a stupid question

I'm pretty sure that you just need the perimeter to be conductive. So a

Back when my knees allowed me to commute by bicycle, I could reliably trigger traffic lights by centering myself over the pick-up loop and angling the bike down (by about 45 degrees) so that the main triangle was laid over the loop. This worked quite well. It may be challenging to do this with a Harley or a Gullwing, however.

This product has an Amazon 4 star rating, but also some reviews say it doesn't always work. One guy had 3 troublesome lights on his route, it worked on two of them.

Mikek

use it for baking cookies when not testing the loop.

why is that a problem? is your car made of ferrite?

this does suggest that the sensor is looking for a decrease in inductance.

does steel work correctly ?

how about a few metres of copper wire in a loop,

when riding a push bike I stop with the front wheel over, and aligned with the cut where the loop is, for me it works every time.

I've seen a traffic jam caused by a loop of steel packing strap lying on one sensor, messing up the traffic light timing near the end of a freeway.

My thinking was that ferrite would work well because it should shift the frequency more than other metals. (the object is to find something that reliably triggers the loop, and doesn't take up a lot of room)

Sheet metal works well, but misses out in the small compact design goal. Type of metal, either doesn't matter or matters very little.

I wish I'd thought of the idea one responder had; an open loop then shorting it to make it trigger the detector - then I could have buried both the detector loop along with the test loop.

But that gives me another idea that aught to work - a small capacitor or inductor that I can switch in parallel with the loop to shift the frequency. Ferrite donut with a turn or two of wire is small compact and can stay inside the detector housing with just a switch on the outside. I'll give that a try as soon as it gets light enough outside.

As a testing device a large loop still needs support and a frame of some sort.

Thanks to you and others I have a few more things to try. thanks guys

It is just a magnet and I've already tried some pretty damn strong magnets to no good effect. But then I haven't really tried them on the motorcycle and the magnet + frame might matter more than the magnet alone.

I do keep a 1" dia X 1/2" neodymium stuck on the oil drain plug to slurp up any particles that are floating around in the oil.

And a small toroid inductor that parallels the loop may achieve the same thing. So thanks for that idea.

I hear you. I'd ride my bicycle to keep my heart rate up at 140 for an hour a day, until my knees started getting painful after several years... Now I paddle a kayak 4 miles every day - so I guess my wrists or fingers will be the limiting factor some day.

Exercise makes everything else work better when one starts to show signs of age...

park a car on it.

w.

as you have access to the wiring you could short terminals that connect to the buried loop: the sensor seems to respond to reduced impedance.

it may not be a free running oscillator, it may be a fixed frequency transmitter and the load current monitored to detect metal

you might just need the switch :)

Ok empirical results: A dead short in the loop at the controller will briefly twitch the output relay (so it triggers the timed lights I've added) but then the controller tells me there's a bad loop (inductance too low so there must be a short).

A small inductor I had laying around (unknown L) will fool it into triggering just like a vehicle was present.

GREENLIGHT/dp/B00D9GZSF4

AFAIK, a magnet isn't going to have any more effect on an inductive pickup than an identical chunk of the same alloy that's not magnetized. Simply put, the inductive coil is working at AC, and the magnet only affects DC.

A magnet strong enough to affect the electrical behavior of your (steel) frame would be enormous.

My uncle worked on one of the earliest inductive-pickup systems; his "test car" was just a one-foot square sheet of aluminum (but, his pickup coil was only about 18" in diameter, presumably with lots more turns).

There is probably some AC signal that you could pump into a small coil that would fool the loop sensor.

Back in the day working with Mot used to work on the drive thru stuff at Roy Rogers. I just placed my little fold up hand truck on the loop. Worked every time.

Loop diameter and target diameter ratio probably counts for more than anything else. I tried a big heavy pipe wrench, crowbar, etc on the small loop without it seeing it, but a tin can lid was triggering it anywhere near the loop.

I wouldn't expect a magnet to have any effect on an inductive loop sensor so I'm leery of the advertising claims of the one for sale on Amazon. But there's inductive loop sensors and magnetometer sensors. The magnetometer only senses moving metal/magnets so I wouldn't think they'd find much application in traffic lights.

No doubt. The loops themselves have to reject 60 cycle hum so there's probably a notch or high pass filter. The loops change frequency slowly over time with temperature and rainfall and the microprocessor has to compensate for that and only see the relatively faster changes a vehicle makes. They do tune themselves too - switch capacitors in and out to set the frequency and there's a switch selection for high medium and low frequency to minimize interference with nearby loops.

But a pick-up loop on the bike sensing the frequency could output a burst of some powerful but slightly different frequency... I'm not looking for a new career. If my MC can't make it trigger what hope do bicycles have?

And the DOT suggestion that one ride close to the edge of the loop? The center of the loop works better IMO. Dealing with the bureaucracy at DOT is another pain. It takes several phone calls or emails to get them to reset and recheck the sensitivity and things will be fine for a time, until someone complains because people driving cars will "cut the chord" if there are no vehicles present in the perpendicular lane and also trigger the light.

I'm sure the technology will improve enough to fix the problem... eventually...when they find the money.... make the effort...

I posted this 12 hrs ago and don't see it, may end up with a double.

What is the frequency of operation?

How about a ferrite rod?

A ferrite rod with shorted turns?

How about a tuned ferrite loop?

I'm tempted to go play with ferrites at a traffic light!

Mikek

Large plastic coated ferrite rods. >

But you can probably do it cheaper stacking potcores. I have some big a$$ potcores, 3C81 material >

From my original post. Ferrite was the first thing I tried, screws up the detector so that it causes it to trigger ON when the ferrite is removed from the small test coil and has no effect on the 12' diameter loop. Have to press the reset or cycle the power to get it working so it is on when metal is detected.

I used a stack of 1/2" ID 1-3/8" OD stacked on a 1/2" CPVC water pipe

I didn't try a shorted turn on ferrite though...

The loop pretty much just sits there so I don't expect to use a piece of sheet metal too often - I really wanted something to test the stuff I've added which turn on when the detector turns on.