Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!uwm.edu!bionet!agate!ucbvax!dog.ee.lbl.gov!nosc!crash!simpact!jeh From: jeh@dcs.simpact.com Newsgroups: sci.electronics Subject: Re: IR receiver on traffic lights ? Message-ID: <1991Apr15.120051.2273@dcs.simpact.com> Date: 15 Apr 91 19:00:51 GMT References: <1991Apr12.042157.6685@engage.enet.dec.com> <1991Apr12.063837.7120@bradley.bradley.edu> <31802@ucsd.Edu> Distribution: na Organization: Simpact Associates, San Diego CA Lines: 45 In article , khan@mrcnext.uiuc.edu (Scott Coleman) writes: > brian@ucsd.Edu (Brian Kantor) writes: > >>The "Opticon" sensors in use throughout San Diego County for traffic >>light control by emergency vehicles use a photocell in a focusing >>assembly that's pointed down the road. They ignore changes in ambient >>light levels and look for flash rates of either 10 or 16 hz, which the >>bus or emergency vehicle generates with a very bright xenon strobelight. > > Hmm... Sounds to me like a few parts from Radio Shaft will get you a sure- > fire way to minimize the dreaded morning commute! ;-) ^^^^ was this pun intentional?? A buddy of mine (in the LA area, where the same system is used) once decided to try this. The foundation for the project was a Sears automotive timing light with inductive pickup. This got him the strobe, housing, and a condensing lens. A normal timing light only fires when triggered by a signal from the #1 spark plug. He added a simple 555-based timer to do the triggering, a pot to adjust the frequency, and a switch, all mounted inside the timing light case. The power-lead clips, intended for attachment to the car battery terminals, were removed and replaced with a lighter-socket plug. The switch disconnected the 555 circuit and allowed the unit to be used for its originally-intended function. It turns out that the standard condensing lens in the timing light (intended for directing the strobe output onto a small area no more than a foot or so away) was nowhere near good enough to do the job. He experimented with various optics (C&H Sales in Pasadena, with its warehouse full of govt. surplus optics, being somewhat nearby) and actually got the thing to work, after a fashion. Trouble was, the aiming was very finicky, and the Opticon (Opticom?) pickup unit apparently needs to see the required flash-frequency for several seconds. He had envisioned being able to reach into the back seat, pull out this huge chrome-plated buck-rogers-raygun-looking THING, squeeze off a shot at the traffic light, and be done with it; reality was much less emotionally satisfying. He still uses the unit as a timing light, and just smiles when asked what that extra knob is for. --- Jamie Hanrahan (x1116), Simpact Associates, San Diego CA Internet: jeh@dcs.simpact.com, or if that fails, jeh@crash.cts.com Uucp: ...{crash,scubed,decwrl}!simpact!jeh