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Lefty
HOW TO – Fool a stoplight into thinking your bike is a car – The Loop Sensor Activator via Core77.

A common problem for bicyclists, and in particular for bicycle commuters, is the traffic loop sensor. These are the devices which detect the presence of vehicles to control the sequencing of traffic lights at many intersections. Often, they are installed in figure-eight slits cut into the pavement near a traffic light.

The way they work is to detect the slight change in inductance of the loop of wire buried in the slit caused by a large metallic object (such as a motor vehicle) above the loop. The problem for bicyclists is that traffic departments often feel compelled to set the sensitivity of the electronics behind the loop rather low, so that false detections are avoided. This can make it difficult for a bicycle (a relatively small metal object) to make its presence known to the sequencing circuit. The result is a lot of frustration for a bicyclist trying to get a green light or left-turn arrow. This can be especially frustrating at streets with low traffic (often where these sensors are used in the first place), as one waits for a motor vehicle to come by and trip the sensor. Sometimes one must resort to laying the bicycle down on the road surface above the loop with the hope that the extra metal presented to the loop will cause detection. Sometimes it doesn’t work, and sometimes frames aren’t made of metal.

Various devices have been patented in order to address this problem. Some are a little impractical, and some don’t work with modern loop sensor circuitry. One patented solution (see USP 5,652,577) has the bicyclist laying down a big piece of metallic foil or screen right on the road surface!

After studying this problem for many years, we have developed a new device (It’s patented! See USP 7,432,827) designed to be much more effective on a wide variety of loop sensors.

Phillip Torrone

Editor at large – Make magazine. Creative director – Adafruit Industries, contributing editor – Popular Science. Previously: Founded – Hack-a-Day, how-to editor – Engadget, Director of product development – Fallon Worldwide, Technology Director – Braincraft.


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Comments

  1. Steve Owens says:

    This is a common problem for motorcyclists as well. The way some of us geek bikers work around it is to mount a hard drive magnet to the bottom of the frame. It’s not too hard: the magnet is strong enough to stick on its own!

  2. captain obvious says:

    I have a steel framed road bike and an aluminum framed bike that easily triggers the sensor on my parking lot gate. Several of my co-workers ride motorcycles and they just stuck a cheap rare earth magnet on the bottom of their rides, says it works great.

  3. Sat says:

    I was tempted to try something like this out when I was getting stuck at traffic lights that wouldn’t turn. Then I read that induction loops can easily be triggered by your bike without any modification. You just need to make sure your wheel is over the inductive loop and you are good to go. The lights that weren’t changing me now do since I know that I need to position my bike just right.

  4. nathan.3dmobility.com says:

    I have a carbon road bike that definitely doesn’t trigger the loops. The rare earth magenet is the way to go. I cut a little divot into the tread of my bike shoes and epoxied the magnet in the sole of the shoe. Works like a charm.

  5. foobar says:

    is what the black gizmo is in front of the rear wheel?

  6. Ed Richley says:

    The reason I developed this is that there are several intersections where wheel placement is not sufficient to trip the sensor. I got tired of laying my bike down in the middle of a highway.
    The “black gizmo” you see is a Basta (Union) generator for night riding.
    I’ve heard the magnet claim a lot, but I have not seen anyone test it scientifically. The loop senors work by sensing the change of inductance of the loop, using a frequency between 20 and 200kHz, usually in a free-running oscillator whose freq gets pulled a little, as the inductance gets changed by induction, with a vehicle present. It’s hard to see how a permanent magnet (a D.C. field) would have this effect. And I’ve seen just as many claims that the magnet doesn’t work. But, if it works for you, go for it. Do you, by any chance, have metal rims?

  7. Anonymous says:

    Pedestrians must pay attention to the WALK/DONT WALK signal when attempting to cross the road.

  8. Eleftherios Kosmas says:

    Wouldn’t just a neomydioum magnet do the job…

  9. weirdguy.myopenid.com says:

    there where actually instructions on how to build one :/

  10. Anonymous says:

    It would constitute infringement if you did built this one. (unless you got a license from the patent owner)

    1. bikerguy says:

      Patent infringement would occur if you went into business using key parts of this patent. You are allowed to build one for research. This is to allow ideas to build on ideas. Improvements or alternatives may be patentable as well.