From: Joe Legris
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Subject: Re: passive circuit excitation
Date: Mon, 06 Jan 2003 11:31:45 -0500
NNTP-Posting-Date: Mon, 06 Jan 2003 11:30:44 EST
Organization: Bell Sympatico
Sara Berg wrote:
> 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
>>>does the signal level (amplitude) have any meaning in such a scenario?
>>>Thanks a lot,
>>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
> 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?
Sorry, I misread your original post and thought you were trying to
capture a sound wave.
You can do this electromagnetically but it may be tricky, depending on
your requirements. You don't have to worry about other SOUNDS, but you
may get interference from other electrical devices.
Why can't you just plug into the phone line?