[time-nuts] Maxim DS1342

mc235960 mc235960 at gmail.com
Tue Nov 12 03:47:08 EST 2013


Le 12 nov. 2013 à 03:13, Chris Albertson a écrit :

>> You want to drive the RTC with an external PPS to get time/date into an
>>>> Arduino?
>>>> Why not feed the PPS to the Arduino and have it compute date and time?
>>>> 
>>>> It is really not that hard to count seconds. You don't really need an
>>>> external chip to do that.
> 
> 
> Typically you need more fine time resolution them just a seconds counter.
> Especially if you are using an Arduino, you are maybe building a robot or
> real-time controller and want to measure something like "Milliseconds per
> revolution"  so you need a faster running counter and then you want to
> calibrate that counter
> 
> A typical method is to have the PPS trap the faster counter, than you can
> see how many periods per second your counter is moving.  You can mount for
> a 1,000 seconds and get a pretty good idea.  Then you use the fast counter,
> now that you know it's rate for you timing.
> 
> So you don't need an external chip if you are willing to track the rate of
> the free running clock.
> 

  True, if you don't need to know what your epoch is.  Although the DS indicates GPS PPS is a choice for the reference, why bother as you get your date and time to a better resolution on first fix than any RTC is going to give you. The advantage of this chip I think, is that if you have a reference, you get to keep time with much better resolution than a normal RTC without GPS. If I am interpreting the DS correctly, the 1Hz out is held within 7,8ms of the reference, which is pretty good over very long Tau. Maybe the key is that one of the accepted references is 50/60Hz  power line frequency. That nets billions of end users.


> -- 
> 
> Chris Albertson
> Redondo Beach, California
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