murthy@arnor.watson.ibm.com (Sesh Murthy) (08/24/90)
A friend of mine would like to change the speed up a clock by a factor of 2.0 or 0.5 for a psychology experiment. I was wondering if there is any simple way to do this. I know that the commercially avialable battery driven clocks use a crystal, bring down the frequency using a divider and then drive a stepper motor. This then drives some gears that drive the minute and second hands. I figured that changing the voltage would not help in this case. 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. 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 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. 2. Use an SCR to chop up the incoming sinewave so as to double the frequency. Will this work? If someone can tell me of a simpler way of doing things, or a simple way to implement any of these ideas, I would be grateful. Thanks Sesh Murthy
francis@hydracs.ua.oz.au (Francis Vaughan) (08/24/90)
In article <1990Aug23.173721.7942@arnor.uucp>, murthy@arnor.watson.ibm.com (Sesh Murthy) writes: |> A friend of mine would like to change the speed up a clock by a factor |> of 2.0 or 0.5 for a psychology experiment. |> |> I was wondering if there is any simple way to do this. |> A nasty thought comes to mind. Clocks as a rule run on the proverbial "smell of an oily rag" so this should work. Get a signal generator, a small lab audio amplifier and a power transformer. Run the transformer backwards from the amp which is fed with a nice sine wave from the signal generator. Need a bit of care in setting up to get the volts OK, but you also get infinitly variable time. Use an oversized transformer, so you don't saturate it on low frequencies. Francis Vaughan.
fmgst@unix.cis.pitt.edu (Filip Gieszczykiewicz) (08/24/90)
Greetings. I needed a clock to go 2 X the normal speed. Quite simple. Typical "Quartz" clock consists of: 1) p.c. boards with a resistor, crystal, IC, variable cap (minor adjustment), and 1 or 2 diodes (battery polarity protection). 2) coil that drives a small magnetic wheel (2 pole motor?) 3) Various gears to "derive" the minutes and hours. All I did was take a NE555 (timer chip) and set it to pulse 2 times per second. I connected the output of the 555 to a transistor that drove the coil. It work's just fine. (you can set the speed to anything!) Take care. P.S. Now, getting the clock to go BACKWARDS is an "adventure" (with a quartz, anyways.... :-) -- _______________________________________________________________________________ "The Force will be with you, always." It _is_ with me and has been for 10 years Filip Gieszczykiewicz "A man without a dream is like a fish without water." FMGST@PITTVMS or fmgst@unix.cis.pitt.edu "My ideas. ALL MINE!!"
tomb@hplsla.HP.COM (Tom Bruhns) (08/24/90)
>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...)
bill@videovax.tv.tek.com (William K. McFadden) (08/24/90)
The easiest way to do this is to run a variable sinewave oscillator (e.g.,
audio gernerator) into an audio power amplifier. Connect a standard AC wall
clock to the amplifier's output. With the frequency set to 60 Hz, gradually
increase the amplitude until the clock seems to be running normally (or use a
voltmeter to set the voltage to 120 VAC). To change the speed of the clock,
vary the frequency.
You will need to use a PA amplifier with a 70V output, since the 8 ohm outputs
on regular amplifiers don't put out enough voltage. If all you have is an 8
ohm amplifier, you can get a transformer from Radio Shack for about $5 that
adapts the 8 ohm output to 70 volts.
BTW, I have heard stories of coworkers doing this to chronic clock watchers.
They would set the clock to run slightly fast or slightly slow, being sure to
vary it a little every day. Drives 'em nuts!
--
Bill McFadden Tektronix, Inc. P.O. Box 500 MS 58-639 Beaverton, OR 97077
bill@videovax.tv.tek.com, {hplabs,uw-beaver,decvax}!tektronix!videovax!bill
Phone: (503) 627-6920 "The biggest difference between developing a missle
component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI