hz and use a gate of 1000 seconds, would that get me to .01hz? If not, then what would the possible resolution be?
> Thanks for all the input, very helpful.
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