You only need ONE inverter gate. The purpose is the flip the pulse. The MAX 232 chip flips the logic once which works fine for the data but you need to flip the control lines (maybe if the GPS reciever did not already do this for you.)
Flipping the PPS has the effect of moving the pulse by the length of the pulse so one gate in this case will move the pulse by 100MS. On Sat, Sep 7, 2013 at 9:22 PM, Bob Bownes <bow...@gmail.com> wrote: > 100ms is an awful lot of 'inverter gates'! > > On Sep 7, 2013, at 23:15, Chris Albertson <albertson.ch...@gmail.com> wrote: > >> With RS232 the data uses negative logic (low is "1") and the control >> lines use positive logic (high is "1".) That is, a control line is >> "asserted" when it is at logic 0, a positive voltage. >> >> Some one at one time must have thought this made sense. >> >> The good news is that a mistake is easy to detect and fix. If the >> pulse is 100MS long and you have it inverted then your time will be >> off by 100MS. When you are designing the board put in some extra >> inverter gates >> >> On Sat, Sep 7, 2013 at 7:15 PM, Mark Sims <hol...@hotmail.com> wrote: >>> I got in those Adafruit GPS boards. They are a very nice little GPS. >>> VERY sensitive. I could get good lock indoors on my (windowless) kitchen >>> floor. The house is 2 story, stucco with wire mesh in the stucco. I >>> could also get lock in a restaurant that had a tin roof. We were far from >>> any windows. >>> The 1PPS signal is normally low and pulses high for 100 milliseconds. The >>> RS-232 adapter board that I built feeds this into an RS-232 transmitter >>> chip (MAX3232), so on the interface connector CD will be at +V and pulse >>> down to -V. Is this what stock NTP likes? >>> Also, I laid out the adapter board so it an accommodate a Trimble >>> Resolution T or a Crius CN06 receiver. The Crius receiver uses a U-Blox >>> NEO-6M receiver. They can be had for around $22 at HobbyKing. They seem >>> to perform even better than the AdaFruit module. It looks like you will >>> need to bodge a wire onto the TIMEPULSE pin to use it for 1PPS. >>> _______________________________________________ >>> 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. > _______________________________________________ > 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.
