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  • Originally posted by Tinkerer View Post
    The pictures are only meant to show the wave shape. For example, the current picture shows a 12A pulse, while the TINKERERS_SB uses only 4A.

    I have a HEX file ready, I just want to test run it first before posting.

    The Mosfet driver expects a pulse that is ON for about 97us and OFF for 7us, for a total cycle of 104us or about 10k PRR. This is when using a 300uH coil and a 4.7nF capacitor.
    You should then get a Flyback of about 550V.

    This is the INVERSE of a traditional PI, where the TX is ON for a short time and OFF for a long time.

    If you use a traditional PI pulse timing, the coil will ring and the Mosfet will get hot and might self destroy.

    Tinkerer

    Either I'm getting too tired or I'm missing something here.

    My understanding is a standard PI would be FET on for say 100us then off again for say 300us then back on again.

    Whereas my understanding which is opposite to what your saying is that the FET in the TEM should switch on for 7us then switch off for 97us.

    Or am I getting really mixed up.


    Cheers
    Mick

    Comment


    • Originally posted by mickstv View Post
      Either I'm getting too tired or I'm missing something here.

      My understanding is a standard PI would be FET on for say 100us then off again for say 300us then back on again.

      Whereas my understanding which is opposite to what your saying is that the FET in the TEM should switch on for 7us then switch off for 97us.

      Or am I getting really mixed up.


      Cheers
      Mick
      You understand right. The TX is ON for 97us and OFF for 7us. That means it is ON almost all the time.
      This is a totally new and different Pulse Induction technology. It uses a high power TX pulse while consuming little power out of the battery, due to it's resonant component.

      Tinkerer

      Comment


      • Originally posted by Tinkerer View Post
        You understand right. The TX is ON for 97us and OFF for 7us. That means it is ON almost all the time.
        This is a totally new and different Pulse Induction technology. It uses a high power TX pulse while consuming little power out of the battery, due to it's resonant component.

        Tinkerer


        Thanks Tinkerer, I'll change my timing tomorrow and have another go.

        I think R1 on the TX schematic is incorrect, I would have thought that it would be connecting to ground, like in some of your earlier schematics.



        Cheers
        Mick

        Comment


        • Originally posted by mickstv View Post
          Either I'm getting too tired or I'm missing something here.

          My understanding is a standard PI would be FET on for say 100us then off again for say 300us then back on again.

          Whereas my understanding which is opposite to what your saying is that the FET in the TEM should switch on for 7us then switch off for 97us.

          Or am I getting really mixed up.


          Cheers
          Mick
          You should play with Aziz's simulation Mick. Not sure exactly where it is anymore... Anyway here's a picture of what the mosfet gate is doing with respect to coil current:
          Attached Files

          Comment


          • Originally posted by mickstv View Post
            Thanks Tinkerer, I'll change my timing tomorrow and have another go.

            I think R1 on the TX schematic is incorrect, I would have thought that it would be connecting to ground, like in some of your earlier schematics.



            Cheers
            Mick
            Thanks for the observation. You are correct, R1 should go to 0V or can be omitted.

            Tinkerer

            Comment


            • Actually it is more of a step voltage than a TEM, but does the same job, and step is more PI like. Call it as you wish, but we have finally something new on the block.

              My suggestions would be to reconsider the level of filtration throughout system. You have incredible number of filtering stages, and you know about "too much of the good stuff". For starters I'd remove C33 because of the changing impedance of that particular circuit. Then I'd continue removing R14, C26 and R45 (offset is fixed elsewhere already).

              My focus recently is on the differential inputs, such as yours. Nice job

              Comment


              • Originally posted by Davor View Post
                Actually it is more of a step voltage than a TEM, but does the same job, and step is more PI like. Call it as you wish, but we have finally something new on the block.

                My suggestions would be to reconsider the level of filtration throughout system. You have incredible number of filtering stages, and you know about "too much of the good stuff". For starters I'd remove C33 because of the changing impedance of that particular circuit. Then I'd continue removing R14, C26 and R45 (offset is fixed elsewhere already).

                My focus recently is on the differential inputs, such as yours. Nice job
                Davor, thanks for the feedback.

                I agree on C33, C26, R14, R45. It will work without that. The reasoning is to use always the minimum bandwidth needed.

                Will it make a difference? Only trying we will really know.

                Tinkerer

                Comment


                • Noise-wise C18/C38, the first filtering stage plus a differenting integrator make sense, and more than that is just overkill, and will introduce some serious delays.

                  Audio stage can be improved by introducing some proportionality to volume. OK, you have proportional frequency, but in absence of targets you could enjoy some privacy
                  How about a simple twin T at the audio output, say, in series with R4?

                  Comment


                  • Originally posted by Davor View Post
                    Noise-wise C18/C38, the first filtering stage plus a differenting integrator make sense, and more than that is just overkill, and will introduce some serious delays.
                    Audio stage can be improved by introducing some proportionality to volume. OK, you have proportional frequency, but in absence of targets you could enjoy some privacy
                    How about a simple twin T at the audio output, say, in series with R4?
                    Thanks for the feedback.

                    About the noise filters: Inside the house, the open breadboard picks up the 60Hz noise on every wire lead. The filters really help there.
                    Inside a shielded box this would be different and some of the filters will become redundant.

                    However, one keeps hearing about detectors that are much affected by mains noise, so I really don't know. It needs testing of the final product.

                    The audio. I can say it works, but it is not where I want it yet.
                    As is, the target signal needs to be about 50mV or more to be discerned. I would like it to be about 10mV.

                    The differentiation between FE and gold is easy to hear.

                    The flexibility of the floating "center" frequency is nice too. It gives some leeway for the ground variation.

                    The continuous tone is annoying. A tween T filter at the center frequency would help for that. Adding a target volume response would help a lot.

                    I think pelanj is working on that.

                    The speaker has a resonant frequency where it is louder.

                    The square wave makes a horrible sound. The problem of a filter, to take the edges off, is the variation of the frequency from 50 to 1000Hz. Of course it can be filtered, but it gets quite involved and the idea of this specific circuit is to keep it extremely simple.

                    Tinkerer

                    Comment


                    • Yes I see, so you actually wish audio to accent the small variation at ~10mV and at the same time you wish to maintain the convenience of the non-motion detector, and you are happy with some floating, yet the circuitry around U3a suggests otherwise.
                      Considering U3a being configured as a non inverting amp, with minimum gain being 1, and the feedback resistor R20 being nailed down to the ground, also being configured as a log amp IF input signal is referenced properly to the ground, you are actually quite close to your perfect audio. In case you do not oppose to turn U3a into a perfect PD controller, you could connect the R20 to a large grounded capacitor or a slow servo, and voila, your audio will gain a more edgy response for targets, and retain the proportional response for the baseline. You might want to pump up some gain in the preceding stages though, because without the target kick, it will revert to the unity gain.

                      BTW, the 50Hz problem is more of an input stage problem. Point is that input coil will pick 50Hz either as a differential signal by magnetic flux, or more likely capacitively as common mode signal. If it hits the switchers you'll have some nasty interference. Your input is a real differential one and it takes care of the common mode quite efficiently, but you might consider some differential mode highpass filtering - just in case.
                      Shortly, you'll fight 50Hz more efficiently with single HPF at the preamp than with heavy LPF further on.

                      Comment


                      • all major pi fails for the audio circuit, we say that 3 o 4 years ago in the forum , we put a lot of efforts in the front end etc...circuits ..... but a very poor design audio , 50 mV too much ...first use a correct VCO you need a specialized circuit like a ad 654 and mix it with the treshold audio classic ....it is the best for me for audio....

                        Comment


                        • Hi Tinkerer, I believe I've fixed the problem. Like you said the timing is opposite to normal PI. ATM I'm running the circuit with just a standard Mono coil from one of my other circuits and another mono roughly configured to induction balance and I can see definite changes depending on target type.

                          Next is to build a better coil.

                          I'm impressed......


                          Comment


                          • Micks Target shot's

                            Hi All. I thought I had better show some of my target shots. These shots are taken from a second coil in a rough DD setup. The receive coil is only mono loop at the moment, for experimenting. and the cro shots are directly from the coil with no amp.

                            Nails and bolts show next to no response or if they do the cro shows a lower response.

                            I should also mention I had to change the 4.7nf cap to a 10nf cap to get the 7us pulse, I guess this is for the coil size I'm using.


                            Also my sub gram nugget measures a positive response, whilst a red house brick shows a negative response.



                            No Target




                            Lead Target




                            Steel Target

                            Comment


                            • Hey Mick,

                              now show us the "masking effect" of the targets. Make three measurements:
                              1. Gold nugget alone
                              2. Hotrock alone
                              3. Gold + Hotrock together.

                              Cheers,
                              Aziz

                              Comment


                              • Originally posted by Aziz View Post
                                Hey Mick,

                                now show us the "masking effect" of the targets. Make three measurements:
                                1. Gold nugget alone
                                2. Hotrock alone
                                3. Gold + Hotrock together.

                                Cheers,
                                Aziz
                                Well you had better send me some hotrock's then.

                                Comment

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