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From: sony@buhub.bradley.edu (David Lennie)
Newsgroups: sci.electronics
Subject: Re: IR receiver on traffic lights ?
Message-ID: <1991Apr12.063837.7120@bradley.bradley.edu>
Date: 12 Apr 91 06:38:37 GMT
References: <1991Apr12.042157.6685@engage.enet.dec.com>
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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.