Multiple circuits and one power supply

Discussion in 'General Electronics Chat' started by RayInMS, May 22, 2013.

  1. RayInMS

    Thread Starter Member

    Dec 12, 2012
    89
    1
    I'm working on a project that will incorporate several test circuits into one instrument case. The circuits are simple (e.g., 555 astables, etc.). I'd like to use one power supply to run the whole thing.

    Because no two circuits would ever be in use at the same time, I'm assuming it will be possible to run the circuits in parallel as long as I connect a diode between each circuit's ground/negative lead and the power supply's ground, as presented below:

    (-) Lead -> (A) Diode (K) -> (-) Battery


    Am I on the right track here? I'd like to avoid using a six/deuce rotary switch or anything like that to switch power from circuit to circuit.

    Thanks. :)
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,421
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    You have to state the current draw for each circuit in order for me to give you proper advice.
    Usually one would just connect all the circuits to the one power source and be done with it, no diodes required.
     
  3. ke5nnt

    Active Member

    Mar 1, 2009
    384
    15
    Another option I'd look at is, since you say only 1 circuit would be on at a time, how about a rotary selector switch? Connect power to the switch and then whatever position the switch is in is the circuit that's on.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    He did say he would like to avoid using a switch.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Can you give us a drawing of what your after?
     
  6. RayInMS

    Thread Starter Member

    Dec 12, 2012
    89
    1
    Sorry for the late reply. I'm away from my office so I'll have to upload pics later.

    The current draw is minimal, the supply is a 9V wall wart. I was going to attach each positive lead to a momentary push switch, then to V+. Then each negative/ground lead to a diode, then to V-. I'm worried that current could go up the negative/ground leads of the circuits not in use if a diode wasn't there to act as a gate. I know it'll create a voltage drop, but the circuits all pull minimum amounts of power.


    Power +-----------------
    ...|..............|
    Circuit 1+ Circuit 2 +
    ...|..............|
    Diode....... Diode
    ...|..............|
    Ground----------------


    I know the above pic is a poor representation (think of the dots as invisible). I'll get some better ones when I get back to the office.

    Thanks again.
     
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Dont see the point in the diodes as they will conduct when the power is applied, if you want to isolate each circuit use a rotary switch.
     
  8. RayInMS

    Thread Starter Member

    Dec 12, 2012
    89
    1
    The point of the diodes was to prevent current from backing up the negative/ground connections of unused circuits.

    However, I came up with a much simpler solution. I'm just going to add the switches to the ground leads of each circuit. That solves my issue and eliminates the need for diodes or other extra stuff.

    Thanks for the comments, as always. :)
     
  9. MrChips

    Moderator

    Oct 2, 2009
    12,421
    3,356
    Diodes are unnecessary.

    It is preferred practice to put the switches on the supply side of the power supply and not the ground side.

    Why not leave all circuits connected to the power?
     
  10. ke5nnt

    Active Member

    Mar 1, 2009
    384
    15
    Whoops, not sure how I missed that. Sorry.
     
  11. RayInMS

    Thread Starter Member

    Dec 12, 2012
    89
    1
    Because thecircuits are unrelated and independent of each other. Wouldn't connecting them in parallel willy-nilly be bad practice? How would you go about it? Pics. Would be helpful.
     
  12. MrChips

    Moderator

    Oct 2, 2009
    12,421
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    Connecting many devices to the same power source is not uncommon and is not bad practice. The reasons for not connecting them together would be to avoid

    1) excessive power consumption
    2) interference

    The solution is to put an ON/OFF switch between the power source and the device.
     
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