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: "Don Cleveland"
Subject: Re: wire loop proximity alarm schematic
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Date: Fri, 29 Nov 2002 17:50:34 -0500
NNTP-Posting-Date: Fri, 29 Nov 2002 17:50:18 EST
Organization: WorldCom Canada Ltd. News Reader Service
Rene Tschaggelar wrote in message
> Smile, it can only get WORSE wrote:
> > Hi Everyone,
> > I'd like to build a large loop proximity alarm to detect humans
> > entering our yard. PIR motion detectors are impractical as it would
> > take too many of them to cover the area around our house. I know the
> > PIR is popular and cheap today, but I really want an old fashioned
> > simple proximity loop based alarm.
> > Years ago, they had wire loops strung at 8 to 10 feet above ground.
> > The loop was the inductor in a free running oscillator circuit.
> > Whenever a human (or critter) came near the loop, the resonant
> > frequency would shift due to the added stray capacitance...and the
> > loop would change frequency. The short term (rapid) change in
> > frequency was detected, and it set off the alarm.
> > My guess is that they would use a slow responding phase locked loop
> > and detect the time that it took for the loop to relock in order to
> > control the sensitivity.
> > I don't see these being used today and a web search seems to turn up
> > nothing.
> > Anyone have plans for these??? I'd like to have a battery powered
> > unit, but anything that runs is OK....the battery powered unit would
> > be for keeping smaller critters out of our garden.
> Why would such a loop detect humans ?
> Because they influence the field with the rifles and guns ?
> A low frequency wire has primarily a magnetic field that
> is influenced by magnetic conductors, such as iron. At a certain degree
> other conductors can be detected as they induce stray fields.
> You may not go much higher in frequency as when it really begins
> to radiate, the FCC will come to knok on your door.
> Then consider wind to change the configuration and produce false
> alarms. And finally, it will act as lightning protecting and be
> susceptible to wheather again.
> Ing.Buero R.Tschaggelar - http://www.ibrtses.com
> & commercial newsgroups - http://www.talkto.net
Look at www.bik.com
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup