Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!bloom-beacon!mit-eddie!uw-beaver!fluke!strong
From: strong@tc.fluke.COM (Norm Strong)
Newsgroups: sci.electronics
Subject: Re: Car Detectors for Traffic Lights
Message-ID: <8705@fluke.COM>
Date: 31 May 89 18:51:33 GMT
References: <18811@cup.portal.com> <3185@kitty.UUCP> <456@antares.UUCP>
Sender: news@tc.fluke.COM
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 27

In article <456@antares.UUCP> pnelson@antares.UUCP (Phil Nelson) writes:
}In article <3185@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:
}>In article <18811@cup.portal.com>, mmm@cup.portal.com (Mark Robert Thorson) writes:
}>> Does anybody know how the car detectors for traffic lights work?  Are
}>> they tuned circuits?  If so, what frequency?
}
}
}>> More importantly, can they be activated from a distance?
}>
}>	On the assumption that a magnetic disturbance detector is involved,
}>the answer is most likely no.  If memory serves me correctly, the Eagle
}>Signal unit that I have uses a coincidence circuit which requires detected
}>signals to be in-phase with the excitation oscillator, thereby minimizing
}>the probability of external interference.
}
} I have a related question, can they be activated without the metal mass?
}The question has probably been asked before, it must be a common problem
}for urban bicyclists; how do you get the left-turn light to change? I
}havn't seen any solution though, is everyone waiting for George to do it?

There's one of these space age traffic lights at the corner where everyone
runs at lunchtime.  It will go through its cycle with or without masses of
metal; it just takes longer.  (Probably longer than you care to wait.)

-- 

Norm   (strong@tc.fluke.com)