The Cure for Red Light Blues?

[Woody14619]

You can also trigger such stubborn lights by shifting the car to neutral and revving the engine a couple times. The field spike is usually enough to trigger it. But really, if a particular light is giving you problem, good odds it's giving bike operators trouble too and should be reported.

[JD10367]

Some pads can be triggered by backing up and going forward again. If you know it's a problematic pad, and you're the only car, when you come to a stop immediately put it in reverse and drive off the pad and back on again. That might work.

[BobDiaz]

The loop is an inductor and is used in an LC (Inductor - Capacitor) or LR (Inductor - Resistor) circuit to an oscillator. When any Ferrous metal is moved close to the coil, the inductance of the coil increases and the frequency of our oscillator decreases. The drop in the frequency in the oscillator tells the traffic light that there is a car waiting.

I just don't see how a small, but strong magnet will change anything in this system. Keep in mind that there are a lot of hoaxes on the internet and this could be one of them. (The video of using cell phones to make popcorn pop is a good example.)

The problem is not the technology, but the sensitivity of the system. Someone from the city may not have adjusted the system properly and it takes a lot of ferrous metal to trip the detector.

I'd love to run several tests on our traffic lights where I live, but right now I have my hands full teaching electronics classes at El Camino College. Maybe during the summer break, I'll run some tests....


Bob Diaz

[John_H]

Bob -
Different discriminator circuits may behave differently. The addition of the magnet entering the loop could add a significant low-frequency push of the sine-wave one direction. If the signal isn't filtered for the frequencies of interest, a simple positive peak detector could be fooled. Yes?

[BobDiaz]

I guess it all depends on how the circuit is designed. A PLL (Phase Lock Loop) would not be fooled, but a simple low pass filter looking for a peak voltage could be fooled. I'd have to run tests to see, but that has to wait until after June 12....


Bob Diaz