Newsgroups: sci.electronics
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!batcomputer!cornell!uw-beaver!milton!serval!yoda.eecs.wsu.edu!ckinsman
From: ckinsman@yoda.eecs.wsu.edu (Chris Kinsman)
Subject: Re: IR receiver on traffic lights ?
Message-ID: <1991Apr12.232448.22646@serval.net.wsu.edu>
Sender: news@serval.net.wsu.edu (USENET News System)
Organization: Washington State University
References: <1991Apr12.042157.6685@engage.enet.dec.com> <1991Apr12.063837.7120@bradley.bradley.edu>
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Date: Fri, 12 Apr 91 23:24:48 GMT

In article <1991Apr12.063837.7120@bradley.bradley.edu> sony@buhub.bradley.edu (David Lennie) writes:
>In <1991Apr12.042157.6685@engage.enet.dec.com> moroney@ramblr.enet.dec.com writes:
>
>>Some systems have a photoelectric sensor aimed at the traffic lanes and a phase
>>locked loop circuit that is synchronized to the flashing emergency lights on
>>the emergency vehicles. When the PLL detects the flashing lights in a certain
>>direction, it turns the light green in that direction.
>
>Wouldn't this also detect the flashing lights on construction vehicles
>or tow trucks?
>
>Does the sensor simply pick up the presence of any flashing light or
>does it confirm that it is actually a police or fire vehicle by
>measuring frequency of flashes or something similar?  If it does
>measure the frequency, wouldn't it be susceptible to error due to
>slight variances in the flash frequency caused by low or high battery
>voltage in the vehicle?
>
>I am intrigued (obviously).  Explain furthur.

The ones I have seen detect a frequency range as well as pattern.  It is
usually not just the strobes in the light bar but a special strobe designed
for this purpose.  (This is an option on most new EVs.

Chris

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