mmm@cup.portal.com (Mark Robert Thorson) (05/26/89)
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?
larry@kitty.UUCP (Larry Lippman) (05/28/89)
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? The very first vehicle detectors were treadle switches that were recessed into the pavement. Needless to say, the constant mechanical stress and effects of weather did not contribute to the reliability of such detectors. During the 1950's when electronic car detectors first saw widespread use, the detection methods were primarily ultrasonic and microwave. Various reliability problems with such detector methodology have resulted in the the magnetic disturbance detector being the favored mode of detection. Magnetic disturbance detectors operate through a buried loop of wire. There are various schemes in use, some of which use two coils, and others use a single coil. The simplest technique involves a single coil inserted as one arm of an inductance bridge, with the vehicle metal mass cauing an increase in inductance. A more reliable technique uses two coils, with the vehicle metal mass causing a change in permiability of the "air" core. Since both of these magnetic techniques require AC excitation and since the coils are large, the excitation frequencies in use range between 50 and 150 kHz. I have an older (mid 1970's vintage) Eagle Signal unit in my driveway as an announciator, and it runs around 75 kHz. I have also seen a Hall effect sensor for vehicle indication which requires only a single point for burial in the roadway, as opposed to cutting a 360 degree loop in the pavement. > 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 won't even begin to ponder why you pose this question. :-) <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {att|hplabs|utzoo}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"
pnelson@antares.UUCP (Phil Nelson) (05/29/89)
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 won't even begin to ponder why you pose this question. :-) > 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? So, what kind of transmitter do I need to trip these things? Could it be carried on a bicycle? The phase problem seems easy enough, simply build a receiver-transmitter combination that retransmits in phase with received signals. I wonder how much power I need though, if I have to pack 20lbs of electronics and a 10' diameter antenna on my bike, it won't be worth it. Also if I have to have a separate system for each style of detector things could get complicated. Anyone tried anything like this? There might even be some money in it, if the price of helmets is any indication. I can't believe I just paid $75. for 7 oz. of Styrofoam. ><> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. ><> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry -- Phil Nelson at (but not speaking for) OnTyme:NSC.P/Nelson Tymnet, McDonnell Douglas Network Systems Company Voice:408-922-7508 UUCP:{pyramid|ames}oliveb!tymix!pnelson LRV:Component Station "ding ding..." -Santa Clara County Transit Company trolley car (AKA "LRV")
todd@ivucsb.sba.ca.us (Todd Day) (05/30/89)
In article <456@antares.uucp> pnelson@antares.UUCP (Phil Nelson) writes:
~ 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?
Well, these things must have sensitivity adjustments, because there is
a set of them on the UCSB campus that controls a bike/car intersection.
Bikes have no trouble setting off the loops on the bikepath. The cuts
in the pavement make me think that the mechanism is no different than
that used for cars at "real" intersections.
--
Todd Day | todd@ivucsb.sba.ca.us | ivucsb!todd@anise.acc.com
"All theory, no practice. That's the story of my life."subelman@ttidca.TTI.COM (Ed Subelman) (05/30/89)
In article <456@antares.UUCP> pnelson@antares.UUCP (Phil Nelson) writes: >Subject: Re: Car Detectors for Traffic Lights >Summary: How can I trigger them from my bicycle? In my younger days as a bicycle rider I found that I could usually trigger the car detectors for traffic lights by riding my bicycle so that the wheels ran exactly over, and in the same direction as, the cuts in the pavement where the wires for the car detector loop were buried. I would usually stop to wait for the light to change with both wheels sitting on this cut. I have not tried this in 10 years, so your mileage may vary. -- Ed Subelman subelman@ttidca.TTI.COM Citicorp(+)TTI {csun|philabs|psivax}!ttidca!subelman 3100 Ocean Park Blvd. Santa Monica, CA 90405 (213) 452-9191, x2972
bill@sigma.UUCP (William Swan) (05/31/89)
In article <806@ivucsb.sba.ca.us> ivucsb!todd@anise.acc.com (Todd Day) writes: }~ 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? } }Well, these things must have sensitivity adjustments, because there is }a set of them on the UCSB campus that controls a bike/car intersection. }Bikes have no trouble setting off the loops on the bikepath. The cuts }in the pavement make me think that the mechanism is no different than }that used for cars at "real" intersections. But UCSB/Isla Vista is hardly the world at large. Ten years ago (the last I could speak for the place), it was *very* heavy in bike riders, and rather low in auto traffic (most of the time). A special, more sensitive detector would make a lot of sense there. Most places there are a lot fewer bikes around, and the sensitivity of the detectors, whether inherent or setpoint, is a lot lower. To ride out of my business park, I have to get over to the pedestrian button (on the *left* side of the intersection as I leave) to get the signal to change. Now, me, *I've* been thinking about those optical sensors used by emergency vehicles :-) :-) (Check your local regs first - likely to be quite illegal - not to mention dangerous if a *real* emergency vehicle is headed towards the light!! Not to mention your legal liabilities in latter case...) -- William Swan grace.apl.washington.edu!sigma!bill Send USmail addr for info: Innocent but in prison in Washington State for 13.5 years: Ms. Debbie Runyan: incarcerated 01/1989, scheduled release 07/2002. In now: 0 years, 4 months, 1 week, 3 days.
Brad_Tiger_Houser@cup.portal.com (05/31/89)
While we are on the subject, in various Silicon Valley intersections there are what appear to be Microwave antennas on the overhead signals. A friend told me they were for picking up transmissions from the public transit buses. It looks like the bus has something that looks like a 4" outdoor speaker on top. Are the buses able to tell the street lights something like "Don't turn red yet, I am coming through" or "Turn green in 30 seconds"? If so, anyone out there know the secret to this? Frequencies? Codes? (Legalities if caught using one?) Brad Houser Intel Corporation Typical disclaimer deleted
jim@ghp.UUCP (Jim Stewart) (05/31/89)
In article <18811@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? From university days...we used to open the exit gates in the parking lots with the right sized closed loop of wire. It would obviously detune the car detector and open the gate. In case you are wondering, it started out as a practical joke on the old lady who was the cashier for one of the lots. People would ride their bicycles past the in-gate and a ticket would come out. Of course the machine would buzz until she got annoyed and came out of her kiosk to remove the ticket. The poor dear must have had to put down her knitting at least 5 times a morning for this, and in the winter it was cold outside. (University of Waterloo '79) We tried to do the same thing with a loop of wire in your shoe, but found we needed a loop diameter of about 2 feet even if we used multiple turns. -- Jim Stewart, VE3SRJ UUCP: jim%ghp@mnetor.uucp BELL: (416)862-0430
rjd@occrsh.ATT.COM (Randy_Davis) (06/01/89)
In article <456@antares.UUCP| pnelson@antares.UUCP (Phil Nelson) writes: | 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? Though I would be interested in the "trigger from a distance" answer, Phil's bicycle question is going to be of great interest to motorcyclists also, especially those who ride small bikes. Plus, motorcycles would already have a power source on board.... Though I ride a fairly large bike (650 pound with a steel frame), there are *still* some lights that will ignore me. This can be a real pain if there are no cars approaching from behind to trigger the light for you, thus making me have to run lights after sitting at them for long periods. (Other methods exist, like trying to remember which ones ignore you, or going through the handy service station [which isn't legal either], etc... but this gadget would be nice.) So, if anyone knows a way to fool a light into thinking there is a larger metal mass above the sensor than there actually is, please post!!! Randy Davis UUCP: ...(att!)ocrjd!randy ...(att!)occrsh!rjd
strong@tc.fluke.COM (Norm Strong) (06/01/89)
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)
brian@ucsd.EDU (Brian Kantor) (06/01/89)
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
larry@kitty.UUCP (Larry Lippman) (06/02/89)
In article <1741@ucsd.EDU>, brian@ucsd.EDU (Brian Kantor) writes: > 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. Gee, it's too bad they don't have those kind of traffic lights in the area of NY State where I live; I could have some fun. :-) I wonder if the traffic light optical sensors are sensitive to IR, and would trip from some pulsed IR energy from a high-power diode array? This would certainly result in a rather unobtrusive, ahem, "automotive accessory". I tend to feel that any optical sensor of this nature would respond to some really _decent_ IR energy, as emitted from an injection laser diode. However, a laser diode does present some safety concerns, in addition to a directivity problem due to lack of beam dispersion. <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"
erk@americ.UUCP (Erick Parsons) (06/03/89)
><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? Ill give this one a try though it's been a few years since I've actually read any literature on vehicle detectors. I may be wrong on some points but overall it is sound. Basically you will have two type of vehicle detectors in any *Modern* traffic actuated signal system. There are magnetometer detectors and loop detectors. The magnetometer detectors are very straightforward in operation and theory and are likened to proximity sensors used in industrial control systems. It is a high current device and therefore low impedance making High power a necessity to induce into it. A costly, bulky and possibly futile project. These are being phased out in my county (Sacramento) and being replaced with: Loop detectors, or Induction detectors are a reletively new type of sensor (as compared to magnetometer det's) and work on the principle of changing the resonance of a tuned coil of wire in the street so as to cause a small frequency shift at the sensing device in the controller cabinet. The loops are buried in about 3-4 inches of asphalt and connect directly to the detector (electronic device that senses the inductance change). There is not a whole lot of wire to induce into and coupled with the fact that asphalt makes a Da*n good ground a radio transmission would appear futile for tripping one of these beasties. (Our local Elec. Co. SMUD sometimes uses the roads for ground conn's to their system by sawcutting the asphalt and laying their bare ground wire in the sawcut covering it and running it to their ground point on the power pole). The detector connected to the loops also has some built in features (uP cntrl) that will try to avoid any bogus vehicle calls being sent to the controller equipment. An average detector will have such features as automatic cancellation of a gradual buildup in conductive material placed in close proximity to the loop i.e. rain, snow, garbage muffler parts whatever, that appear to be smaller than a bicycle. Larger pieces that could cause the detector to think that a vehicle is parked on the sensor will be cancelled out after a fairly long wait, I would guess about 10 minutes. As to your question what frequency do they run at, there is no set frequency, the loops cannot possibly be made exactly the same any two times and coupled with the fact that there will probably be 4 to 8 loops on one channel the error multiplies. On the other end the detectors are constantly adjusting for frequency drifts, have 3 frequency settings and 10 sensetivity levels. I wouldn't bother trying as you will in all likelyhood pull your hair out ITP, In the event that you do find a way to mount a 500KW transmitter on your car (truck, big rig) and do manage to trip the sensors through some sort of wizardry you will in all likelyhood trip all of the other sensors and cause the I/S to cycle through before serving you, probably locking up the system completely for the ~10 minutes it takes to cancel junk on the loops and pissing off the City, County, State personnel that maintain and repair these buggers. Relax: Don't hurry be wappy :-) And remember to give those boys (and girls) a brake. -- ------------------ // -----------Cut-Here---------------------------------- Erick Parsons // Words for the wise: *If it works don't fix it.* Sacramento Ca // mail to: ...pacbell!sactoh0!americ!erk ------------- \\// --------------------------------------------------------
keithl@loop.UUCP (Keith Lofstrom) (06/05/89)
>}~for urban bicyclists; how do you get the left-turn light to change?
The sensors are usually inductive - I have had 90% success in laying my
bicycle down sideways so the center triangle is over the diamond shaped
loop in the street. Some sensors aren't sensitive enough, though, and
it's hard to do with a loaded bike.
I can imagine a gadget that could spoof such a sensor, perhaps even from
a short distance - wouldn't it be nice to trip the sensor 10 seconds before
you get there? Oh well, I'm usually riding the bike to GET AWAY from
electronics!
--
Keith Lofstrom keithl@loop tektronix!tessi!qiclab!loop!keithl
Launch Loop, P.O. Box 1538, Portland, Oregon 97207 (503)-628-3645pvo@uther.CS.ORST.EDU (Paul V O'Neill) (06/07/89)
In article <722@occrsh.ATT.COM> rjd@occrsh.UUCP (Randy_Davis) writes: > > So, if anyone knows a way to fool a light into thinking there is a larger >metal mass above the sensor than there actually is, please post!!! > >Randy Davis UUCP: ...(att!)ocrjd!randy > ...(att!)occrsh!rjd Here are 2 methods that work for me on a small motorcycle. 1) High speed crossing of the coil followed by *hard* braking. (directly over asphalt cut of a long & rectangular sensor) (down the middle of a diamond shaped detector) [Careful here -- you won't have maximum braking power available because of the oil and grime that accumulates at the intersection.] 2) If 1) fails.... put the side stand down on top of the asphalt cut. Paul O'Neill pvo@oce.orst.edu Coastal Imaging Lab OSU--Oceanography Corvallis, OR 97331 503-754-3251
nagle@well.UUCP (John Nagle) (06/07/89)
Recent developments in traffic detectors include ones sensitive enough
to detect bicycles. These are indicated by a white box outlining the detector
loop in the pavement. Proper use is to ride the bicycle over the edge of the
box, not through the center. Many unmarked detectors will respond to bicycles
if you locate the loop and align the bicycle wheel with the edge. In stubborn
cases, laying the bike flat over the loop will usually trip it.
Some recent work involves using signal processing equipment to
distinguish cars, trucks, and buses from the loop signal alone. First
use of this technology was in Germany.
John Nagle