[time-nuts] Frequency counter questions

Bob kb8tq kb8tq at n1k.org
Sun Apr 23 10:38:32 EDT 2017


Counting 12 digits is relatively easy, if that is the only constraint. Bring your “signal” into one of the 
timer clock inputs on the MCU. If your “signal” is 10 MHz that will be simple. If it’s 30 GHz it will be
more difficult. 

10 MHz gives you 7 digits a second. To get to 12 digits, you need 100,000 seconds. Roughly speaking,
your counter “gate time” would be one day.  If your input is 1 MHz, your “gate time” would be 10 days.

My *guess* is that there is a disconnect between what you want to do and what I’m hearing you want to do.


If you want to do something like the 53131 or even the 5335, you will need something a bit different 
than the F7 to do it. They are wonderful MCU’s but not really fast enough to do the fancy stuff.


> On Apr 23, 2017, at 3:14 AM, Jerry Hancock <jerry at hanler.com> wrote:
> Hello,  I would like to find a person that would be able to answer some frequency counter questions I have.  
> Basically, I am thinking of building my own using one of the high end STM32F7 boards as the counter.  I would like it to count reliably to 12 digits (e.g. 30,000,000.001x hz).  I am not worried about input conditioning as I have a circuit that is suitable for my needs.  Most of my questions have to do with using a prescaler on the front (divide by N where what is N) to get to the desired resolution when using multiples of the PPS coming from my GPSDO.  Gate times could be as long as needed to get the resolution.  So what prescaler do I need and what gate time is required are the first two questions.  I suggest if someone is willing to help that they either reply here with an email address or send a note to meters at hanler dot com.  This is for my own non-commercial use.
> Thanks!
> Jerry 
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