Assuming you are counting every cycle with no pre-scaler and can't measure the period, the answer is easy.
If you want to measure Hz then the gate needs to be 1 second. If you want to measure too 0.1 Hz then you need a 10 second gate. In your case 0.001 Hz you need to count for 1,000 seconds. If you use a prescaler let's say it is a "divide by N" then you multiply the gate time by N. If the frequency is high and you want to measure to .001 Hz then you need a really large maximum count and will overflow a 32 bit integer You want 12 digits so you need to use a 64 bit integer counter. The STM32 has some pre-scalers built in and a built in counter too, I think. I don't know what their maximum speed is. You don't need the compute power is an STM32 but "why not" as they cost only $12, I use the Nucleo boards and mbed. The problem with counting to 12 digits is that you are only measuring the average frequency over a very long interval. The signal is likely not that stable. Lets say during that 10 second gate the signal was DC or zero Hz for 5 seconds then went to 2 MHz. You meter would read 1.000 MHz but the signal was NEVER 1 MHz. The OTHER way to measure frequency is harder but faster. You measure the period. A perfect meter could mere the unknown frequency in one cycle. It would not be an average. But there are no perfect meters. On Sun, Apr 23, 2017 at 12:14 AM, Jerry Hancock <je...@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 > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.