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  • scarborough circuit

    Hi all. I'm new to this forum. Here's a schematic sent to me recently by
    Rev. Tom Scarborough.

    "I hope this helps. Incidentally, here is my most powerful CCO design -- which requires a radio. It appeared in Elektor magazine."


    With kind regards,
    Thomas.

    To the best of the author's knowledge, the metal detector shown in Fig.1 represents another new genre. It is presented here merely as an experimental idea, and operates in conjunction with a Medium Wave radio.


    If a suitable heterodyne is tuned in on the Medium Waves, its performance is excellent. An old Victorian penny, at 180mm, should induce a shift in frequency of one tone through the radio speaker. This suggests that the concept will match the performance of induction balance (IB) detector types, while employing a fraction of the components.


    In principle, the circuit is loosely based on a transformer coupled oscillator (TCO), a well known oscillator type. This essentially consists of an amplifier which, by means of a transformer, feeds the output back to the input, thus sustaining oscillation. On this basis, the author has named the detector a Coil Coupled Operation (CCO) Metal Detector.


    In fact the circuit shown in Fig.1 would oscillate even without L2 and C1. However, in this case one would have nothing more than a beat frequency operation (BFO) detector.


    Coil L2 is added to bring the induction balance principle into operation, thus modifying the signal which is returned to the output, and greatly boosting performance.


    This does not mean, however, that we are dealing strictly with an IB detector type, since the design requires a beat frequency oscillator for detection. Also, unlike IB, its Rx section (L2) is active rather than passive, being an integral part of a TCO. Nor is this strictly a BFO type, since its performance far outstrips that of BFO, and of course it uses two coils.


    Search oscillator IC1 oscillates at around 500kHz, depending on the positioning of the coils on the search head. The presence of metal induces changes both in the inductance and coupling of the two coils, thereby inducing a shift in oscillator IC1's frequency.


    The output (pin 6) is taken via a screened cable to a Medium Wave radio aerial. A crocodile clip termination would make a convenient connection.


    The two coils are each made of 50 turns 30swg (0.315mm) enamelled copper wire, wound on a 120mm diameter former. Each has a Faraday shield, which is connected to 0V as shown.


    The coils are positioned on the search head to partly overlap one another, in such a way as to find a low tone on the best heterodyne, which should match the performance mentioned above.


    Oscillator IC1 will sustain oscillation no matter which way the coils are orientated - however, orientation significantly affects performance. The correct orientation may be determined experimentally by flipping one of the coils on the search head. Ideally, the coils will finally be potted in polyester resin.


    The CCO Metal Detector's search head offers a wide area of sensitivity, so that it is better suited to sweeping an area than pinpointing a find. As with both BFO and IB, it offers discrimination between ferrous and non-ferrous metals, making it well suited to "treasure hunting".
    Attached Files
    Last edited by germeten; 11-17-2006, 12:00 AM. Reason: cleaning up

  • #2
    Originally posted by germeten View Post
    Hi all. I'm new to this forum. Here's a schematic sent to me recently by
    Rev. Tom Scarborough.

    "I hope this helps. Incidentally, here is my most powerful CCO design -- which requires a radio. It appeared in Elektor magazine."

    With kind regards,
    Thomas.

    To the best of the author's knowledge, the metal detector shown in Fig.1 represents another new genre. It is presented here merely as an experimental idea, and operates in conjunction with a Medium Wave radio.


    If a suitable heterodyne is tuned in on the Medium Waves, its performance is excellent. An old Victorian penny, at 180mm, should induce a shift in frequency of one tone through the radio speaker. This suggests that the concept will match the performance of induction balance (IB) detector types, while employing a fraction of the components.


    In principle, the circuit is loosely based on a transformer coupled oscillator (TCO), a well known oscillator type. This essentially consists of an amplifier which, by means of a transformer, feeds the output back to the input, thus sustaining oscillation. On this basis, the author has named the detector a Coil Coupled Operation (CCO) Metal Detector.


    In fact the circuit shown in Fig.1 would oscillate even without L2 and C1. However, in this case one would have nothing more than a beat frequency operation (BFO) detector.


    Coil L2 is added to bring the induction balance principle into operation, thus modifying the signal which is returned to the output, and greatly boosting performance.


    This does not mean, however, that we are dealing strictly with an IB detector type, since the design requires a beat frequency oscillator for detection. Also, unlike IB, its Rx section (L2) is active rather than passive, being an integral part of a TCO. Nor is this strictly a BFO type, since its performance far outstrips that of BFO, and of course it uses two coils.


    Search oscillator IC1 oscillates at around 500kHz, depending on the positioning of the coils on the search head. The presence of metal induces changes both in the inductance and coupling of the two coils, thereby inducing a shift in oscillator IC1's frequency.


    The output (pin 6) is taken via a screened cable to a Medium Wave radio aerial. A crocodile clip termination would make a convenient connection.


    The two coils are each made of 50 turns 30swg (0.315mm) enamelled copper wire, wound on a 120mm diameter former. Each has a Faraday shield, which is connected to 0V as shown.


    The coils are positioned on the search head to partly overlap one another, in such a way as to find a low tone on the best heterodyne, which should match the performance mentioned above.


    Oscillator IC1 will sustain oscillation no matter which way the coils are orientated - however, orientation significantly affects performance. The correct orientation may be determined experimentally by flipping one of the coils on the search head. Ideally, the coils will finally be potted in polyester resin.


    The CCO Metal Detector's search head offers a wide area of sensitivity, so that it is better suited to sweeping an area than pinpointing a find. As with both BFO and IB, it offers discrimination between ferrous and non-ferrous metals, making it well suited to "treasure hunting".
    Please could you post the whole circuit.
    Also, in what year was this published in Elektor?
    Thanks.

    Comment


    • #3
      re: Scarborough circuit

      Qiaozhi,

      Did a quick search out of curiosity, found that the article appeared in the Elektor Electronics July/August 2005 issue. Also found a "circuit" diagram here:

      http://www.zen22142.zen.co.uk/Circui...gear/ccomd.htm

      ... have not seen the Elektor article, however the description provided earlier matched what was found on the net. The two links satisfied my curiosity, seems similiar to some of the earlier BFO variations.

      Andy



      Comment


      • #4
        Sorry but what I posted is all Tom sent, didn't say what issue of
        Elektor.

        I think it might have power limitations. Maybe better to use the two
        ouput coils to power separate transistor amplifiers for better penetration.
        He said some of his ideas worked better at low power, but detection of
        coin from 5 inches in air isn't that great.

        Qiaozhi:

        Yes they look similar but not the same. One I posted uses but one external
        capacitor. The link you provided shows one coil driving a transistor base
        which has to make that coil very weak, because base/collector transistor
        currents vary by as much as 1:100, i.e. why they're called "amplifiers." In
        other words, L1 could be 100X weaker than L2. Correct me if I'm missing
        something.
        Last edited by germeten; 11-17-2006, 03:16 PM. Reason: forgot to mention...

        Comment


        • #5
          Originally posted by Andy View Post
          Qiaozhi,

          Did a quick search out of curiosity, found that the article appeared in the Elektor Electronics July/August 2005 issue. Also found a "circuit" diagram here:

          http://www.zen22142.zen.co.uk/Circui...gear/ccomd.htm

          ... have not seen the Elektor article, however the description provided earlier matched what was found on the net. The two links satisfied my curiosity, seems similiar to some of the earlier BFO variations.

          Andy


          Thanks Andy,

          I think I've seen that one before somewhere. The sensitivity is increased by the coil arrangement, but essentially it's still a BFO. A modern VLF detector with the same sized coil should still outperform this design, with the added benefits of ground exclusion balance and better discrimination.

          Comment


          • #6
            Here's a link to the TL071CN IC JFET/op-amp:

            http://www.datasheetarchive.com/sear...1CN&sType=part

            I like this circuit because it's S-I-M-P-L-E, but one chip and a capacitor!

            Comment


            • #7
              MODERATOR: Request this entire thread be taken down at request
              of author. (copyright issues); thanks.

              Comment


              • #8
                I think we have an example of ... (how to say it in English) ... BS (?)

                Read the 'interview':

                http://www.zen22142.zen.co.uk/Media/revts_int.htm

                or read wikipedia on metal detectors in future detectors section

                http://en.wikipedia.org/wiki/Metal_detector

                I will quote it here, in case someone (hopefully) get rid of it.

                While these advances push technology to its full potential, new genres of metal detector have made their appearance. BB (Beat Balance) and CCO (Coil Coupled Operation) were unveiled by the electronics press in 2004. Both were invented by electronics writer and designer Thomas Scarborough, and combine unprecedented simplicity with good sensitivity. The following BB design represents the world's simplest self-contained metal detector: Beat Balance Metal Detector
                I think I can guess who wrote it.

                Pathetic.



                proscan

                Comment


                • #9
                  Well I wish the MODERATOR found it pathetic enough to remove the
                  thread. Tom didn't tell me the info he sent me, and that I posted,
                  was/is copyrighted by Elektor magazine, until after the fact. Just tryin'
                  to keep my tits out of the wringer. Can someone please tell me who
                  the moderator is and how to reach him? I couldn't find a contact link
                  on this whole website.

                  Comment


                  • #10
                    > who the moderator is

                    - Carl. Carl Moreland. (c)

                    Comment


                    • #11
                      Great. Does he read these threads?

                      Comment


                      • #12
                        Originally posted by germeten View Post
                        MODERATOR: Request this entire thread be taken down at request
                        of author. (copyright issues); thanks.
                        From a previous post it looks like this is already in the public domain, so I wouldn't worry too much. Anyway, you haven't posted the complete design, just a small sketch.

                        Comment


                        • #13
                          The schematic is already on the web, plus posting excerpts from articles is generally allowed under int'l copyright law.

                          - Carl

                          Comment


                          • #14
                            OK, well if Elektor contacts me about infringement, I'll have to insist you
                            take the thread down. thanks.

                            Comment


                            • #15
                              JC1

                              Gentlemen,

                              Recently a friend asked me to build him one of these with and artilcle from a british? magazine I believe.

                              Since I have the parts and the wire I had one together in a day. These type circuits (call them whatever you wish) work by having the omp amps on the verge (edge) of oscillating.
                              almost unstable, then with the introduction of metal it goes over the top so to speak. The sensitivity is determined by how close to oscillating the circuit is. In any kind of sensitive configuration, the circuit is Impractile. But for large objects close up it could be ok.

                              It is simple and easy to construct.

                              But not too exciting.

                              Comment

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