[time-nuts] help

[Mike Cook]

> Le 2 mai 2016 à 03:14, Chris Albertson <albertson.chris at gmail.com> a écrit :
> 
> On Sun, May 1, 2016 at 12:26 PM, Bill Baker via time-nuts <
> time-nuts at febo.com> wrote:
> 
>> My problem:  I'd like some kind of off-the-shelf device that can take the
>> time code and switch on or impulse another circuit-- specifically  I'd like
>> to trigger a 180 year-old fog bell (I'm a lighthouse nut as well,
>> www.henryisland.com) on the hour and maybe be able to impulse my minute
>> school clocks.  I'm not at this group's technical level, so it's got to be
>> pretty easy to program. So I need a box that I can program with SMPTE time
>> in and a timed switch impulse out.  Any ideas?
> 
> 
> I assume you only need to be accurate to within about 1/10th of a second or
> so.  Any general purpose computer like and old PC can do this but today
> you'd go with a Raspberry Pi 2 or some other single board computer.   The
> first step is to keep the computer's internal clock in sync with your time
> signal (NTP can do that and NTP will likely already be installed on the
> computer)  then if the computer is running a Unix-like OS (such as Linux,
> BSD or Mac OS X) there is a table you can set up that will run various apps
> at certain scheduled times.   You'd simply set s cron tab entry to blow the
> horn on every hour every hour.  

cron isn’t good enough for < 1s accuracy timing even with a GPS steered clock.
It only wakes up every minute and the time used scanning all crontab tables to see what needs to be run in that minute and scheduling those means that you rarely get a job executed in < 1s of the desired time.