[time-nuts] Sidereal timekeeping

shalimr9 at gmail.com shalimr9 at gmail.com
Wed May 18 20:17:59 UTC 2011


That's even simpler! You have to size the capacitor just right, but it's probably not too critical.
Thanks Chuck

Didier KO4BB

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

-----Original Message-----
From: Chuck Harris <cfharris at erols.com>
Sender: time-nuts-bounces at febo.com
Date: Wed, 18 May 2011 14:09:39 
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] Sidereal timekeeping

It's been a while since I did it, but as I recall, a simple way of
driving the typical motor on a dime store clock is:


FF-Q-------------)|-------------MOTOR--------+
.............................................|
FF-/Q----------------------------------------+

The capacitor charges up during the times when the FF's output is level,
and produces a spike of alternating polarity when the FF toggles.

You need 1 level transition every second, so the FF has to toggle at
a 1/2 HZ rate.

-Chuck Harris

David Martindale wrote:
> The motor is essentially a permanent-magnet stepper motor.  The rotor
> and stator have just 2 poles each, so the rotor has two stable
> positions 180 degrees apart that provide holding torque.  Thus, the
> motor holds position with no input current for most of each cycle.  To
> move it, the drive applies a short current pulse to the motor.  The
> pulses are alternating positive and negative polarity, so you'll need
> something like an H-bridge to drive it.  Using a 3 volt supply instead
> of the 1.5 that the motor was designed for would supply more power
> than the motor needs if you keep the drive pulse the same width, but
> you should be able to reduce the pulse width until the energy is about
> the same as with 1.5 V drive and have the motor still operate.
>
> Without having actually tried it, I think you should be able to select
> a suitable tradeoff between reliable motor operation and power
> consumption just by adjusting the "on" time of the drive pulse - no
> voltage regulator or voltage dropping resistor needed.
>
> There's only one stator coil to the motor, and one drive signal, so
> you can't control motor direction.  The magnetic structures are
> apparently deliberately asymmetric to ensure that the motor always
> rotates in one direction when it receives a pulse of the appropriate
> polarity.  (Get the pulse polarity wrong, and the motor just doesn't
> rotate).
>
>       Dave

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