Group, Seems to me that what's needed here is a current source for linear volts vs. time and the cmos switching to control the duration of the capacitor charge while the phase flip-flop is on. When it turns off, it interrupts the processor and isolates the capacitor so it acts as a sample-and-hold device. The processor can take its own sweet time reading the capacitor voltage (although this sets minimum limits on the pulse duration). When the reading has been captured, the micro toggles a FF that shorts the capacitor with a cmos switch. The short is removed when the phase FF toggles on.
This is a lot of analog circuitry, but it will operate as fast as the parts are capable of switching and not at the whim of whatever the micro is doing. Hope that's useful. Probably already been done. Bill Hawkins -----Original Message----- From: Magnus Danielson Sent: Tuesday, September 22, 2015 3:32 PM Jim, I had the intent to try this, but never got around doing it. Thanks for reminding me. Please share any enhancements. I did exchange some emails with Lars, but as that project never got off the ground, it faded out. Cheers, Magnus On 09/21/2015 10:02 PM, Jim Harman wrote: > Hi Can, > > For a simple analog solution, you might try a 74HC4046 phase detector > followed by a diode and RC network as used in Lars Walenius' GPSDO, > described here in the archives: > > https://www.febo.com/pipermail/time-nuts/2014-February/082820.html > > The phase detector produces a pulse whose width equals the time > difference between the two pulses. The RC network converts this to a > voltage proportional to the time difference, which you then measure > with the MCU's A/D converter. Using the rising edge of the signal at > pin 14 as the interrupt source triggers the A/D converter at the end > of the pulse, which corresponds to the peak of the analog signal.. The > 1 meg resistor discharges the capacitor between pulses. > > Lars' code also includes a filtering algorithm which does a nice job > of controlling one of the oscillators to match the 1-PPS generated by the GPS. > I have enhanced this if you are interested. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
