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Date:	Fri, 16 Mar 2012 10:48:35 -0700
From:	Colin D Bennett <colin AT gibibit DOT com>
To:	geda-user AT delorie DOT com
Subject:	Re: [geda-user] Daughter's Science Fair
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On Fri, 16 Mar 2012 12:59:21 -0400
John Hudak <jjhudak AT gmail DOT com> 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).

Regards,
Colin

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