[time-nuts] 50/60 Hz clocks

shalimr9 at gmail.com shalimr9 at gmail.com
Sun Mar 20 21:31:02 UTC 2011


If the plan is to drive a mechanical clock, I assume long term stability is more important than phase noise. Many small microcontrollers (I use 8051's from Silabs) have a built-in PLL that can be set to run at 15 MHz from an external 10 MHz reference (applied to the external oscillator input), and use the program space to implement a divider that will give you exactly 60 Hz. That is a one chip solution. The processor will accept the sinewave from the reference oscillator without extra shaping circuit. 

Didier KO4BB

Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Sender: time-nuts-bounces at febo.com
Date: Sun, 20 Mar 2011 09:30:03 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] 50/60 Hz clocks

An OTT solution might employ a regenerative divider to generate a 15MHz 
signal from a 10MHz input followed by a digital divide by 250,000 circuit.
One could employ an inexpensive Gilbert cell mixer in the regenerative 
divider to keep the cost down.

Bruce

Bob Camp wrote:
> Hi
>
> Most likely the lowest parts count is to divide to a narrow(ish) 20 Hz square wave and then drive a resonated transformer with a pulse. The output won't look pretty, but it should drive a small clock motor just fine. Done properly, there should be very little power involved.
>
> If you are going to use anything complicated, just run a gizmo that lets you have a PLL at a factor of 3 times the input. Once that's done - problem solved.
>
> Bob
>
> On Mar 19, 2011, at 3:01 PM, Michael Poulos wrote:
>
>    
>> Robert LaJeunesse wrote:
>>      
>>> Poor man's solution: Use an Arduino to read the Thunderbolt 1PPS and lock a 50Hz (or 60Hz) square wave to the 1PPS. Any resulting jitter can likely be kept in the tens of microsecond range, easily filtered out by the clock mechanics. Filter the square wave a bit and feed it into an audio amplifier (or two) of sufficient power to run the clock. (Possibly a 12V powered bridge amplifier at ~14W would be adequate?)  Use some sort of audio output or filament transformer backwards to create the proper line voltage to run the clock. Maybe run the whole thing off a 12V battery with float charger for uninterruptible timing.
>>>        
>> When using the power transformer "backwards" keep in mind the impedance output of the amplifier. Audio amplifiers are rated in watts into an 8 ohm (or 4 ohm) load. So, what you want is a power transformer of desired wattage and the low voltage side having a volt and amps rating that would match an 8 ohm load or 4 ohm load. Then, you hook it "backwards" (i.e. as a step-up transformer) to an audio amp of a rating higher than the transformer then hook the signal to the input and use the volume knob as a throttle. Turn up until desired voltage is reached.
>>
>> Have fun!
>>
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