Analog/Digital Grounds

Discussion in 'General Electronics Chat' started by NateG, Oct 10, 2008.

  1. NateG

    Thread Starter Member

    Jun 20, 2008
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    I am currently building a guitar synthesizer which uses a pickup that requires +5v, -5v with an analog ground which is then sent into a rectifier. On the other side of the rectifier I have another +5v source with my digital ground, which at the moment is completely separate from the first source.

    My question is, is there a way to power the first part of the circuit and the second part of the circuit using the same source without shorting the rectifier?

    I'm going to be using batteries.
     
  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    Can you give us a schematic? It's hard to answer without one..

    Steve
     
  3. NateG

    Thread Starter Member

    Jun 20, 2008
    22
    0
    Heres a schematic of my whole circuit in Eagle. I can also draw up another specifically for this question if its too confusing.

    The focus on my question is at the bottom of this schematic. There are 4 inputs coming off my guitar pickup (all thats shown here is the connector) and one ground for all four of these signals.

    These signals go through the rectifier, and into the rest of my circuit, where I have a completely separate source of power and ground (If I use the same source as my pickups the signal from the pickups disappears).

    My question for this is, is there a way to have one battery source power both the pickups and the board in this schematic but not short the rectifiers along the bottom?
     
  4. NateG

    Thread Starter Member

    Jun 20, 2008
    22
    0
    Is there a way to separate them with a resistor or inductor? I think I may have seen it done before.

    Im trying to minimize the amount of battery packs I have to use.
     
  5. NateG

    Thread Starter Member

    Jun 20, 2008
    22
    0
    The main reason I need the ground on both sides, is that I am making a comparator with a reference voltage that will need to have the same common reference as the rectifier in order to be able to compare them.

    In the past when I tried to do both to the same ground I ended up with no signal from the pickups, which I believed was caused by the short of one of the diodes in the rectifier.
     
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You can do it by using a half way rectifier rather a full wave rectifier or by using a more complicated circuit with transistors.
     
  7. NateG

    Thread Starter Member

    Jun 20, 2008
    22
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    Hmm, half wave rectifiers is a good idea, however I need a pretty smooth signal.

    You have any info about the transistor circuit?

    At this point im considering just using two separate battery packs and having one hooked up to an inverter for the pickup.
     
  8. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    How will you power your pick up?
    With two batteries or a positive/negative (bipolar) power supply?
     
  9. NateG

    Thread Starter Member

    Jun 20, 2008
    22
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    2 batteries linked together with the middle terminal being ground.
     
  10. NateG

    Thread Starter Member

    Jun 20, 2008
    22
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    just to see what would happen I tried setting up a half wave rectifier on a breadboard. Not sure if its the diode I'm using, but I seem to get much less signal than I do with the full wave rectifier.
     
  11. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Here is a circuit with op amps for a full wave rectifier. This is only for one output of the pick up, you have to use one of this circuit for each output of the pick up.
     
  12. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The average signal you get fro ma half wave rectifier is less than the one for ma full wave rectifier.
     
  13. NateG

    Thread Starter Member

    Jun 20, 2008
    22
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    Hmm, thanks Ill give that a try.

    Can I expect to get a higher voltage output from this one as well?

    And what opamps do you recommend for this application? I have some ad712s lying around, but I assume that they might be too noisy.
     
  14. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    If you want you can control the gain of the lower op-amp by varying R2 (you can vary R1 too but i suggest you to leave as it is as to keep the input resistance high-if you want higher input resistance you can change the resistors to higher ones but take care not to be too high because op-amps require a small bias current). For the upper op-amp, you have to wire it as a non-inverting amplifier to be able to control the gain.

    What is the maximum frequency the pick up outputs?
     
  15. NateG

    Thread Starter Member

    Jun 20, 2008
    22
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    Im not exactly sure of the top frequency, but I have to assume that it would be lower than 5 kHz. Of course, with harmonics and all, I cant be exactly sure.

    Highest frequency I will actually play is about 500 Hz

    Oh another thing, this wont cause any problems connecting the ac ground (of the signal being rectified) and the dc ground coming out the other side?
     
    Last edited: Oct 11, 2008
  16. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    I have read the specifications of the your op-amp and it is good for your application.
     
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