[time-nuts] Driving clocks from 1pps
Bill Beam
wbeam at gci.net
Fri Sep 5 02:38:55 EDT 2008
On Thu, 04 Sep 2008 21:16:43 -0700, Tom Van Baak wrote:
>>> 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.
>>
>> No Tom, you misunderstand. The 50% duty cycle pulse provides the
>> rising and falling edges. The small capacitor differentiates
>> that to produce a positive going, or a negative going pulse to
>> make the motor move.
>>
>> -Chuck Harris
>
>Ah, I see now. It's a 0.5 Hz square wave. Cool. Yes, that looks
>like it might work. Has someone tried this on a quartz clock
>stepper motor to make sure you reliably get sufficient impulse?
>I wonder why no commercial clocks use this trick.
>
>/tvb
>
It works perfectly and reliably. I drive three wall clocks from the
0.5Hz heartbeat of a Brooks Shera controller with 50-100microF
in series to each clock. You need a way to reverse polarity to
get onto even or odd second. Five $ wall clocks keeping GPS
accurate time.
>
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Bill Beam
NL7F
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