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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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    You can't use an agc circuit because it will make the output of both COILS the same no matter where they are in relationship to the wire.
     
  2. camerart

    camerart Active Member

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    Hi Ronv,

    What I was trying to do was add the TL081 to your suggested Amp, for maximum Amplification, which on the simulator seems to work and 'sees' below 1mV by changing R2 and R4. (This then overloads easily) and if R2 and R4 are changed it will then 'see' 10V. Then to add some sort of circuit to shrink the Amp effect as the signal goes up so that it sees low and high. 'say' 1mV up to 10V.

    I have heard of Logarithmic opamp circuits that do just that, and thought that's what the AGC did, but now I am corrected.

    Tell me if you think this is a good idea, or perhaps make R2 and R4 Pots.

    Cheers.
     

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    Last edited: May 4, 2011
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    D2 is a "clamp diode" prevents the input of the LM339 from going more negative than about -0.7V but the LM339 must not have its input go more negative than only -0.3V.
     
  4. dave

    Dave New Member

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  5. camerart

    camerart Active Member

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    I have come across this before with LM324.
     
  6. ronv

    ronv Well-Known Member Most Helpful Member

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    The single TL081 does not have enough bandwidth (3 Mhz) to run with the gain you have attempted to get from it.
    In addition the low input impedance (1K) will lower the Q (and gain) of your resonant circuit.

    Are you thinking of a new design?

    I've not had problems with the clamp diode if the input current is low. But to make it sure you can use the circuit shown in figure 10 of this application note.


    http://www.electro-tech-online.com/custompdfs/2011/05/AN-74.pdf
     
  7. camerart

    camerart Active Member

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    I don't understand bandwidth or impedance or Q, All I can do is copy circuits and make them, with a little knowledge.

    If you mean I'm attempting to get 1mV to 10V out of it, I was trying to see if the Opamp could be adjusted down as the voltage went up.

    While waiting to test the 'original' circuit, (it arrived in the post today), I'm trying previous suggestions from this long thread, on a simulator, so I can learn a bit.

    I will try Fig 10. I am interested in other circuits, if they are more reliable. Basically I just wish to use the Cameras without having to worry about the electronics.
     
  8. ronv

    ronv Well-Known Member Most Helpful Member

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    Lets say everything is working at nominal and you get a 2.5 volt output. Now it you move one COIL closer and one further away from the WIRE what would the lowest and highest voltage be.
     
  9. camerart

    camerart Active Member

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    Because of the wide range of voltages, I thought I needed 1X COIL Amp for each Set of COILs and WIRES.

    I was going through notes and memories, of past testing, of different COILs different WIREs different Sig Gens, and was looking into the possibilities of 1X COIL Amp Circuit the would cater for the full range. The range across all situations is 0.1mV to 10V. And this input should give 0V to 5V DC. I think also it is better that this is by controlling then output not clamping it.

    As a usable circuit for many other applications I'm sure it would be good to go down to near 0V and have an adjustable high range.
     
    Last edited: May 5, 2011
  10. ronv

    ronv Well-Known Member Most Helpful Member

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    COIL Voltage Range

    I'm not sure this method will work for what you want to do. Is it your intent to adjust focus, F stop etc.?

    See if you can fill in the question marks in the picture.
     

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  11. camerart

    camerart Active Member

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    I think it will be easier not to think of COILs and WIREs, these seem to be causing a lot of complication.

    If it is possible to simply think of a circuit that can 'see' between 1mV and 10V Dc and output 0V to 5V Dc. Is this possible?
     
  12. ronv

    ronv Well-Known Member Most Helpful Member

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    Is that really the right question? Don't you really want an input from1 mv to 10 volts and an output from say 1 volt to 5 volts?
     
  13. camerart

    camerart Active Member

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    I'm not sure. I thought that a PIC chip A/D input went from 0V-5V, but I don't really mind. The wider range is best. I suppose input of 0V to 10v and an output say 0V to 5V, is the best question. Perhaps this isn't possible.

    From my limited knowledge, because the signal is sometimes tiny, the lower end of the input range needs stretching therefore the upper end would have to be shrunk, I think this is called Logarithmic. The output would be better if it is Linear. The reason is (Correct me if I'm wrong) that 0V to 10V, has 10,000 single mV and the A/D PIC input has 256 steps, so if it was simply divided it would only step every 39mV. Does this make sense?
     
  14. ronv

    ronv Well-Known Member Most Helpful Member

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    Camerat,

    I think this thread is getting to long. Maybe you should start a new one so you can get some different input.
     
  15. camerart

    camerart Active Member

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    Hi Ronv,

    OK. I'm new to forums, and have learnt a lot, about how to phrase the initial question. I have had some interesting answers in this thread, and really appreciate your time and patience. Thanks.
     
  16. ronv

    ronv Well-Known Member Most Helpful Member

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    I'm watching your new one and you are getting some good input!
     
  17. camerart

    camerart Active Member

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    Hi Ronv,

    True.

    I think we were nearly there, before. But of course. I'm only guessing.

    I think, the Circuit that you suggested (LM339 TL1013) that seemed to work ok, with a Fet Opamp at the front (Say TL081) would go as low as 1mV. With modifications: 1/ To stop the input pin going below 0V, and 2/ A feedback control on the TL081 to lower the gain as the signal went up.

    I can play with these ideas, on the Simulator. But I'm not expert enough to know quite what I'm doing.

    Cheer.
     
  18. ronv

    ronv Well-Known Member Most Helpful Member

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    Post the numbers when you get your new board.
     
  19. camerart

    camerart Active Member

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    Hi Ronv,

    Yes, I'll post them but what are numbers?

    Cheers.
     
  20. ronv

    ronv Well-Known Member Most Helpful Member

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    The amplitudes from the long wire.
     
  21. camerart

    camerart Active Member

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    Ok.

    I'm studying Opamps, but they are complicated little blighters, aren't they.
     

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