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Building the Geotech Barracuda Rev A (from silverdog)

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  • #31
    By now just set aside about the damping resistor. Any damoing between 270R-500R damping can easily give you atleast 6" on coins.. just refined the damping after you manage it to detect that depth.

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    • #32
      Originally posted by ionut_mtb View Post
      make a picture of your coil and post here, i want to see also the wire you use. i think 20 turn is less than what you need, maybe your uH metter not showing good. you can play more with the delay. for now i don't have power potentiometer to find the best value for dumping resistor, but i bought few resistors 200, 240,280....400, 440 ohm and i just test to see best result.
      Hi, a picture of the coil wouldn't be of much use because is wrapped on electrical tape, then cable organizer, and then electrical tape again, so it looks like a big taped circle, just that. I used 0.4mm insulated copper wire, Qiaozhi told me to give it 20 turns on a 10" diameter. My lcr meter is accurate, is a DER EE DE-5000, if you want to check it out, there are many reviews done buy people like Dave on the EEVBLOG (if you don't know him check out his youtube channel!) So I trust the meter, I don't think is giving me a wrong value. But how many turns would you suggest? Thanks

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      • #33
        Originally posted by jladre View Post
        Azigta you are very near to finish it. Just adjust your delay trimmer until it hardly pick up the magnet and pick a decent depth on coins. Wave a coin under the coil while adjusting the delay.
        I will do that today and see what the delay trimmer does. Yesterday I was doing tests changing the delay trimmer and the sample delay pot and I couldn't notice any difference. Today I will run more tests, puting metallic things away and so.

        The magnet is a small neodimium magnet, which seems to be a very powerful magnet, maybe I should try with other magnet? I don't think I can manage to adjust the meter not to detect this powerful magnet. Is not big but it sticks to coins very hard xD

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        • #34
          I have tested everything I could. The min delay trimmer doesn't seem to do anything at all, same for the delay pot. It doesn't affect the detection depth. What could be wrong?

          Maybe is because I didn't adjust the minium delay trim properly, Is there any way I can adjust this ? I can't reach that -2.1v on u7 pin 1 by any means. Maybe this is the problem. Or maybe the coil isn't enough? No idea...

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          • #35
            original coil should have 450uH and 1R5 to mach exactly the original the damping resistor 330R. Of course 300uh should work also. do you have a shield on the coil? if is not correct shielded you cand get poor performance. first try without shield. the trimmer for min delay have like 25turns so you have to check where is the best performance of detection.
            you need to use this circuit to find best dumping value.Click image for larger version

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            • #36
              Originally posted by ionut_mtb View Post
              original coil should have 450uH and 1R5 to mach exactly the original the damping resistor 330R. Of course 300uh should work also. do you have a shield on the coil? if is not correct shielded you cand get poor performance. first try without shield. the trimmer for min delay have like 25turns so you have to check where is the best performance of detection.
              you need to use this circuit to find best dumping value.[ATTACH]38995[/ATTACH]
              I do have a shield in the coil, maybe is a poor shield but I have it xD It's made from aluminum foil, I will unwrap the coil and see what results do I get without the foil, maybe the next time I shield it I will shield it with sticky copper tape, I couldn't find in my city, but I'll buy it from ebay. I think I will buy some 2w resistors starting from about 200ohm and try it. Is it dangerous to put a too low resistor there? I will post here the results without the shielding soon.

              edit: Without the shield it measures 288uH. I think I will add more turns to it.

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              • #37
                Originally posted by azigta View Post
                I do have a shield in the coil, maybe is a poor shield but I have it xD It's made from aluminum foil, I will unwrap the coil and see what results do I get without the foil, maybe the next time I shield it I will shield it with sticky copper tape, I couldn't find in my city, but I'll buy it from ebay. I think I will buy some 2w resistors starting from about 200ohm and try it. Is it dangerous to put a too low resistor there? I will post here the results without the shielding soon.

                edit: Without the shield it measures 288uH. I think I will add more turns to it.
                Make sure you leave a gap in the shield, otherwise it will act like a shorted turn, and you will get very poor sensitivity.

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                • #38
                  Originally posted by Qiaozhi View Post
                  Make sure you leave a gap in the shield, otherwise it will act like a shorted turn, and you will get very poor sensitivity.
                  Hi, I added more turns and it now measures 470uH, quite a lot more than before, but it's still less than 500uH so It should work. It does work because I've made tests but It's the same as before. I guess that the damping resistor value doesn't work for this value of inductance. Could you tell me what resistor do I need? Or do I buy a power potentiometer and put it there and start testing until the detecting depth is ok? Could that work? xD

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                  • #39
                    Originally posted by azigta View Post
                    Hi, I added more turns and it now measures 470uH, quite a lot more than before, but it's still less than 500uH so It should work. It does work because I've made tests but It's the same as before. I guess that the damping resistor value doesn't work for this value of inductance. Could you tell me what resistor do I need? Or do I buy a power potentiometer and put it there and start testing until the detecting depth is ok? Could that work? xD
                    The coil details I supplied earlier and the damping resistor will work just fine with the Baracuda. I very much doubt that is the problem.

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                    • #40
                      Originally posted by Qiaozhi View Post
                      The coil details I supplied earlier and the damping resistor will work just fine with the Baracuda. I very much doubt that is the problem.
                      Oh, then what could the problem be? Any idea? Maybe it has to do with R14? I couldn't adjust it because I can't get -2.1v on U7 pin 1

                      by the way, with the 288uH coil, I was getting an audible tone from the coil, now with the 470uH coil That tone coming from the coil is barely audible, You have to get your ear close to the coil to hear it. I don't know what this means. But I post it here just in case rings any bell

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                      • #41
                        I tested the diodes again and there are 2 diodes that apparently let the current flow both ways, that isn't what they are supposed to do, right? Maybe there's a problem? This diodes are D1 and D2, 1N4148 diodes. I tested them in circuit with the diode function and they measure 580mv on both ways There are other 1n4148 diodes on the board, like D4 and D5 and they measure 603mV only the way they are supposed to be measured, positive probe on positive side of the diode, negative probe on the negative side. Is this normal? Aren't this diodes supposed to give me an L on the multimeter when I place the positive probe on the negative side of the diode and the negative probe on the positive side of the diode?

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                        • #42
                          Originally posted by azigta View Post
                          I have tested everything I could. The min delay trimmer doesn't seem to do anything at all, same for the delay pot. It doesn't affect the detection depth. What could be wrong?

                          Maybe is because I didn't adjust the minium delay trim properly, Is there any way I can adjust this ? I can't reach that -2.1v on u7 pin 1 by any means. Maybe this is the problem. Or maybe the coil isn't enough? No idea...

                          Hello azigta, I have been following your progress and it sounds like you are close to getting the Barra working properly, but your pcb sounds like it still has some sort of problem, I have repaired a couple of these PCB's for a fellow here in Australia, he did some terrible things to those PCB's, but after spending many many hours on them I managed to get them both working, one was better than the other, these PCB's will tolerate a certain amount of soldering and un soldering before they start doing weird things after the tracks start lifting especially around VIAS, as you have done a lot of soldering and un soldering you probably have a build up of flux residue, have you cleaned the back of the PCB with Methylated spirit the Spanish name seems to be alcohol de quemar,

                          Useing a small tooth brush and some Methylated spirit gently clean the flux residue from the PCB, let it dry, you will probably have some white residue left, clean this off again, let it dry, the flux build up can cause some erogenous signals on the pcb and a clean pcb is a good place to start .
                          You say the delay POT does nothing, if does have 3 wires on it doesn't it ?
                          Seeing that you do not have a CRO, doing repairs by remote control is difficult
                          Useing a multi meter you can test that the delay pot is probably functioning
                          with the power OFF, put your meter on pin5 of U4 and ground (0V) and twidle the sample delay pot, you should be able to see the resistance change
                          its a 10K pot so the resistance should change by about 10K, does that work ?
                          The trimmer pot R14 25K, all that does is set the MINIMUM delay, by turning the trimmer you should also see the resistance change..

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                          • #43
                            isopropyl spirit is better, not so toxic.

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                            • #44
                              Originally posted by 6666 View Post
                              Hello azigta, I have been following your progress and it sounds like you are close to getting the Barra working properly, but your pcb sounds like it still has some sort of problem, I have repaired a couple of these PCB's for a fellow here in Australia, he did some terrible things to those PCB's, but after spending many many hours on them I managed to get them both working, one was better than the other, these PCB's will tolerate a certain amount of soldering and un soldering before they start doing weird things after the tracks start lifting especially around VIAS, as you have done a lot of soldering and un soldering you probably have a build up of flux residue, have you cleaned the back of the PCB with Methylated spirit the Spanish name seems to be alcohol de quemar,

                              Useing a small tooth brush and some Methylated spirit gently clean the flux residue from the PCB, let it dry, you will probably have some white residue left, clean this off again, let it dry, the flux build up can cause some erogenous signals on the pcb and a clean pcb is a good place to start .
                              You say the delay POT does nothing, if does have 3 wires on it doesn't it ?
                              Seeing that you do not have a CRO, doing repairs by remote control is difficult
                              Useing a multi meter you can test that the delay pot is probably functioning
                              with the power OFF, put your meter on pin5 of U4 and ground (0V) and twidle the sample delay pot, you should be able to see the resistance change
                              its a 10K pot so the resistance should change by about 10K, does that work ?
                              The trimmer pot R14 25K, all that does is set the MINIMUM delay, by turning the trimmer you should also see the resistance change..
                              Hi, thanks, I have tested both r14 and the 10k delay pot measuring that pin and they do work. I couldn't know if they were working because I didn't notice any difference. I cleaned the board with 96º alcohol which is the only alcohol I have and then cleaned the white residue, but it still detects at the same depth, which I said 8cm but for coins Is like 2cm, screwdrivers and such do work on 8cm.

                              Thanks for the reply, I appreciate a lot any suggestion, if you have more ideas tell me and I will do everything I can to do it. Thanks

                              edit: The delay pot only has 2 wires, but I've soldered with a wire to connect pin 3 and pin 1 on pl2 in the pcb, so It doesn't matter which way you put the pot.

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                              • #45
                                Can you have a look at R7, R5, R16, no need to remove from PCB, just check the correct value.

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