The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: email@example.com (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.firstname.lastname@example.org>...
> 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?
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup