What are these objects on traffic lights?

[Gilligan]

[IMG]file:///C:/Documents%20and%20Settings/Administrator/Desktop/for%20RadioRef/Antenna%201.jpg[/IMG]What are these objects on OKC traffic lights? One looks like some kind of sensor (for emergency lights?) and the other looks like WiFi antennas.

[Jay911]

The one beside the red light (in the left hand image) is an Opticom traffic signal pre-emption receiver. Emergency vehicles will have strobe lights, sometimes visible light, sometimes infrared, that will be received by these devices, triggering the lights in that direction to go green and everything else to cycle quickly to red. The light will be held green for as long as the strobe is visible - which sometimes causes problems if the truck parks in sight of the intersection and the crew forgets to shut off the Opticom sender. (The sender is supposed to automatically shut down when the park brake is engaged, but not all agencies wire it up this way.)

The box on the other picture could be anything from WiFi to MOTOMESH networking. (MESH network services kind of operate like WiFi does, except that every node in the system can carry traffic for another node, making it more like the Internet as a whole - so if you're out of range of the box on that light pole, but in range of a cop car that is in range of the light pole, you still have coverage.)

On top of the light housing itself is the photocell which detects when the sky is dark enough for the lights to turn on.

[Jay911]

Here's a closeup of an Opticom receiver.



The sensors are in the large(r) black housing of the device itself - the long flute-like shields prevent flashes from cross-traffic from triggering the light for the wrong direction.

I'm not sure why this model has 2 flutes. Maybe one is visible light and one is IR.

[robynsjw]

http://www.radioreference.com/forums...eak-areas.html

Here Sparky gives a good description of what they are.

All the opto-receivers I've paid attention to in Edmond have been the duals. Possibly for backup purposes? One goes out, the second still works, and an alarm goes off somewhere for the first to be replaced? Then that intersection doesn't have a lapse in coverage.

[kc8svs]

.......

running around the house getting every light and IR light that I own just in case I'm late for a meeting in OKC...

[robynsjw]

When these were first installed in Edmond I was working nights and saw a paper carrier approach one flashing his headlights real fast, and the light changed for him. Don't know if he was lucky with the flashing or the light was changing anyway... He was lucky EPD didn't see him, I doubt there's a specific law against that, but they could make his driving life miserable...

[eharlow]

That's an old rumor on flashing your headlights....at least now days. The flash rate frequency is ultra fast...almost so fast you don't see it flashing. Edmond has recently been upgrading their receivers to where they'll only change for emitters with serial numbers that the City of Edmond has programmed into the system. Apparently there were some wreckers with opticoms running around Edmond and changing the lights for the direction they were traveling.

[car2back]

I know someone, who happens to be a police officer and ham radio operator, that rigged up a strobe w/ an infared filter behind the grill of his car to attempt to trip these things.... supposedly it worked, but would just change the lights to red all directions, so there was really no use for it.

[Freqed]

Originally Posted by eharlow

Edmond has recently been upgrading their receivers to where they'll only change for emitters with serial numbers that the City of Edmond has programmed into the system.

That's some good technology right there, I remember when Tulsa first got their's and the station right next to my work was out there setting up the strobes in the trucks for the receiver to see and where having a hell of a time. I work with all kinds of emitters and receivers @ work and if there not just right they're useless.

[plaws]

Originally Posted by Jay911

Here's a closeup of an Opticom receiver.\
The sensors are in the large(r) black housing of the device itself - the long flute-like shields prevent flashes from cross-traffic from triggering the light for the wrong direction.

I'm not sure why this model has 2 flutes. Maybe one is visible light and one is IR.

Don't know why there are two, either. The old style (from the 1970s - 3M's Opticom ain't new) sensors were smaller and had one "sight" facing each direction and looked much more like a rifle sight.

Looks like 3M sold the product line: Opticom IR

They were originally visible light, but I've only seen IR in the last decade.

In Chicagoland, they add a white light next to them. Solid in one direction, flashing in the other. That way apparatus approaching from different direction know who "has control" of the intersection.

[Secret_Squirrel]

Originally Posted by car2back

I know someone, who happens to be a police officer and ham radio operator, that rigged up a strobe w/ an infared filter behind the grill of his car to attempt to trip these things.... supposedly it worked, but would just change the lights to red all directions, so there was really no use for it.

That's goofy as hell. Since it is goofy, I'd bet the person that you are referring to is "L.H."

[skywatch]

Now all we need is a stop light in town. Does it work on stop signs as well? lol!

[GTO_04]

Originally Posted by eharlow

That's an old rumor on flashing your headlights....at least now days. The flash rate frequency is ultra fast...almost so fast you don't see it flashing. Edmond has recently been upgrading their receivers to where they'll only change for emitters with serial numbers that the City of Edmond has programmed into the system. Apparently there were some wreckers with opticoms running around Edmond and changing the lights for the direction they were traveling.

They're encoded so unless you have the right codes or a special test code you won't be able to trip them. There are several possible combinations so it would be difficult for the casual hobbyist to hack them. The transmitter is a short pulse Xenon flashtube to get the long range distances. They slap an IR filter over some versions (for undercover LEO cars) to make them less visible. The fire engines I've seen with Opticom transmitters just have a Xenon flashtibe with a reflector in a chrome housing. In normal operation they look just like another strobe flasher.

GTO_04