Newsgroups: alt.horology,rec.arts.theatre.stagecraft
Subject: Re: Strange clock wanted
References: <[email protected]>
	<[email protected]>
From: Tomi Holger Engdahl 
Date: 03 Jun 1999 11:49:03 +0300
Message-ID: 
Organization: Helsinki University of Technology, Finland
Lines: 45
X-Newsreader: Gnus v5.3/Emacs 19.34
Ben Mehlman  writes:
> Robert Brown wrote:
> > To all lovers of strange clocks:
> >
> > I'm involved in a theatrical production that needs a 12" or so diameter
> > clock with hour and minute hands and no second hand. The clock needs to
> > so that I could make the clock
> > run at 50% or 100% or whatever percentage I choose. The clock could run
> > on AC or DC. Is there an easy method to accomplish this? Please email me
> 
> Yes, relatively easy.  You can make a regular AC wall clock run fast by
> driving it at a higher line frequency, eg for a US (60 Hz) clock, running it
> with  90 Hz AC will cause it to go 50% fast.  The only problem being that the
> clock motor is designed for 60 Hz so there are limits to how far any
> particular clock will be able to go.  You'll have to experiment.  As far as
> how to get the 90 Hz power, the easiest way is to use an audio signal
> generator (they are used in electronics labs, service shops, by audio
> engineers etc) to drive a decent sized amplifier.  The output of the amp goes
> to the low voltage side of a small power transformer, 120V -> 12V or 24V.
> The 120V side goes to the clock. 

That's a working idea. I have used a signal generator, amplifier
and transformer when I have needed AC voltages at strange frequencies.
For example I have used this method for generating telephone rign signals
at different frequencies and voltages for some telecomunication equipment
testing. If you have those tools then this might be one good alternative.
And then be careful with the wiring on that 120V or 230V AC side
(whatever line voltage you use).

Another idea:

Use the mechanics and electronics from a normal wall clock which
operates from 1.5V battery. Those have typically one IC, one 
crystal and one small electric motor in them. This electric motor
will work on the voltage the IC sends to it. Typically the
motor makes steps once or few times a second (you will hear
the typical very quiet click noise from clock).
If you take out the electronics and start feeding a square wave 
of 1-2V at around 1 Hz frequency to that motor, it will typically
start to move nicely. By adjusting the frequency you can adjust
the clock speed. You will have to do some experimenting, but this
has worked for me in some experiments.

-- 
Tomi Engdahl (http://www.iki.fi/then/)