Metal Detector Electronics Project

[Wesley Godinez]

Metaldetector is a very common device that is used for checking persons, luggage or bags in shopping malls, hotels, cinema halls, etc. to ensure that person is not carrying any metals or illegal things like guns, bombs etc. Metal Detectors detect the presence of metals.

There are different types of metal detectors like hand held metal detectors, walk through metal detectors and ground search metal detectors. Metal detectors can be created easily and the circuit for a basic metal detector is not that complex.

TDA0161 Proximity Detector IC: TDA0161 is a Proximity Detector IC manufactured by STMicroelectronics. It can be used detect metal objects by detecting the slight changes in the high frequency Eddy current losses.

The TDA0161 IC acts as an oscillator with the help of externally tuned circuit. The changes in supply current will determine the output signal i.e. current is high when a metal object is near and it is low when there is no metal object.

There are three main parts in the metal detector circuit: the LC Circuit, the Proximity Sensor , output LED and the Buzzer. The coil and the capacitor C1, which are connected in parallel, will form the LC circuit.

LC Circuit: LC circuit has inductor and capacitor connected in parallel.This circuit sarts resonating when there is same frequency material near to it. The LC circuit charges capacitor and inductor alternatively.When the capacitor is charged fully ,charge is applied to inductor.

Inductor starts charging and when charge across the capacitor is nil, it draws charge from the inducutor in reverse polarity. Then inductor charge is reduced and again the process repeats.Note inductor is a magnetic field storage device and capacitor is electric field storage device.

Proximity Sensor: The proximity sensor can detect the objects with out any physical interference. The proximity sensor will work same as infrared sensor, proximity also release a signal, it will not give output unless and until there is no change in the reflected back signal.

If there is a change in signal it will detect and give the output accordingly. There are different proximity sensors for example to detect plastic material we can use capacitive type proximity and for metals we should use inductive type.

The LC Circuit, which consists of L1 (coil) and C1, is the main metal detector part of the circuit. With the help of this LC Circuit, which is also called as Tank Circuit or Tuned Circuit, the TDA0161 IC acts as an oscillator and oscillates at a particular frequency.

When the LC circuit detects any resonating frequency from any metal which is near to it, electric field will be created which will lead to induces current in the coil and changes in the signal flow through the coil.

Variable resistor is used to change the proximity sensor value equal to the LC circuit, it is better to check the value when the coil is not near any metal object. When the metal is detected, the LC circuit will have changed signal.

The changed signal is given to the proximity detector (TDA 0161), which will detect the change in the signal and react accordingly. The output of the proximity sensor will less than 1mA when there is no metal detected and it will be around 10mA (usually greater than 8mA) when coil is near to the metal.

I built it and it works pretty good. Not sensative enough to use for digging up treasures at the beach, but I think it will be useful for finding that lost bolt or screw in the grass. Next step will be building a soldered up version and mounting it on a handle. No problem finding the IC on ebay.

I have a need for similar circuit but the only difference is, the circuit I need should function the same way as this one does IN MAGNETIC FIELD. Do you know if this should function the same way under the influence of magnetic field?

So that would be an interesting items, would require batteries maybe and players could scour and find some really unexpected and old/new stuff from grounds if they are lucky enough. What do you fellow survivors think about this?

Perhaps it would be useful for finding scrap metal, or buried pipes (though I don't think any/many underground pipes would be made of metal - more likely concrete, PVC, or ceramic), but the frequency of finding useful objects would probably make it more like searching for a needle in a haystack.

You'd be surprised. I had a bright orange plastic metal detector when I was younger. Ran off a 9V battery, clearly made for kids, but it worked pretty well. Plus, if you know what you're doing, it's reasonably easy to make a metal detector from electronic components and some wire.

As for a use in Zomboid? Stripping for electronics, or rewiring as a sensor in some electronics project. Most sets of traffic lights have a magnetic loop running across the traffic lanes (much like a metal detector) for sensing if cars are stopped and waiting to pass through the intersection. That's also why gluing strong magnets to a bicycle frame is a good idea; The strong magnetic field is detected by the loop, allowing regular bikes to be counted in the traffic light's logic. With a bit of jiggering, I could see a metal detector (or the guts of one) serving as a vehicle sensor, opening gates for passing vehicles, detonating mines, or something. Be better than using pressure plates, seeing as hordes would probably weigh enough to set one off.

Mine detection? Probably not going to work. Modern landmines are mostly plastic, specifically to avoid setting off military metal detectors. Could work well for detecting unexploded ordnance though. With all the battlefields (post zombies of course) and abandoned target ranges in the Kentucky area, there's bound to be a few hot potatoes waiting around for some poor bugger to step/kick them.

Finally, buried treasure! Perhaps a survivor buried a cache of ammo, perhaps a survivalist scattered cheap guns over the landscape long before Z day and forgot about them (it's been know to happen). But, the best, and most common, kind of buried treasure would be finding nails, screws, fish hooks and the like buried in soft sand/mud around garages, river banks, and so on. Imagine if someone lost a multitool when fishing and it got buried in the sand. If it's a decent non-cheapie one, it's going to be mostly rust proof, so you'd be able to use it to some extant after digging it up. Loose railway spikes, lying hidden in the ballast around/under railway tracks could be useful too.

I still think the frequency of finding non-worthless 'scrap' would realistically be a bit low to make it worthwhile... then again I spent countless hours on the Gameboy digging holes in Zelda in hopes of finding stuff.

Hello! First of all i have to say that I've only just started exploring the world of Arduino and was startled by the possibilities! Making an EMF detector got me thinking about Arduino's capabilities...

I have a rather basic, but highly praised VLF metal detector. Its a Tesoro Compadre if anyone is interested... It does have a discrimination circuit, but it works on exclusion principle so by turning up the discrimination pot you're blocking off iron first, then supposedly "foil" then pull tabs etc. VLF detectors use phase shifting to discriminate between metals (How Metal Detectors Work HowStuffWorks) and whereas more advanced models can tell you what the signal is likely to be, mine has no visual indicators on it.

Turning the discrimination up reduces sensitivity, so instead i was wondering if it would be possible to use Arduino to either analyse the amount of phase shift as the phase demodulator does to then tell me what the signal is likely to be, or to use it in conjunction with the built in discrimination circuit to do the same but identifying rather than discriminating...

Hey Roger, yup had a look on the forum before i posted and found a couple of discussions on making a metal detector but the talk there is mostly about pulse induction detectors and starting from scratch and i couldn't find anything VLF discrimination related. I have a rather basic knowledge of electronics so starting from scratch isn't really an option and i already have a basic metal detector, just thought maybe it could be as simple as jumping a few wires from the detector circuit to the Arduino and getting it to do some signal processing... But even if its not as simple as that, i would still rather try to add the identification function to my metal detector than attempt to build one...

Any luck with your idea? I'm in a similar situation, just a different metal detector brand/model. I have general experience with microcontrollers and have read about the topic and think I know just enough to be dangerous.

You could use the ADC to detect the zero crossings of the search and receiver signals, but may need to raise the overall voltage of the signals so top (+) to bottom (-) swing is seen by the ADC. But with one ADC, you'd have to switch between the search signal (which I think would be pretty uniform and would require sampling less often) and the receiver signal, measure the times at which the signals crossed zero and from that determine the phase shift. Also, the voltages involved might need to be limited to 5v or 3.3v max- I'm not yet familiar with the arduino ADC.

Skimming over some MD patents, an easier way to do it might be to take in the signals from above, convert them to binary so the arduino (mc) only receives the positive side of the signals when they reach a certain lower voltage. This makes the ADC unnecessary. Then when the search signal input goes from low to high, an interrupt is called, the mc starts counting until the receive input goes low to high. If no receive low to high is received, the mc will reset the count when the search signal repeats. At this time it could use the count to determine the time period of the search signal. I would think this would be enough to solve for the phase shift of the receive signal and hence the target in the ground.

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