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  • #91
    Originally posted by pelanj View Post
    This project is of a high interest for me and if my knowledge permits, I will try to contribute my part. My field of focus is searching for (small) silver coins in ploughed and rolled fields and pastures. The coin diameters are starting at 10 mm. There is a lot of iron in the fields, so iron discrimination and either fast recovery or non-motion principle for unmasking the non-ferrous target is necessary. My secondary interest is hunting for coins and jewellery in the sand at the Baltic sea beaches. So far I have used VLF and FBS detectors and a military PI by Ebinger on the beaches. I dig targets (2.5 cm coin) from about 12-13" maximum with the detectors I have. I would really like to go deeper in the sand. In the dirt, I would like to get precise iron discrimination for coin sized objects to at least 12", to go deeper than conventional VLF detectors. If there was an option to use large coil for locating large deep objects, it would be great as well.

    What I could help with? Unfortunately not much, but I have done some single chip and PLC programming and have a possibility to use MATLAB/Simulink for code generation (unfortunately not Embedded, but standard C/C++).
    Hi pelanj,

    your knowledge of programming is just what we need.
    If you can help writing some code for the PIC16F690 that I am using, it will be of great help.

    How did the Ebinger perform on the beach?

    All the best

    Tinkerer

    Comment


    • #92
      I have never really worked with PIC, but some ST7 and ATMEL. All the development tools stayed at my previous job, but I will order a PICkit 2 Starter Kit so that I get my own programmer. It should not be too different from ST7/Atmel programming.

      The Ebinger is quite OK - it is an EB420 and is for sale on e-bay time to time. It is quite sensitive and I dug 1 DKK out of sand from the same depth as with a Minelab Quattro with the 15x12 SEF DD coil - cca 30 cm/12" It might have been good luck as since then I have had only average 20-25 cm deep finds. The worst part to the EB420 is that it is sensitive to ground sometimes - and at the beach where I hunt the ground response varies quite a lot. Maybe it is small pieces of iron/rust, I do not know. On the other hand, it is really sensitive to small pieces of metal, sometimes I had trouble to see what I have found - tiny wires from fishermen (some kind of steel) very thin and some 5-10 mm long.

      I would really like to have a very stable detector as it is tiring after while with the EB.

      Comment


      • #93
        Originally posted by pelanj View Post
        I have never really worked with PIC, but some ST7 and ATMEL. All the development tools stayed at my previous job, but I will order a PICkit 2 Starter Kit so that I get my own programmer. It should not be too different from ST7/Atmel programming.

        The Ebinger is quite OK - it is an EB420 and is for sale on e-bay time to time. It is quite sensitive and I dug 1 DKK out of sand from the same depth as with a Minelab Quattro with the 15x12 SEF DD coil - cca 30 cm/12" It might have been good luck as since then I have had only average 20-25 cm deep finds. The worst part to the EB420 is that it is sensitive to ground sometimes - and at the beach where I hunt the ground response varies quite a lot. Maybe it is small pieces of iron/rust, I do not know. On the other hand, it is really sensitive to small pieces of metal, sometimes I had trouble to see what I have found - tiny wires from fishermen (some kind of steel) very thin and some 5-10 mm long.

        I would really like to have a very stable detector as it is tiring after while with the EB.
        I would like to identify the problems you have with the EB, so that we can avoid them with our design.
        Is the EB a motion machine or is it a static machine?

        Does it have ground balance? How do you tune it for the salty sand beach?

        Does it have a fast response?

        How is the audio? VCO? single frequency with increase of volume for target?

        How do you set the audio? Very low volume? Low frequency? What frequency?

        Tinkerer

        Comment


        • #94
          It is a motion machine, however the sweep speed can be really low. There is no ground balance on this model, the only knob sets the sensitivity. I usually set it to a low threshold sound and with a moderate sweep speed try to listen for fast changes in audio, the slow random changes are the ground. The response is not what I would call fast - with a fast sweep it does not react fast, but with medium and low speed it responds very precisely. This is not a problem, it just takes time to adjust to it, I am used to Tesoro lightning speed response

          The audio is VCO, with the presence of target both loudness and pitch increase. I like that, however due to instabitily, the changes are perceptible even without a target, which does not allow hunting for "whispers" in the threshold. Except from this audio, there is a clicking sound, but it indicates battery voltage and not target.

          I have never used any other PI, but I like the way the clicking works - it is quite easy to hear a change if the basic pace is around 1 Hz. Then,if the signal is really strong, a VCO like signal works the best for me. I have recently got a Tesoro Sand Shark - and I kind of like its audio - no clicking, but very recognisable changes in threshold in VCO mode. I also kind of like a feature of the Minelabs - if it is iron, there is a silence in the threshold tone.

          One important question to this new design rises - what would be the masking/unmasking possibilities with discrimination? I mean - would a coin be detected next to a similar sized piece of iron or would it be "hidden" by it? Or would it be possible to let the iron "spit" and have the good target a smooth response for the good ones similar to VLF (esp. Tesoro detectors, which I am used to).

          Comment


          • #95
            Originally posted by pelanj View Post
            It is a motion machine, however the sweep speed can be really low. There is no ground balance on this model, the only knob sets the sensitivity. I usually set it to a low threshold sound and with a moderate sweep speed try to listen for fast changes in audio, the slow random changes are the ground. The response is not what I would call fast - with a fast sweep it does not react fast, but with medium and low speed it responds very precisely. This is not a problem, it just takes time to adjust to it, I am used to Tesoro lightning speed response

            The audio is VCO, with the presence of target both loudness and pitch increase. I like that, however due to instabitily, the changes are perceptible even without a target, which does not allow hunting for "whispers" in the threshold. Except from this audio, there is a clicking sound, but it indicates battery voltage and not target.

            I have never used any other PI, but I like the way the clicking works - it is quite easy to hear a change if the basic pace is around 1 Hz. Then,if the signal is really strong, a VCO like signal works the best for me. I have recently got a Tesoro Sand Shark - and I kind of like its audio - no clicking, but very recognisable changes in threshold in VCO mode. I also kind of like a feature of the Minelabs - if it is iron, there is a silence in the threshold tone.

            One important question to this new design rises - what would be the masking/unmasking possibilities with discrimination? I mean - would a coin be detected next to a similar sized piece of iron or would it be "hidden" by it? Or would it be possible to let the iron "spit" and have the good target a smooth response for the good ones similar to VLF (esp. Tesoro detectors, which I am used to).
            I agree with you, that a good audio can help a lot to make a good detector. So let's start with that part of it.

            The TEM_TINKERER_IB-PI gives a positive response for non-magnetic targets and a negative response for magnetic targets. Therefore we can process the responses separately and give each it's on audio output. I have not developed that yet but with your help we may get it done.
            This detector is not very sensitive to iron, but very deep and sensitive to non magnetic targets.

            We also want a fast response for a motion machine. A non motion machine can use a slow response, but each type of machine needs to be swept at a sweep speed according to it's filters for best results.

            A fast response means that the audio must not lag more than 10 to 30ms, depending on coil diameter, behind the target. A slow clicking sound can not manage that.

            I am using the PIC16F690 at present. I have it setup for 4 different timing schedules and 8 different TX Taus. 4 different RX Samples. I suggest we start with that and when we find we need more processing power, we change to a different PIC.

            Tinkerer

            Comment


            • #96
              From my point of view, there are a few variants how to make the audio.

              1. Standard threshold based sound. Iron would make a low sound and amplitude would be dependend on the brake signal. The non-iron targets would make a high pitched sound with an option of VCO.

              2. Silent mode - iron makes low sound, non-iron would make a high sound. Both would have separate volume (like a C.Scope CS6MXi), so that the iron volume can be set to a low volume just to inform about iron in the ground.

              We need to make sure that good targets do not show up in the iron range under any condition. My development kit is on the way - it should arrive within next week.

              Comment


              • #97
                An interesting balanced coil idea: http://www.hq-elektronic.eu/data/patent_z_jarch.pdf
                It is in Czech, but look at the pictures at the end of the document.

                Comment


                • #98
                  Originally posted by pelanj View Post
                  An interesting balanced coil idea: http://www.hq-elektronic.eu/data/patent_z_jarch.pdf
                  It is in Czech, but look at the pictures at the end of the document.
                  Very interesting coil arrangement. Let's see if I can translate the text.

                  Thanks

                  Tinkerer

                  Comment


                  • #99
                    I was quite surprised that google translate makes a quite readable translation. If you have any specific question, I can help with understanding.

                    Comment


                    • Originally posted by pelanj View Post
                      I was quite surprised that google translate makes a quite readable translation. If you have any specific question, I can help with understanding.
                      The translation is good enough for somebody familiar with IB coils to understand. I guess, the only way to see if there is an advantage over the concentric co-planar IB coils, is to build one of each of the same diameter and inductance and try them out.

                      Tinkerer

                      Comment


                      • OK, the programmer and small 16F690 board is at home. So it is time to think how to make the audio. What inputs will there to code the audio from?

                        I would use one of the PWM outputs to drive a FET to make a "class D" audio amplifier, if that is OK. Two tone audio - low tone for iron with volume modulation and high tone for non ferrous with volume and frequency modulation. The resulting mix would be a matter of a simple calculation and then it would be sent to the PWM output. I guess some averaging/filtering will be needed to tame the response a little. I think it could be used without a threshold tone, but it is possible to have it if needed.

                        I would maybe also include a selectable "mono tone", that is beep for nonferrous, silence for ferrous. Either with threshold or without.

                        Comment


                        • Originally posted by pelanj View Post
                          OK, the programmer and small 16F690 board is at home. So it is time to think how to make the audio. What inputs will there to code the audio from?

                          I would use one of the PWM outputs to drive a FET to make a "class D" audio amplifier, if that is OK. Two tone audio - low tone for iron with volume modulation and high tone for non ferrous with volume and frequency modulation. The resulting mix would be a matter of a simple calculation and then it would be sent to the PWM output. I guess some averaging/filtering will be needed to tame the response a little. I think it could be used without a threshold tone, but it is possible to have it if needed.

                          I would maybe also include a selectable "mono tone", that is beep for nonferrous, silence for ferrous. Either with threshold or without.
                          Excellent.

                          I like your suggestion of the 2 tone audio. Please PM me with your email address, so I can send you the source code .asm file of the existing timing schedule.
                          Then we can see what changes we need to make in the use of the output pins.

                          Tinkerer

                          Comment


                          • Almost orthogonal coil configuration

                            I am slowly progressing in learning the PIC language. I hope to come up with more soon, I plan to create tone generating code and test it first.

                            Anyway, I was thinking if the detector could be used with the almost orthogonal coil configuration, aka "2box detector". Then, would it still discriminate large iron against large non-ferrous targets to say 1m depth? I am really intrigued to try a "hoard searcher", but with a useful discrimination. Would it find also shallow coind sized object?

                            Comment


                            • Originally posted by pelanj View Post
                              I am slowly progressing in learning the PIC language. I hope to come up with more soon, I plan to create tone generating code and test it first.

                              Anyway, I was thinking if the detector could be used with the almost orthogonal coil configuration, aka "2box detector". Then, would it still discriminate large iron against large non-ferrous targets to say 1m depth? I am really intrigued to try a "hoard searcher", but with a useful discrimination. Would it find also shallow coind sized object?
                              I don't think that a traditional 2 box detector is capable of finding coin sized objects, but I have no personal experience with such detectors.

                              The way I see it, the target size corresponds mostly to the field strength, or we could say, the amount of field lines that the target intercepts.

                              With the almost orthogonal coil arrangement, the field inciding on the target is only a fraction of the total TX coil field. Therefore it needs a fairly large target to generate sufficient response.

                              It seems that 2box technology has been lagging a bit behind the general metal detector development, but I suspect that great improvements can probably be made.

                              Useful iron discrimination should be possible, but a treasure inside an iron box will only be detected as iron.

                              Tinkerer

                              Comment


                              • I have heard from a TM808 user that when you tilt the front coil closer to the ground, it would react on small objects to some 10 cm depth. Which is what the hoard hunters usualy do not want.

                                You are right about the iron box, but usually you find silver coins in either leather pouches or ceramic pots here. Not that I have found one myslelf, but I have seen a few reports of these finds.

                                Comment

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