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Project: Goldfish

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  • Project: Goldfish

    I've decided to build a simple shallow water metal detector. There are a few freshwater beaches where I live that need searching. I've used land-based detectors on a float years ago, but why not make a water-proof one. I've adapted the basic Bandido circuitry for this. I eliminated the non-motion pinpoint mode. All I need is a good motion discriminator with decent depth. I don't have a lot of room in my enclosure so it's good this circuit will work with only one 9V battery.
    The enclosure I chose is from a nearby sporting goods store. It's a small bright orange (goldfish colored) water-proof storage container. I plan on mounting all controls directly on the PCB so there will only be a need for 2 holes in the case; one for the coil cable and one for the headset. I have watertight strain reliefs for those two. Also, I have some small T-nuts that I will glue or caulk to the bottom of the case. This will give me something to mount the PCB to without drilling any holes.
    The sensitivity and discrimination pots will mount where the 2 circles are marked on PCB. I won't be able to adjust discrimination once I'm in the water, but I find I don't seem to ever do that anyway. I run with very low disc because of thin gold rings and just scoop up everything. I eliminated the threshold control and made the ground balance a PCB mounted trimmer.
    The layout is nearly complete. As you can see, even the 9V battery will mount on the PCB. I have some nylon strap that I will loop though the loops on the top and bottom of the case so I can wear it across my chest and wade with it.
    Here is a picture of the case and a 3D rendering of the PCB. I'll post more as I progress. I hope to finish by September because that's when many of the local beaches close to swimmers and metal detecting is allowed.

    Merc
    Attached Files

  • #2
    much succes merc
    looks good

    have you place for a second 9v batterie in parallel (last longer)

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    • #3
      I don't think I can fit a second battery. I don't believe it is needed as the circuit uses very little current with headphones. I like the simplicity of the Bandido circuit.

      Merc

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      • #4
        Goldfish Update

        Well, it's time to get back on this project. I have most of the ICs. Just need a few caps and resistors. I got the PCB mounted 9V battery holder in. You can see it on the printing of the PCB layout. I have the water-proof connectors mounted. Getting the holes drilled where I needed them was harder than I expected. I destroyed the first box. This one is my second attempt.
        Attached Files

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        • #5
          This is very interesting. I might go for something like this as well. Frankly, I've never seen a box so well designed and now I know what to seek.

          I learned some time ago that drilling holes in difficult materials often works better if you do it against the rules. Hard plastic as well as oak are best drilled with drill bits as blunt as possible, and at highest speed there is, applying only a light pressure. What happens is that drill bitt's tip gets very hot and goes through very neatly. In fact it is the only way to make a nice hole in oak without ragged exit hole. As a bonus the oak becomes charred, and it is a good thing because of oak's natural alkalinity - charring makes it less corrosive.

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          • #6
            Here is the picture of how I am mounting the PCB in the enclosure. Simply using T-nuts with a touch of caulk. I then placed the PCB down and let the T-nuts find their proper location. After the caulk firms up a little, I will probably remove the PCB and add a small amount more to each one.
            Attached Files

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            • #7
              Nice work Merc.

              I also mill my pcb's or have them made. No more chemicals. It took a few years to perfect, but now its pretty quick.

              Drilling plastic is easy with a step bit or "Unibit". The best ones are made by Irwin, but expensive. More affordable from Harbor Freight. They also work good on aluminum. Always drill a small lead hole first.
              http://www.harborfreight.com/3-piece...lls-91616.html

              Keep us posted on your progress.

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              • #8
                Assembly has begun. I've already hit some problems. My sensitivity pot is also the power on/off switch. Because of the added switch, it's thicker than I expected so I will probably have to use spacers to stand the board away from the bottom of the box.

                Merc
                Attached Files

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                • #9
                  I thought of using a reed relay and a magnet for switching things in some enclosure.

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                  • #10
                    I have the PCB totally assembled with all components. I have made a video of my testing of the assembled board. I have an external speaker attached for testing. I am building a set of headphones for it and awaiting the arrival of a 10" DD coil.

                    Here is a link to the video:
                    http://www.youtube.com/watch?v=C3s4_wQQA5M

                    Merc

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                    • #11
                      Nice, who makes the box? Where did you buy it?

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                      • #12
                        I bought the box at a local store called Sportsman's Warehouse. I belive it's called a Gearbox. Hear is a link to an online store that has them.

                        http://www.summitcampinggear.com/gsi...cotorange.html


                        Just search for GSI Gearbox 1 Apricot and it will come up. They make other slighly large boxes as well. It's meant to keep food and other items dry while camping.

                        Merc

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                        • #13
                          Thanks, did a bit of extra searching and found some more boxes:
                          http://thewaterproofcasecompany.com/...tegory_Code=S3

                          http://thewaterproofcasecompany.com/...tegory_Code=S3

                          This site has many more boxes as well.


                          As for drilling holes in plastic, standard drill bits chip, melt the plastic as it drills. I have been using special drill bits made for plastics since 1980 that make perfect holes. Take a look here:
                          http://www.rplastics.com/plasticdrill.html

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                          • #14
                            hello merc

                            would you please be so friendly and give pcb files here
                            please

                            i´m not sure which project i should do next
                            also have your bandido pcb here , silver sabre plus and aztec

                            but the goldfisch looks very nice small pcb for 9V

                            i think it would be better one to try

                            regards

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                            • #15
                              See if this will suffice.

                              Merc
                              Attached Files

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