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From: tomb@hplsla.HP.COM (Tom Bruhns)
Newsgroups: sci.electronics
Subject: Re: Making a clodk go at twice the normal speed.
Message-ID: <5170087@hplsla.HP.COM>
Date: 24 Aug 90 15:59:16 GMT
References: <1990Aug23.173721.7942@arnor.uucp>
Organization: HP Lake Stevens, WA
Lines: 38

>Is it possible to change the gearing or the crystal frequency in a
>simple manner.  I am willing to buy a clock in kit form, if these are
>available,  and then put a divider in the circuit which can be
>switched on and off by a switch.  I think gears are an inelegant
>solution.  
This may work, but (1) it may be tough to locate a suitable crystal
and (2) the divider chip may really be optimized for a particular
frequency.  Anyway, as cheap as these things are, it would be worth
a try.  JAN Crystals in Ft. Meyers FL may be able to help with a
crystal.  Most common ones are 32768 Hz, I believe, so you'd want
65532.  You might be able to build a simple oscillator and divider
chain to get 65532 from, say, 16 times that, and then divide it
down further to get the standard and half-rate clocks, too.

>The other things I though of was to get a wall clock that operates on
>50 Hz, 110 v and somehow double the frequency of the current.  Would
 ^^ Looks like you are in the US.  Sure you don't mean 60 Hz?
>this work?

>Is there a simple way to double the frequency of the Ac going into the
>clock.  The two ways I could think of doing this were 
>1. Have a motor pair, and vary the speed of the motor and hence the
>frequency of the current generated by the AC generator.
You could make this continuously variable, a possible advantage.  Beware
of trying to operate the motor at too low a frequency; it will draw
excessive current unless you limit the voltage, and with limited
voltage may possibly not have enough torque to turn the clock hands.

>2. Use an SCR to chop up the incoming sinewave so as to double the
>frequency.  Will this work?
Much easier to just full-wave rectify the line and put a capacitor in
series to filter out the DC.  You will have to put a DC return path in
for the rectifier, or you will just charge up the cap and it won't pass
any significant current.  

You could also use a little amplifier--most clocks are 5 watts or less.
Use a simple transformer to step the voltage back up.  Find an audio
oscillator to drive the amplifier (or use a computer audio output...)