On Sun, Apr 23, 2017 at 6:25 PM, Jerry Hancock <je...@hanler.com> wrote:
> > > 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? > It is best to keep this kind of discussion on the list. That way if some one like me sys something dumb, it will get noticed and called out. OK, so it seems you (1) are interested in measuring frequency up to 100 MHz but no higher. (2) want to use an STM32 ARM uP to (3) Are using the older (and simpler) design that simply counts cycles and divides by the gate time to measure frequency If the above assumptions are wrong. STOP reading now and post corrections or additions OK so we are good to go.... I assume you know about and intend to use the built in counter/timmer on the STM32. You first step is to find out the maximum pule rate you can place on that pin. Lets guess it is 48 MHz. But you are a conservative engineer an want to de-rate it to 24 MHz. This means to measure up to 100 MHz you will need a prescaler that can divide by 4. This will transform you maximum 100 MHz to a maximum of 25 MHz. It will force you into using 4X longer gate time. This is the only reason to pre-scale, because you can't otherwise process the signal. Now it is very simple. You write software that starts the counters on the desired pin and then your GPS sends a signal every one second (You do NOT need to divide down the 10MHZ from a GPSDO because the GPS already has a one pulse per second output that feeds the DO.) SO every one second you read the number of counts and keep doing this for as many seconds as you need After the gate time which might be one second or 4,000 seconds you add up all the one second readings and compute the answer. Actually you can do better given the excess computer power you have: You can output a frequency estimate after the first send and then each second you can output a more accurate value until finally after 4,000 seconds out have 0.001 Hz. So in the first second you put up a display that is good for +/- 4 hZ and then four seconds later you can be a 1.0 Hz and after an hour 0.001 Hz As I wrote before. I use the "trigger" output of my old Tektronix scope as input to my counter because the scopes trigger is MUCH better. If you own a 'scope this will save you a LOT of work as all you would need to build is a voltage converter to take the trigger output to 3v3 volts for the STM32. The STM already can do rescaling and counting. Connect an I2C display and you are done with the hardware. For a better and cheaper display, the STM32 can serve a web page and then you see the frequency on your phone. 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.