Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!pasteur!helios.ee.lbl.gov!ucsd!brian
From: brian@ucsd.EDU (Brian Kantor)
Newsgroups: sci.electronics
Subject: Re: Car Detectors for Traffic Lights
Message-ID: <1741@ucsd.EDU>
Date: 1 Jun 89 05:36:37 GMT
References: <18811@cup.portal.com> <3185@kitty.uucp> <456@antares.uucp> <806@ivucsb.sba.ca.us> <2388@sigma.UUCP>
Reply-To: brian@ucsd.edu (Brian Kantor)
Organization: The Avant-Garde of the Now, Ltd.
Lines: 16

About 10-15 years ago I modified one of those "electronic" automotive
timing lights (a Sears, I think) by replacing the trigger circuit
with a unijunction transistor oscillator driving a speaker transformer
wired in reverse.  It tripped the Opticon(?) sensors on the traffic
lights just fine after dark - it was too dim to work during the day.

As I recall, there were two frequencies sensed by the traffic light
controller - one would simply extend the green and was for use by
transit buses and such to save on gas and brakes, and the other
caused immediate green in one direction and red elseways.  I don't
remember the exact frequencies but they were slower than 20Hz, as
I recall.

I'm told that's now illegal: "tampering" with a traffic signal.
There's entirely too much law these days.
	- Brian