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PI metal detector with energy recuperation

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  • PI metal detector with energy recuperation

    Hi all !

    2 years ago I decided to make my own PI metal detector . For the first time I made some experiments with well known PI technology , but one day a very beautiful idea came to me - I found a way how to store and recuperate the energy that we usually waste in the resistor connected in parallel to the sensor coil . I tried this idea and found that it really works . So we can either decrease power consumption of the device or radically increase the pulse energy with the same current from the battery . And after some research I made the prototype , it shows quite a little energy consumption and some other interesting features . Now I decided to publish the circuit of this device - maybe you find it interesting ... But how can I attach the pictures ?

    Best regards
    Dmitry

  • #2
    You can upload attachments after your first posting. So now give it a try.

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    • #3
      ..
      Attached Files

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      • #4
        Originally posted by Carl-NC View Post
        You can upload attachments after your first posting. So now give it a try.
        OK , I'll try now ....

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        • #5
          I tried , but it's still don't work - "You may not post attachments" in the posting rules ...

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          • #6
            You were too fast for the system... it updates every hour, so your promotion to regular "member" had not happened yet. Try now.

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            • #7
              Thanks , now it works OK .
              So here is the circuit :
              Attached Files

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              • #8
                What a coincidence!? Sinclairuser will be very happy with this one!

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                • #9
                  As you can see , the first idea was not to stop the coil current , but to reverse it , using the LC resonant circuit . The first step is to charge the coil ( phase A-B on the time diagram ) , then we have a flyback ( phase B-C ) and current reverse ( just like TV deflection works ) , and after this - the coil voltage drops to the ground and the coil current begins to recuperate . But the metal response begins just after the flyback , and at this moment we have a rapidly decreasing current in the coil , so it will be a great problem to select our signal .

                  So I deciced to use a trick - just after the flyback I open the mosfet switch , and let the current circulate in the shorter chain ( coil , mosfet , diode ) . Now I'm wait for about 100 uS - phase C-D on the right diagram ( and receive the metal response ) , and after it - shut down the mosfet switch , allowing the current to flow back to the power supply . In another words - we use the current , and then return it

                  In order to get the signal from the coil I use the current transformer TR2 ( on the power chain circuit ) . Its output current goes both to tilt compensation circuit and to processing board . Compensation must be used due to losses in the coil chain , so without the compensation we'll have a current decay that will be mixing with the received signal .

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                  • #10
                    You attracted my full attention with this one!
                    But i don't understand much of this?!
                    I am too slow lately, will need couple weeks to analyze all the details!
                    Would help much if you explain details on those transformers.
                    Anyway, even if i don't understand it quite well: it looks very interesting!
                    Any additional photos of device? Videos? Tests?

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                    • #11
                      So , for example , if we have coil current 2 A , and coil wire resistance 0,2 Ohm - we'll have 0,6 V voltage drop , plus about 1,2 V forvard drop on the high-voltage diode ... so we need to apply 1,8 V into the coil chain in order to compensate the loss . And if we do that - the coil current ( without the metals near the coil ) will be constant during all the measuring interval . But the losses in the coil chain depends on temperature , so I use another trick - I let the current after my current transformer TR2 flow through 2 little diodes ( 1N4148 ) and one copper resistor .... the idea is that this network will behave itself when temperature is changing just like the main sensor coil chain does , and if I amplify this voltage and apply it to the coil chain in right polarity ( through the TR3 transformer ) - I will completely eliminate the temperature effect .

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                      • #12
                        Originally posted by ivconic View Post
                        You attracted my full attention with this one!
                        But i don't understand much of this?!
                        I am too slow lately, will need couple weeks to analyze all the details!
                        Would help much if you explain details on those transformers.
                        Anyway, even if i don't understand it quite well: it looks very interesting!
                        Any additional photos of device? Videos? Tests?
                        Of course , if I publish it - now I need to explain all the things Please excuse me for this complexity , but I really couldn't make it simpler ... and initial idea seemed so beautiful to me , that I decided to pass it through anyhow . And I did it - now it works . Here are the photos :
                        Attached Files

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                        • #13
                          wow,

                          that's art work!!

                          nice job on the construction !!

                          Philip

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                          • #14
                            I cannot believe, so complex circuit and only one control. Seems author of LTC64 with 13 control (13! for God's sake!) need here a lot to learn.

                            Congratulation deemon, that you even put so complex apparatus to work.

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                            • #15
                              Hello Dimitry,
                              You blow my mind , very good work and too much for me , i see a nice engineering like the use in space program ...
                              i congratulate for your effort and result ....i realize i am far from your electronics knowledge...it is good to feel in i will try to analyze section to section for my understanding ...thank you for your work
                              Alexis

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