[time-nuts] Driving clocks from 1pps

[Lux, James P]

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Murray Greenman
Sent: Thursday, September 04, 2008 2:30 PM
To: time-nuts at febo.com
Subject: [time-nuts] Driving clocks from 1pps

In the light of the latest posts on driving clocks from 1pps, it sounds as though I'd better rethink what I was planning!

I am in the middle of the design of a micro which uses a 10MHz crystal to provide a digital clock, but the time is kept in line via GPS using a 1pps NCO, which is steered digitally, rather than altering the 10MHz oscillator in GPSDO fashion.

The plan was to provide two outputs (biphase) at 1pps to drive slave clocks, but in the light of the notes from Brooke and Chuck, I would be better off just providing a single output, and use a series cacacitor.

Chuck, I would expect that the 1pps would need to be about 50% duty cycle, or at least have a pulse width of 100ms or so. I can imagine a clock driven from 1pps with a low duty cycle would sound quite different.

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On the little clock I have here (a MFJ 24 hour clock, as it happens), the pulse going to the single coil is very short (a few ms?).  The armature appears to be spring loaded, so the core is normally outside the coil.  A pulse comes in, the core flies through, advancing the escapment mechanism.  The innards are all under a blob of epoxy, but I'd guess that it's something like a capacitor that gets discharged through the coil.

Jim