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-   -   Newbie Question: Light Sensers (http://bikeportland.org/forum/showthread.php?t=3544)

TimmyTwoPedal 04-27-2010 08:22 AM

Newbie Question: Light Sensers
 
So this is a matter of dispute between a friend and myself.

The trick of lowering you bike sideways when you stop at a stop light, does it make the light change faster? Is there a sensor that is able to register the bike and therefore change the light?

I know this question sounds ridiculous, but I need an answer to clear this up. Also if anyone could provide proof, one way or the other.

Thanks a lot!

-TimmyTwoPedal

Bent Bloke 04-27-2010 10:00 AM

I don't know that it changes faster, but it can help the sensor "see" that a vehicle is present. At work we have a gate that lowers automatically at night. I have to lean my bike over on its side in order to trip the sensor that raises the gate. No doubt the same dynamic is at work with traffic signals.

TimmyTwoPedal 04-27-2010 11:35 AM

Dang, I'm actually trying to disprove my friend's theory.

What mechanism does you work use for its gate?
Is it really a metal detector underneath?
Admitted I know very little about streetlights so I imagine that they use a variety of sensors, the question is if this one is being by them in any cases.
Do you know if the sensor you have at your work (I'm guessing a commercial version) is similar enough (or the same as) to a public street sensor?

-TimmyTwoPedal

P.S. I know that there used to be light sensors on the top of specific streets for Emergency vehicles and that these have been replaced in some states by a UV sensor that Emergency vehicles lights trigger; But these are specific to certain routes and usually on busier roads.

Bent Bloke 04-27-2010 12:25 PM

Quote:

Originally Posted by TimmyTwoPedal (Post 23653)
What mechanism does you work use for its gate?
Is it really a metal detector underneath?
Admitted I know very little about streetlights so I imagine that they use a variety of sensors, the question is if this one is being by them in any cases.
Do you know if the sensor you have at your work (I'm guessing a commercial version) is similar enough (or the same as) to a public street sensor?

It's buried in the concrete, so a little hard to tell. ;)

I think the street sensors use electro-magnetic induction to detect the presence of a large object nearby. I assume the gate here at work uses the same method -- there is no pressure cable on top of the pavement, and no photo-sensor along side it.

On the street, you sometimes see painted symbols of a bike over the induction loops, to mark the "sweet spot" for bikes. Usually all you need to do is position your bike at that spot. You should be able to trip most of the lights by locating the induction loop cable (you'll see where the cut in the pavement was sealed), and stopping your bike over the loop. This should work even on signals that don't have the bike symbol marking, but not always. In those cases leaning your bike over should provide a larger target.

I've heard that it's not just positioning that counts, but the duration of the stop. A short stop over the sensor shouldn't trigger the signal, you need to stay there for a bit.

Ante 04-27-2010 12:25 PM

Sometimes in front of a stop light you will see that a thin, circular or diamond-shaped cut was made in the pavement and then filled in with new asphalt. There is a loop of wire under there that detects when a large metal object is over it - I presume it uses magnetic induction.

Those loops are calibrated for cars and often bikes will not trip them. Sometimes leaning your bike over closer to the ground will get more metal closer to the loop and will sometimes cause it to register that you're there. Now if you have some fancy carbon fiber bike you're probably out of luck regardless of how far you lean your bike over to one side.

K'Tesh 04-27-2010 09:17 PM

Say Cheese!
 
Many of the sensors in Beaverton are actually tied to a camera. I've found that to trip those on wet nights is to locate the camera, and shine my helmet light directly at it.

They work when they detect a large change in the values of the pixels in the sensitive areas.

So, if you don't see a diamond, or circular cut, and you know that the intersection is not set by a timer only, look for those cameras.


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