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Fishing Black Box

Discussion in 'General Electronics Discussion' started by rhaugen, Feb 23, 2014.

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  1. rhaugen


    Feb 21, 2014
    Hello everyone. I am starting a project and am looking for advice/guidance/suggestions. Here is the scenario: It has been well documented that certain species of fish are attracted to a specific electrical charge around a boat. Of course the other end of this is that they are repelled if the voltage is not set/adjusted right. There are several commercial versions of what is called a "black box" that are worth about $200 - $300. The principal is pretty simple so I have been investigating how to fabricate my own.

    So to start with the electrical system in the boat is of course grounded through the inboard engine. However the inboard engine block is electrically connected to the metal leg of the boat that is sitting in , in my case, salt water. So that is the negative side of the potential. The positive side will be metal downrigger cables that will be in the salt water. Apparently there is a "natural" potential occurring between the downrigger cable and the leg of the motor that has to be taken into account. The downriggers that I will be using are electric so they are driven by the 12v battery/alternator in the boat. As I have not installed the downriggers yet I cannot tell you what sort of potential reading I will get between the engine ground and the downrigger wire but the electrical motor is isolated from the downrigger cable.

    What I need to do is built the electronics to be able to adjust this "natural" voltage to a prescribed amount. I should mention that the electric contact with the downrigger cable is just a couple of turns of wire through which the cable goes and touches them. This is attached to the downrigger booms.

    The "ideal" setting would be somewhere between .25 V to 1 V DC. The commercial system runs off a 9v battery and their specifications indicate a maximum current of 0.1 A so we are not dealing with any large potentials.

    The system should be able to do a couple of things:
    1) Use either an installed 9v battery or allow hook up directly to 12V system of the motor.
    2) Measure and display the current "natural" voltage (ie just measure the potential across engine ground and the downrigger cable
    3) Impart or reduce this natural voltage to a set amount in the range of 0.25V to 1.0V DC

    And finally I would like to use a small 3 digit LCD for the display.

    Sorry this became so wordy but I am hoping that by explaining it well, will help those who would be willing to wade in.

    Thanks in advance for any and all help.

  2. rhaugen


    Feb 21, 2014
    Thought I would ask if anyone is interested in helping me out as I have not received any responses. Being a newbie perhaps I started this in the wrong thread.

    Regards all
  3. davenn

    davenn Moderator

    Sep 5, 2009
    hi ya Ray

    sorry I cant help you ... never heard of fish being attracted by electrical charges in the water
    and due to the lack of responses from others... Im assuming they haven't either

    Unless you were able to supply more specific info on how these other "black Boxes " worked, there's probably not much anyone could suggest as a starting point

    just my thoughts

  4. rhaugen


    Feb 21, 2014
    Dave, thanks for providing some feedback. Perhaps I was too detailed in my explanation. If that is possible. I did find a schematic that I got off another site and have built this one. It does put out a variable voltage. I did have to change the feedback resistor of the op amp to get it down to the range that I was interested in.

    Then the question I came up against is " How would you compensate if the voltage reading from the downrigger is higher than you desire ? Would you need to add a negative voltage ?

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