[time-nuts] NTP/1-PPS/RS232 question

[Bob Bownes]

100ms is an awful lot of 'inverter gates'! 

On Sep 7, 2013, at 23:15, Chris Albertson <albertson.chris at 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 <holrum at 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.
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> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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