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Date: Fri, 16 Mar 2012 14:26:53 -0400
From: Dave McGuire <mcguire AT neurotica DOT com>
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To: geda-user AT delorie DOT com
Subject: Re: [geda-user] Daughter's Science Fair
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On 03/16/2012 01:48 PM, Colin D Bennett wrote:
>> The magnetic field needs to be changing in order to induce a
>> current in the other coil.  You can do this in two ways:
>> 1) Use a AC power source instead of the DC battery
>
> Another variation would be to convert the dc power from the battery
> into pulsed dc.  If you have an Arduino or other microcontroller
> development tools, you could write a 5-line program to generate a
> pulsed logic output, and use that to control a MOSFET or BJT which
> switches the current to your first nail electromagnet.  Then the
> second electromagnet will have an induced voltage because the
> current through the first is frequently changing.
>
> The induced voltage in the second coil is proportional
> to the CHANGE in current of the first coil at any instant.
>
> You could even add a couple of potentiometers to the
> microcontroller circuit any allow poeple to vary the duty cycle and
> frequency of the pulsed output (pulse width modulation = PWM).

   Or, heck, use a 555 or a two-transistor multivibrator.

   Either way it'll be a fun project and great for the kids.  I love 
seeing stuff like this happen.

               -Dave

-- 
Dave McGuire, AK4HZ
New Kensington, PA