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Small signal to 5V output amp

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by camerart, Feb 24, 2011.

  1. ronv

    ronv Well-Known Member Most Helpful Member

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    I'm still not clear. How many turns on the coil and what diameter? You talked about shorter wires. What does that mean? Is it just a single turn? Can you make a picture?
     
  2. camerart

    camerart Active Member

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    The bit we are talking about is like this: Attached.

    The WIRE can be any length, the longest is perhaps 300 Yards/Mts. I measured 6-Ohm on the shortest WIRE and 27-ohm on the longest WIRE.

    The COILs I wound myself from experiments about 300 turns, with a tuning Capacitor, 3/4 inch long 1/2 inch wide APP.

    So basically all I need is to detect the WIRE by the COILs, the signal amplified and turned into as near 0V to 5V as possible (for A/D PIC inputs).
     

    Attached Files:

  3. ronv

    ronv Well-Known Member Most Helpful Member

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    Hmmm. Very interesting. What does this machine do?There is a lot working against you on the long wire:
    1-Resistance is higher
    2- Inductance is higher
    Both result in lower current.
    Is your long wire stretched out or do you have it coiled up?
    The current in the short wire is fairly high ~ 1.8 amps
    In the long wire maybe .25 amps - so a fairly big difference.
    If it is coiled up the inductance will really make a difference.
    Can you use more than 12 volts for the long wire?
    Here is a link to show how the field might look with various configurations.
    3-D Magnetostatic Field Simulation
     
  4. dave

    Dave New Member

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  5. camerart

    camerart Active Member

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    In brief:

    It focuses the COIL distance from the WIRE, in this case APP 100mm (4Inch) by giving an A/D signal to a PIC/Motor system which moves the COIL nearer or Further from the WIRE.

    1/ and 2/ I don't understand the effects of Resistance Inductance.

    The WIREs are never coiled up always stretched out in use.

    I can use any Voltage, but lower is better (safer) for me. Also I don't want to get into special insulation if poss.
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I assume there is a big loop of WIRE being fed from the high frequency signal.
    Then there is a toy car or something that has a pickup COIL and amplifier that detects the magnetic field from the WIRE and the toy car drives toward the WIRE or drives away from the WIRE.
     
  7. camerart

    camerart Active Member

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    Very similar.

    So, do you think the Ronv circuit + 2N3819 FET at the front can be made to work?

    I have tried to set-up 2N3819 FETS lots of times, and never quite got the hang of it. I understand how to do it, but the results have been varied and perhaps not reliable.

    Also how can I get a better signal into the WIRE. Bear in mind Battery life! 55+khz
     
    Last edited: Mar 30, 2011
  8. ronv

    ronv Well-Known Member Most Helpful Member

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    Getting information out of you is like trying to wash a cat. :)

    Is the wire stretched out for your tests, or only in use? If it is coiled up the inductance will be much higher.

    The small field around the wire depends on the current through the wire. The higher the resistance and inductance the lower the current. The larger the loop of the wire the higher they both go. If you have found a good level for the short wire you will need to make the long wire look like the short wire. To do this you would need to increase the voltage. But if you are running on little batteries the current will quickly make them go dead.

    You might want to think about a different way of doing whatever it is you are trying to do.
     
  9. camerart

    camerart Active Member

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    Hi Ronv,

    I did wash a cat once, but it was with a garden hose, so not

    difficult.

    Sorry that I am not good at explaining, I spend a lot of time

    composing answers, to be as clear as possible. Im sure if I

    explain the whole thing it will be far too complicated to

    explain clearly, this is why I have kept it as brief as

    possible, only concentrating on the weakest section, the

    WIRE/COIL to A/D bit. Once I get good A/D signals, the rest

    will work.

    In #64 I said the WIRE is always stretched out, never coiled

    up.

    I think if I simply stick to getting the long WIRE working,

    then I'm sure I will get the shorter WIREs to work.

    I think I understand your

    resistance/induction/voltage/current explanation. I'll do

    some tests with what I've got, with adjustments based on your

    answers.

    I use quite large Golf Buggy batteries, so I'll do a time

    test with them.

    I am happy to think about a different way of doing things.
     
  10. ronv

    ronv Well-Known Member Most Helpful Member

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    OK. A few questions:

    Since your long wire is 27 ohms it is 24 gage wire?
    Since the short wire is 6 ohms it is 222 feet?
    Does the circuit with the amplifier I sent you work at 222 feet (short wire)?
    I am assuming the coil is resonant at 50 KHz. Can you give me the diameter and length of the coil and the size of the tuning capacitor and we can make sure it is resonant at 50 Khz.
    If all is well then we can increase the voltage to the wire, but you will need to start with it low and make it higher if you get no signal.
     
  11. camerart

    camerart Active Member

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    For economic reasons I use found, scrap materials, spending more on better electronics, so the WIREs are all different. The long WIRE is single strand, 0.033Inch/0.84mm 27-Ohms. Your circuit +FET senses the short which is only about 25Ft. 'multi strand' WIRE and fraction of an Ohm (Sorry for the gigantic mistake, I was remembering another WIRE from a while ago) If we work on the long WIRE, then I will buy the same type of wire for other WIREs.

    The COIL/Capacitors are all different as experiments, but all tuned to 55.930Khz. It is possible that the tuning changes! At first the Signal generator was controlled by 555 chip @50khz then upped to 55.930Khz and controlled by a XTL. The last one has a POT just in front of the LM380 (See circuit I posted to you) so I can turn the output up or down. If I turn the output up on the shorter WIREs then the power transistors get hot, and I also suspect the Wave changes shape (distorts)
     
    Last edited: Mar 30, 2011
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A distorted square-wave looks like a square-wave.
    When the very low resistance of the shorter WIRE shorts the output from the transistors then of course they get hot.
     
  13. camerart

    camerart Active Member

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    I think you are correct, at the signal Generator it is a

    square wave. I have been watching the sign wave at the COIL,

    a test point on Ronv's circuit.

    When I get chance I will check with different waves at the

    Generator and COIL.

    As I got longer WIREs, I upped the Signal generator output by

    adding power Transistors, also a POT so I could turn it down

    for the shorter WIREs, that I use to test and experiment I

    also added a Heat sensor switch off on the Transistors.
     
  14. ronv

    ronv Well-Known Member Most Helpful Member

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    What is the shortest wire?
     
  15. camerart

    camerart Active Member

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    As long as I can lay it round my test area, the bit I usually use is as I said 10Mtrs and 1/4-Ohm.
    It could be any length, I have lots of scrap bits, and of course, if it is important I'll buy any length.
     
  16. ronv

    ronv Well-Known Member Most Helpful Member

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    Wire driver

    OK. Here we go.
    I think your driver is a little to slow for your frequency, so here is one using FETs.
    It is important that you use the FETs in the schematic or they may smoke.
    The input to the driver should be from your 555 oscillator because the other circuit won't drive them. The 555 should also run on 12 volts.
    The short wire should be at lease 10 meters and should be 24 gage. The wire may get to hot. I'm not sure. You will need a heatsink on the FETs.
    This should give you an output from your coils for the long wire of about twice as much as the 555 circuit gave you on the short wire. Use 2 of your 470 nf caps in parallel for the output.
    In real life do you need to run with long and short wires or is that just for test?
     

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  17. camerart

    camerart Active Member

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    Hi Ronv,
    Fantastic!
    True the short WIRE is just for tests.
    I assume that L1 is the WIRE, is this correct?
    Thanks very much.
     
  18. ronv

    ronv Well-Known Member Most Helpful Member

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    Yes, sorry I meant wire not coil.

    PS. The parts are available at Mouser.com in the US.
     
    Last edited: Apr 1, 2011
  19. camerart

    camerart Active Member

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    I will look for the components in the Uk first. Would the STP36NF06L work as alternative to STP20N06, as I have a couple?
     
  20. ronv

    ronv Well-Known Member Most Helpful Member

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    Should work good.
     
  21. camerart

    camerart Active Member

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    OK, all ordered. I'll have a go next week, thanks.
     

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