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Simple metal detector circuit

  1. Aug 9, 2017 #1
    Hello, I am a civil engineering student undertaking a project to investigate the effect of pipes and pipelines beneath the ground on the urban city environment above. In order to proceed I am designating a simple metal detector. Due to low depth capability of all commercial metal detectors mine has to be able to detect pipes several feets under the ground.

    Here I am seeking information on how I can possibly alter this simple metal detector circuit so it can be run using 100V input instead of 6-12V? Please consider the attached circuit.

    Thank you

  2. jcsd
  3. Aug 9, 2017 #2
    You get there from here.
    That circuit uses a LM555 timer to create an audible signal that changes based (I presume) on that 10mH inductor - the only part that might be the detector loop.
    There is no 100V version to the 555, and even if there was, it wouldn't help you.

    The changes that you would need for detecting a pipe deep under ground might involve a much larger loop - assuming that it was practical at all - which it probably isn't.

    The technology used for detecting thing like this Ground Penetrating Radar. https://en.wikipedia.org/wiki/Ground-penetrating_radar
  4. Aug 9, 2017 #3


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    Do you mean you want to plug it into a 120Vrms wall socket to power it? Or are you just looking to make a more sensitive detector?
  5. Aug 9, 2017 #4
    I mean I want to plug it into a 120Vrms with much bigger loops, not necessarily making it more sensitive but making so it can detect at greater depth since pipes are few feet under ground.
  6. Aug 9, 2017 #5


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    seriously !!?? you are well out of your depth here. .... maybe you should have done electrical eng rather than civil eng :wink:

    ground penetration depth is more dependent on frequency than voltage in the coil ( tho it will have an effect)

    using a 120V circuit is just incredibly silly
  7. Aug 9, 2017 #6


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    As @davenn says, just trying to increase a voltage will not do much on its own. To make a more sensitive sensor, you would need to do a number of things all at once.

    But of course, that has all been done by others before, so you should be looking at the standard commercially-available options. Can you post links to the most sensitive detectors you have found? Do you understand the reasons that ground-penetrating radar is used for this? Do you know what percentage of underground pipelines are metal versus (non-conducting) concrete or PVC?

    And except for underground natural gas and petrol lines, you will get the best info by just contacting the appropriate utilities (water, sewage, etc) and asking for maps of the pipelines...
  8. Aug 10, 2017 #7


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    You can use a 5V supply to power a device that is plenty sensitive enough. In any such devices that are available and mains powered, the very first thing in the circuit is a voltage converter (power supply) to give the actual measurement circuit a low voltage DC supply (5V or 12V). Isn't that what you have for all your personal electronic devices? (Plug in the wall that gives you 5V.)
    To detect stuff at significant depths you will definitely need a pretty large coil - about the same diameter as the depth you are looking (imo). You have to plot the results over a large grid with long baselines and observe peaks and troughs in your signal output.
    If this is a pukka project then you will of course need to search for information about the topic. PF cannot be relied on to have a "Tame Detectorist" on tap. 'We' have a very broad experience of electronics and our opinions are (often) pretty well informed and we are (so it seems) fairly expert at using Google and other search engines.
    There is absolutely no point in launching out into building something as simple as you propose (I think the circuit you posted is the same as the very first Google hit I found.). You first need to find out what sort of specification is required and spend a long time on research before lifting a soldering iron!
  9. Aug 10, 2017 #8


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  10. Aug 10, 2017 #9

    jim hardy

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  11. Aug 12, 2017 #10


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    Surely, if the pipes effect the “urban city environment above” they must be detectable.
    If you cannot detect the pipes, then how can they effect the city environment above?

    You are assuming that pipes are made from metal. Plastic is now more common.
    What effect do you expect the pipes to have? Can you use that effect to detect them?

    Underground pipes and cables are usually traced by energising them with a low voltage audio frequency. The AC current that flows along the conductor causes a magnetic field that can be picked up with a hand held loop and detected with a tuned receiver. Changing the orientation of the loop increases the accuracy of the tracking.
  12. Aug 14, 2017 #11


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    Detecting their presence is not the same as locating their position etc..
    It is a valid idea to correlate the presence of pipes etc. with conditions on the surface - drainage, plant growth etc.
    Last edited: Aug 14, 2017
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