Vehicle, Magnetic Metal Detector

Origional Project Posted on: "Aug 3, 2015"
Latest Update: October 13, 2016,
Added a Video from Chris.

This is a Considerably Different type of Circuit that Detects Vehicles using a Buried Coil.
This is a VERY Stable circuit, Compared to my Car Loop detectors.
This Circuit is a Modified Version of a Commerical made Unit.

This will ONLY Detect the Magnetic Metals, (IRON, NICKEL and COBALT) But I believe All cars and most Motor Bikes have Steel Frames. And the Metal Must be Moving onto or away from the coil, to Trigger the Circuit.

This Detector also Works, Even If the Coil is Laying On Re-Bar or Other Magnetic Metals.

Example As the car moves Over the Coil it Triggers the Circuit. But if the Car Continues to stay Stopped OVER the Coil it will NOT continue to Detect it as it Sits their. However When the Car Drives away again, It will trigger the circuit Again.

So Ideally you put it in your Driveway, in a place where No One Parks.

When you First Apply Power to this Circuit, it takes about 1 Minute before Stabalizing.
   Than you can Calibrate it.

CALIBRATION, Is Simple, As Shown on the Schematic.

This Circuit is for a Real Car or Truck, Maybe a Motorcycle. It is NOT for detecting Small "Model Cars". As it does Not work well on Small Objects at any great distance.

The Coil is wound on a 12 Inch or Longer Piece of 1/2 or 3/4" or 1" Diameter, piece of Water Pipe or Fence Post pipe. And the Coil I wound consists of 4,700 Turns of 40 AWG Wire. (YES, Forty Seven Hundred Turns.) My Coil measures 210 Mhy of Inductance.

My Laithe won't hold a Piece of Pipe longer than 14 Inches, but I suspect that a Longer Pipe would give a Better Detection Field. I Recommend using a Minimum, 3/4 inch diameter pipe and you Might Try a longer, 24 Inch Long Pipe for a larger field of detection. Also, Using 5,000, 6,000 or MORE Turns of wire may Also Work Better on either the 12 inch or a Longer pipe.

If Wanted, You can use a bigger gauge of wire and it will work equally well. The Wire should be Wound in Fairly Evenly LAYERS over about 11 Inches of the 12 Inch Length.

Before Burying the Coil, It should be WELL POTTED in EPOXY Resin or some other Product to Protect the Coil
and ALL WIRE CONNECTION from Moisture.

The Coil gets Buried about 2 or 3 inches deep, where its Needed. The Circuit should go inside your House or Garage so it is protected from the Weather.

For Shorter Distaces between the Coil and Circuit Board, No special wire is needed. For a long distance, Than probably use a Coax cable to the coil.

LIGHTNING PROTECTION. Some people using this type of detector have complained that their coils were damaged by Lightning Strikes. If this is a Problem, I would recommend putting the Coil inside an Aluminum Tube,
Or placing a Inverted "V or U" Shaped piece of Aluminum Directly Over top of the Coil.

I Can't Guarantee this will work to totally protect it, But I Believe it Will.

I Can supply a PCB and Parts for this Project. Price Depend on: Exactially What parts you want, and Where it gets mailed to.

Also I can supply a Coil for about $20.00 USD. The Shipping Cost to the USA is about $17.00. However, Shipping a coil Overseas is Considerably MORE EXPENSIVE.

"Back to my Projects Page"

A Video from Chris in Minnesota with his Loop Detector-3
that he put together and installed in his driveway.

Detector-3 Schematic.

Detector-3 PCB.

Overlay Picture.

NOTE: The 7806 Voltage Regulator can be Replace with the Smaller "78L06",
as Current Draw on this circuit is Less than 80 mA.

A Typical Coil.

I Wound this coil on my metal Laithe at About 1120 RPM, on a 3/4 Inch OD Diameter, Water Pipe.

This Finished Coil.

I Covered this coil with a Fibre Glass Cloth, Than Saturated the Cloth in 15 Minute Cure, "Epoxy Resin". So it is Considerably Protected against Damage And against Moisture.

Another Coil I Built for Another guy
with More Turns and somewhat more Sensitive.
Wound on a 1.375 Inch Diameter Pipe and Coated with Varathane to Seal and Protect it.

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