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From: firstname.lastname@example.org (Sara Berg)
Subject: Re: passive circuit excitation
Date: 4 Jan 2003 15:33:58 -0800
NNTP-Posting-Date: 4 Jan 2003 23:33:58 GMT
Joe Legris wrote in message news:<3E171373.email@example.com>...
> Sara Berg wrote:
> > hi there group :),
> > can anyone tell me whether it is possible to excite a passive
> > (dormant)circuit into active operation simply by exposing it to a
> > certain radio frequency? let's say that my telephone's ringing signal
> > is XY KHz and i want to place next to it a bulb with a circuit that
> > will close only when the phone rings (ie. when the circuit is exposed
> > to this XY frequency) thus allowing power to go through it and light
> > the bulb.
> > does the signal level (amplitude) have any meaning in such a scenario?
> > Thanks a lot,
> > Sara.
> Amplitude is everything because a passive circuit will have to get all
> its energy from the sound wave, which, unless your phone is as loud as a
> fog horn, will be insufficient to light a lamp. You will need an
> additional source of power.
> Radio Shack sells such a device - it plugs into the phone line.
> If you cannot attach to the phone line then it is practical to use a
> small battery powered circuit containing a microphone, amplifier, filter
> and switch for the lamp. In its "dormant" state the battery should last
> for months.
> Best regards,
> Joe Legris
Joe, thanks! but in this scenario, how can i differentiate between the
sound of the phone and other loud sounds? and what if i want to do it
without a mic - isnt there anything that can respond to a specific
frequency (not a sound wave necessarily), perhaps a transponder?
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