Vehicle Loop Detector

[chemelec]

Due to Many requests from persons unable to find this on the internet, I designed up this circuit this morning.

After all, it is a Metal Detector.

And by adjusting the Frequency of oscillation Many Sizes of Coils are Possible.

It May also be a Useful Circuit for Finding Meteorites.

http://www3.telus.net/chemelec/Projects/Loop-Detector/Loop-Detector.htm

Comments Always Wecome

Take care...Gary

[Esteban]

Hi Gary

Thanks. Your interesting project covers a hole as for this type of detectors.

The most simple and effective I hear consit in a buried large coil (very good isolated) connecting in serie with a lamp and 220 V relay, this was a detector only for car (big mass). And had an electromechanical counter. This is a detector for 220 V!

[chemelec]

If anyone is Interested, I have now Updated this article with a PCB Design as well as a Picture Overlay of the board.

http://www3.telus.net/chemelec/Proje...p-Detector.htm

Take care....Gary

[Ferric Toes]

PI Vehicle Detector.

The Plessey company had a patent (probably early 70's) using 1/2 wave rectified mains power as a TX for a vehicle detector loop. Presumably transformed down! Same coil as RX with simple sampling/integrator system feeding a comparator, which operated a relay. No tuning required and you could get away with just one turn. Also immune to interference from power cables in the road as the TX was perfectly synchronised.

Eric.

[Sean_Goddard]

Hi Eric, Call me sometime we MUST arrange that beer before I disappear for ever (BTW this may happen a lot sooner than anticipated).

Phone number is on my website, but I'll call you back if you leave me a message and phone number

[chemelec]

The Plessey company had a patent (probably early 70's) using 1/2 wave rectified mains power as a TX for a vehicle detector loop. Presumably transformed down! Same coil as RX with simple sampling/integrator system feeding a comparator, which operated a relay. No tuning required and you could get away with just one turn. Also immune to interference from power cables in the road as the TX was perfectly synchronised.

Eric.

That may well be, But I can't find anything on it, not even searching US Patents. But Maybe its just too old of a patent for the site I searched.

Either way, My circuit is Quite Stable and it will probably also work with a large single turn coil.
And it can be used with the Power Mains or Battery operation.

I Know it will be useful to some people as some have already built it and commented on it.

[dete]

Hi
It’s about a year since I signed in. I have to write a post so my user won't be deleted...

In my country there are some traffic light controlled by such a metal detector. Its loop is about 1,5 x 2 m and is inserted in the cut in the tarmac.
It is not sensitive enough to detect me on the bicycle so I always have to go to the pole and push the button like a pedestrian. It annoys me.
Is there any way to produce »false« signal with a reasonably small and light gadget.

[Carl-NC]

That may well be, But I can't find anything on it, not even searching US Patents. But Maybe its just too old of a patent for the site I searched.

Plessey is a British company, so the patent is likely British. BTW, nice little circuit you did, very simple solution!

Is there any way to produce »false« signal with a reasonably small and light gadget.

If you were to make an oscillator+coil at the same frequency as the traffic detector, then you might be able to create enough interference to trip it. An alternative is to add a large metal plate to the bottom of your bike.

- Carl

[Max]

Hi
It’s about a year since I signed in. I have to write a post so my user won't be deleted...

In my country there are some traffic light controlled by such a metal detector. Its loop is about 1,5 x 2 m and is inserted in the cut in the tarmac.
It is not sensitive enough to detect me on the bicycle so I always have to go to the pole and push the button like a pedestrian. It annoys me.
Is there any way to produce »false« signal with a reasonably small and light gadget.

Hi,
probably is a pulse induction detector, cause I think wouldn't be nice having e.g. a BFO , or a TR-vlf or TR-hf to detect vehicles...and controlling the traffic light due to interferences bfo or vlf could suffer from in a street (think e.g. at electrical lines buried under the street itself, telephone cables, broadcasting radio channels next there , police radio signals etc
Maybe your bicicle is not detected due to the low iron/magnetic materiarls content.

I guess that cars are detected due to their flat metallic floor (large) facing coil.

Anyway, can you make a test ? When arrive to the traffic light just try to inclinate it for say 15-30°. If there is enough conductive pattern inside the mag flux (area seen by detector), and detector is a PI type, your bike could be detected that way! Even if it is made of magnesium-aluminium alloy.
Simple test, but who knows... maybe works!

Best regards,
Max

PS "It’s about a year since I signed in. I have to write a post so my user won't be deleted..."
another good reason to post here

[amtech2005]

Vehicle Loop Detector

There were a few articles on Vehicle loop detectors a few years back "complete with schematics" and it was on the internet. What probably happened was someone bought the rights so they can manufacture these units. There is a company that manufactures a Vehicle Loop Detector and it is switcheable between 20 and 180 khz and its on a pdf file. Now that a can of worms has been opened I am searching like crazy to find Schematics. I thought I saw an article on this exact Subject in Pop-Tronics or the older Popular Electronics . As soon as I find a Schematic I will post. Eugene

[Ferric Toes]

Somewhere in my "junk" boxes I have the electronic unit from a traffic light vehicle detector. Also design information for the relevant coils. Can't remember much about it, but it definitely wasn't PI. When I find it I will post the information. Same with the Plessey patent which I have somewhere.

Eric.

[JC1]

Signal Sorcerer

Hi Eric,

A traffic signal-controlling inductive loop is simply a coil of wire that has been buried just beneath the road's surface. The coil is then covered with black tar or rubber for protection from the elements and traffic wear. When a small electrical current is run through these coils, as per the laws of magnetics, they become electromagnets. The inductance of these loops is then measured with a meter. The units of measure are called "Henrys." When ferrite (iron – not aluminum or titanium, etc.), or ferrite containing materials such as some steels, breech the 2)field of the loop, the inductance rises. The signal controllers and switches, which tell the traffic light to cycle, are linked to the meter measuring the inductance of the loop. When the inductance of the loop increases by a preset amount, the timer is engaged and the light initiates its cycle based on the current timer setting. The human body, fiberglass, plastic, aluminum, titanium, rubber and most other substances have almost no effect at all on the level of inductance. 3Ferrite most substantially increases inductance. Ferrite is present, in varying degrees, in almost all steels.

2 -The field of an inductive loop extends above the loop, beneath it, and to the sides of it. The loop's field strength reduces rapidly the greater the distance from the plane of the loop: ferrite that is 4" above the loop has a significantly greater effect on that loop's inductance than the same ferrite 6" above the loop, which has a significantly greater effect on that loop's inductance than the same ferrite 8" above the loop, and so forth. Hence, ferrite containing materials that are perpendicular to the road's surface do not influence inductance as much as those running parallel to it, per se.

{Ferrites !!!}

Q- Will the Signal Sorcerer® traffic light tripper trip every type of traffic signal controller?
A – The Signal Sorcerer® traffic light trigger is engineered to work only on electromagnet-based systems (inductive loop systems). This covers the vast majority of systems employed in the US today - as well as in many other countries.

http://www.signalsorcerer.com/technical.html

I've had to run many a red light that

would not change. On a motorcycle.

[amtech2005]

Vehicle Loop Detector

I have been Searching for a couple of days now for any Schematics. The only thing I came up with was this photo , a simple PCB Board of a Vehicle loop Detector. No Schematics yet , sorry . Eugene