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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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    Coil amp

    His input to the circuit is a resonant coil. The low input impedance of the transistor circuit kills the Q.

    Let us know how it comes out.
     
    Last edited: Apr 29, 2011
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I would use a TL071 low noise audio opamp (or TL072 dual) that have Jfet inputs for a very high input impedance and as much gain as you want.
     
  3. ronv

    ronv Well-Known Member Most Helpful Member

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    But the paper is not blank anymore.
     
  4. dave

    Dave New Member

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  5. carbonzit

    carbonzit Active Member

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    So Ron, just curious how long it is until your patience with this guy runs out, with his WIREs and COILs and all.

    Does anyone even know what the hell he's doing with this stuff? any idea what the application is, what the physical configuration of these WIREs and COILs and whatnot is? what he's trying to control here?

    All I can say is, you're a better man than I ...
     
    Last edited: Apr 29, 2011
  6. ronv

    ronv Well-Known Member Most Helpful Member

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    I think it is something similar to a wire follower - not sure.
    It's almost always a problem when there is not a good spec., but sometimes it's not possible and things evolve.
     
  7. camerart

    camerart Active Member

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    Hi, Carbonzit,

    I mainly trying to control Cameras at a distance, but secondarily I am trying to learn about signals and pick-ups, that will most likely be useful for other things, perhaps WIRE following.

    I use the terms WIRE and COIL as in the past, a piece of wire has been mixed up with the WIRE with the signal in, and COIL similar.

    Ronv has been very patient with me, and i have appreciated this as I am not good at learning, but with his and others help I am slowly getting it. As he says, it is developing, so not easy to explain with a few words.

    Sorry if this has niggled you, it's not intentional.
     
    Last edited: Apr 30, 2011
  8. carbonzit

    carbonzit Active Member

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    Well, OK, that tells us a little about your application, but not much. Controlling cameras based on what? proximity of something to a long wire or a coil? (I ASS-U-ME that by "WIRE" you basically mean a long length of wire connected at only one end, essentially an antenna?) And what form/shape does the "COIL" take? Is it in proximity to whatever you're trying to capture with the camera?

    It would really help to know this stuff. Of course, speaking for the congregation here, we understand that you might not want to disclose proprietary information. But barring that, any details you can give--especially the physical layout of this setup--would help to give you better answers here.

    And you know, you don't really need to capitalize "WIRE" and "COIL" in your descriptions; we can figure out what you're referring to.
     
    Last edited: Apr 30, 2011
  9. camerart

    camerart Active Member

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    I though I had already explained much of this before.

    I use capitalise wire and coil mainly for my benefit, as I have difficulty reading (Dyslexia) So I use this method to enable me to see what i call important words at a glance.

    I have found that too much explanation about what I'm doing confuses the more interesting electronics part. Also it is developing as we go along, so I am changing things, to fit in with the advice I'm getting. Just doing my best!!
     
  10. camerart

    camerart Active Member

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    Hi Audioguru,

    I was trying to learn circuit simulation and have a couple of free programs. I was going to compare the 2n3819 Fet Preamp with this Darlington one, but from what you say, should I stick to the 2n3819?
     
    Last edited: May 1, 2011
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A Jfet does not have much voltage gain. Why don't you use an audio opamp that has Jfet inputs (like a TL071 or OPA134)? Its input impedance is extremely high and it has as much gain as you need.
     
  12. camerart

    camerart Active Member

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    Hi Audioguru,

    I have a complete circuit set-up from Ronv that looks promising and I will test properly when the conditions allow.

    Having said the above, I was playing with an idea, that if the signal could be amplified at the front of the circuit, then put through a logarithmic circuit, which might 'see' a small signal, then as it got larger would lessen as it passed through the circuit, so the output was controlled for A/D inputs. Would this work with a large range of signal e,g, 1mV to 10V?

    Does this make sense?

    I have some TL081CPs

    This is an idea but I don't know enough to make it.

    Cheers.
     
    Last edited: May 1, 2011
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    It sounds like you need an automatic-volume-control like were used on some tape recorders. It is also called a compressor/limiter and is used by radio stations.
    Usually it is very noticeable because when the sounds are low then it boosts their level and the level of noise. When sudden loud sounds occur then the AVC circuit responds too slowly giving a blast of very loud sound before it reduces the level. When the sounds suddenly go to a low level then they cannot be heard until the AVC circuit resonds by increasing the gain.
     
  14. camerart

    camerart Active Member

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    You are probably right. But perhaps it's best not to go further though, as I must test the Ronv Circuit first, before getting into another idea.

    Thanks.
     
  15. ronv

    ronv Well-Known Member Most Helpful Member

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    Correct me if I'm wrong, but I think you are trying to servo on the amplitude of the 2 circuits? So whatever the gain you have on one you need on the other.
    Since you have a micro I think I would just clamp the output to the A to D at 5 volts then let the micro set the gain to the input stages to bring them into optimum range (2.5 volts). (calibration) This of course would require a new design, but it's probably a requirement anyway. The next step would be to determine the maximum and minimum signal from the 2 different COILS when the gain is the same but they are at maximum and minimum distance from the WIRE. This spec. will limit how far away from the Wire the COILS can be, which may be another problem?
    It really would help if you could explain how you would like the whole system to work.
     
  16. camerart

    camerart Active Member

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    You are not wrong.

    But first I want to test your Circuit as it might work ok, and it's a holiday here (I need to get permission) this will take some time, as I am out of touch with PIC programming.

    I am not asking for help right now. I was looking at the circuits already posted, to have play with a Simulation program I've just got. I have suceeded in getting my first results on the simulator from the TL082 chip suggested by Audioguru, early days though. I had the idea that perhaps a circuit with high amplification at the front followed by a Logarithmic Amp to find out if this would 'see' a large range of voltage without overloading, as my first simulation.

    A bit of explanation of what I do, as I keep getting asked: I photograph wildlife and anything interesting, and have been interested in electronics for a long time, but never mastered it as you can see. I wanted to adjust Cameras at a distance and at first used radio control and Binoculars, then Wifi, with my sons help. Then I tried relaying the signal to get the long range. The WIREs seemed best, so here we are. I am also interested in Generators and I have designed a linear Engine with a Motor engineer. While he gets on with the engine side, my side is to design the electical side, this is where the coil experiments help my understanding. This technology lends itself to many ideas, and WIRE following has been suggested and sounds interesting, so these circuits might come in handy for that too. So now you know more than I do about what I'm up to, I hope it helps.

    Cheers.
     
  17. carbonzit

    carbonzit Active Member

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    So you basically want to remotely control a digital camera from a distance, correct?

    Sheesh. What a wild goose chase this whole agonizing exercise in ADD has been.

    Don't you realize that there are perfectly good, tested and debugged solutions for this available?

    What kind of distance are we talking about here, anyhow? yards? hundreds of yards? miles?
     
  18. camerart

    camerart Active Member

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    Hi Carbonzit,

    1/ correct, but if the circuit can also be used for other applications, this is better, isn't it?

    2/ Sorry, perhaps you shouldn't be following if it is agonizing for you. I might point out that it is very difficult for me also.

    3/ No I didn't realise.

    4/ It has been explained in the past.

    cheers.
     
    Last edited: May 2, 2011
  19. camerart

    camerart Active Member

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    Hi Ronv and all,

    I have been trying out a Simulator.

    First I tested your circuit (Attached) This worked fine.

    Then I added an AGC circuit suggested by a friend, but never tried. (Attached)

    Will you have a look please and see if it looks like it might work.

    Cheers.
     

    Attached Files:

  20. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Your AGC circuit has too many things wrong for me to fix it. Look in Google for a good one that uses a single polarity supply.
    Your "clamp" diode allows the input of the comparator to go too low below ground which messes up its output polarity.
     
  21. camerart

    camerart Active Member

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    Hi Audioguru,

    OK. The circuit on the PNG attachment is working ok, for weak signals (1mV ish) and an AVG was suggested to stop it overloading as the signals got stronger, perhaps up to 10V.

    Which one is the 'clamp' diode?

    At the moment I'm only practising on a Simulator.

    Thanks.
     
    Last edited: May 4, 2011

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