[time-nuts] Regulating a pendulum clock

Don Latham djl at montana.com
Mon Aug 9 05:05:44 UTC 2010


Oh, well, I have some 15 v baxck-to-back zeners extremely fast to help the 
fuse out. In any case, the max current is limited by the power supply 
Something can be worked out...
12 v actually limits the current through the coil(s) and heating even at 
full  on will not destroy anything. I'd probably use igbt transistors, I've 
become quite fond of them :-) Note that the design will not deliver any 
current through the coil if both gizzie outputs are either positive or 
negative.
I'll bet there's a small half-bridge or full h-bridge that will work 
extremely well, say sparkfun or the like. On fact, that's probably the best 
way to go; as the h-bridges are designed to drive inductive loads. Neat, I'm 
glad you kept my mind on task. A simple small motor driver will do the trick 
nicely.
Doe to age, my current philosophy is <buy the biggest piece you can>
Don

----- Original Message ----- 
From: "Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Sunday, August 08, 2010 5:22 PM
Subject: Re: [time-nuts] Regulating a pendulum clock


> Mere fast blow fuses aren't usually precise enough to protect transistors 
> against over current unless one uses rather large transistors.
> Overcurrent protected drivers are available and readily designed/built.
> Protection against di/dt transients due to external events is also 
> advisable.
>
> Minimising the parts count isn't necessarily conducive to improved 
> reliability when external hazards aren't taken into account.
>
> Merely resonating the coil without other filtering doesnt necessarily lead 
> to low EMI when driving it with a voltage waveform having high edge slew 
> rates.
> Some edge filtering to control the current flowing in the load capacitance 
> is also advisable.
>
> Bruce
>
>
> Don Latham wrote:
>> fast blow fuse, resonate the coil to the pwm frequency. Parts count 
>> small,
>> tinkering in software instead of breathing lead fumes or whatever noxious
>> stuff the Europeans have forced us to use...
>> Don
>>
>> Bruce Griffiths
>>
>>> No protection against external shorts or other undesired events.
>>> Extensive analog filtering to avoid creating an effective radiator of
>>> noise may also be necessary.
>>> Simple analog techniques are probably simpler/cheaper once the necessary
>>> filtering and protection are included.
>>>
>>> Bruce
>>>
>>> Don Latham wrote:
>>>
>>>> Hmmm lemme see. I think I'd use a 12 volt supply and two transistors
>>>> driven by two outputs on my Arduino,basic stamp,picaxe or other 
>>>> whizzie.
>>>> I'd then implement a PID controller essentially using the 1 sec pulse
>>>> from
>>>> the pendulum and the 1 sec pulse from my Rb, satellite receiver, 
>>>> crystal
>>>> clock, or whatever. The appropriate output pin will be brought to
>>>> ground,
>>>> and the other driven as a pdf with the rate given by the pid loop.
>>>> Temperature and even pressure corrections can be applied within the
>>>> gizzie
>>>> software. External parts, minimum. Opportunity to play with tuning,
>>>> maximum.
>>>> Don
>>>>
>>>> Bruce Griffiths
>>>>
>>>>
>>>>> J. Forster wrote:
>>>>>
>>>>>
>>>>>> You are picking very unimportant nits.
>>>>>>
>>>>>> If there were a small noise spike from the opamp, it'd goose the
>>>>>> pendulum
>>>>>> a tiny amount. That would be corrected on the next swing.
>>>>>>
>>>>>>
>>>>>>
>>>>> Heuristic analysis of this type is counter productive.
>>>>>
>>>>>
>>>>>
>>>>>> You are turning a trip to the corner store into an Apollo Moon
>>>>>> Mission.
>>>>>>
>>>>>>
>>>>>>
>>>>> Reliability is paramount in a circuit that may be required to work for
>>>>> decades.
>>>>>
>>>>>
>>>>>
>>>>>> BTW, since the =drive does not to be bipolar, one of the NPN and PNP
>>>>>> transistors can be deleted. They never turn on. So you are left with
>>>>>> two
>>>>>> opamsa, =each with a simple emitter follower.
>>>>>>
>>>>>>
>>>>>>
>>>>> The original request was for a bipolar drive.
>>>>> The lack of short circuit protection is poor design practice when
>>>>> driving an external load.
>>>>>
>>>>>
>>>>>
>>>>>> -John
>>>>>>
>>>>>> ==============
>>>>>>
>>>>>>
>>>>>>
>>>>> Bruce
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
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>>
>>
>
>
>
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