can't complete this circuit

Discussion in 'The Projects Forum' started by Adamf001, Jul 2, 2012.

  1. Adamf001

    Thread Starter Member

    Sep 5, 2011
    67
    2
    This may seem like a stupid question, but never the less I will ask it,
    The basic circuit that is made will have a positive terminal and a negative terminal, now the circuit below has only a positive 12V wire,

    My stupid question is this, If I had a 12V "battery pack" what do I connect the negative terminal to? the ground
    also on a similar note, whilst converting a ATX power pack I noticed that there was only a +5.5V wire if i used this wire alone to light up a bulb what do I connect the opposite wire on the bulb to to complete a circuit?

    I always though the ground was for safety if a circuit had excess voltage it would be removed via the ground? Hopefully I am correct in the ground terminals function...

    for me this just doesn't make sense.

    Thanks for your Ideas
    Adam
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    Every power supply, like a battery, must have two connections, one connection to source the current and the other as the return path. That is, the current must have a return path to the power supply.

    For a single voltage positive power supply, the -ve terminal is usually connected to GROUND in your circuit.

    For the purpose of electronic circuits, GROUND is not necessarily a safety feature. It is a reference potential by which all voltage measurements are compared with. Just treat GROUND as a reference point. Sometimes this will be labelled as COMMON.

    For your circuit, connect the -ve terminal of the battery or power supply to the GROUND symbol as shown in the circuit schematic.

    In an ATX or computer power supply, the current return path will be labelled GROUND or COMMON.
     
  3. Adamf001

    Thread Starter Member

    Sep 5, 2011
    67
    2
    Ok thanks I see what you mean,
    so for this circuit shall I take it then that all of the GROUND symbols converge as the Ve-

    Thanks
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    Yes.

    The only problem is the TL081/082/084 is not a single supply op-amp.
    I have never seen it being powered from a single supply. Usually it requires a dual supply, +ve and -ve.

    Maybe this circuit will work because this is an oscillator circuit. I am not sure.
     
  5. Adamf001

    Thread Starter Member

    Sep 5, 2011
    67
    2
    Thanks Mr chips for the help, no doubt I'll need your expertise in the near future
     
  6. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    It looks like the circuit itself should work ok. The single supply is configured to operate as a dual supply by using the voltage divider with 10K resistors to create a midpoint voltage. This works because the common midpoint does not need to pass any significant current and merely acts to provide a virtual ground point.

    I've used this trick many times without any problems (sometimes using a voltage reference in place of the voltage divider), but generally, it is better to use a single supply opamp, unless there are other unusual considerations.
     
  7. afternath

    New Member

    May 7, 2012
    17
    0
    Exact but your triangle signal reference will be VCC/2 (so 6V to battery GND). It will depend on what you do next.
     
Loading...