[time-nuts] Driving clocks from 1pps

[Didier Juges]

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Tom Van Baak
> Sent: Thursday, September 04, 2008 6:37 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Driving clocks from 1pps
> 
> > 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.
> > 
> > 73,
> > Murray ZL1BPU
> 
> 50% duty cycle is way overkill, perhaps even harmful. In the 
> 'scope traces below you can see the IC generates just 50 ms 
> biphase pulses every second. That's 1/20, or 5% duty cycle.
> 
> http://www.leapsecond.com/pages/32kHz/
> 
> /tvb
> 

With the right size capacitor, you can get just the right amount of energy,
equivalent to the pulse you show on the scope.

The motor may need slightly more or less energy to account for the different
waveshape, but you should not end up very far.

Didier