Ground? where to!

Discussion in 'The Projects Forum' started by paulepc, Apr 5, 2014.

  1. paulepc

    Thread Starter Member

    Apr 2, 2014
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    New to circuits, and been trying to get various op amps to work they all fail.

    On a split rail supply connecting +12 & -12 volt, where does the virtual earth connect to, there plenty of circuits to view but the earth symbol is shown but where is this connected to in the circuit.

    Thanks
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    The virtual ground is called common or COM. This is the 0V reference in your circuit. The symbol sometimes used to represent COM is an inverted triangle.

    Any part of the circuit that needs to be referenced to 0V is connected to COM.

    It is not always necessary to connect this to earth ground.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The op amp output is referenced to the the common (0v) of the +12v -0v- -12v supply.
    Max.
     
  4. paulepc

    Thread Starter Member

    Apr 2, 2014
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    Thanks, So on the split rail I have the +12 & Zero/common & -12 and the zero is the virtual earth.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes, correct.
    Max.
     
  6. paulepc

    Thread Starter Member

    Apr 2, 2014
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    Can you explain why this does not work .3 volts in to amplify to 1.5 volts
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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  8. MrChips

    Moderator

    Oct 2, 2009
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    Interchange the inverting and non-inverting inputs of the opamp.
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    AND, connect the node that is (the low side of the battery connected to the 2K resistor) to the center point of the +/- power supplies. We call this node Ground (GND).

    ak
     
  10. paulepc

    Thread Starter Member

    Apr 2, 2014
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    Thanks is this correct, i'll try it now
    Paul
     
  11. Johann

    Senior Member

    Nov 27, 2006
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    What ever the long device is on your output, should also be connected to GND.
     
  12. ronv

    AAC Fanatic!

    Nov 12, 2008
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    The ground should go to the non-inverting (+) input. The 1k is the input and should not be grounded.
     
  13. paulepc

    Thread Starter Member

    Apr 2, 2014
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    0
    I have a PWM signal passing through a RC low pass filter, The output from the filter is a small sawtooth waveform and I get .9 volts and 1.6 volts variation when I use a PWM transmitter as seen on the scope.
    How do I turn the small .9 volt 1.6 volt range to +/- 10 volt. If I put it through a second op amp the PWM waveform comes back in. Looking for a clean +/- 10 volt.

    Thanks Paul
     
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