Need help to pull to gound a 13vdc voltage via a 5vdc control voltage

Discussion in 'The Projects Forum' started by JamesCO, Mar 19, 2015.

  1. JamesCO

    Thread Starter New Member

    Mar 19, 2015
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    This may be real simple but I'm not anywhere close to an EE I can ask for help.,

    I have a +5vdc line that remains at +5vdc until I click a mouse to generate an event, Then the line goes to ground. (this is what I want) and after the PC controlled and timed event the line goes high again. (again, what I want).

    The device I'm trying to control has a +13vdc voltage on the line I need to control. It works by having that +13vdc on the control line and starts it's events when pulled to ground.

    So, In a nutshell I need to pull a 13vdc line to ground when triggered by the +5 volt line going to ground.

    It's a PC controlled event that will take the +5 control line high again(and thus placing the 13 back in a + state as well when it's in a resting state.

    I understand a 5volt spdt relay might work, but I have absolutely no idea how to wire it up. I'm not looking to goof with it once it's working. hopefully I've explained well enough for some step by step help. Thanks In advance. -Jim

    The relay is the standard Radio Shack 'micro pc type' 5vdc 1A variety with five poles. The two different voltages come from completely different places, and are not connected in any way, ground or otherwise.
     
  2. MCU88

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    Mar 12, 2015
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    Hello...

    You could use an transistor instead of the relay.

    [​IMG]
     
  3. MikeML

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    MCU88's circuit does the opposite of what you want. It grounds the 13V line when the 5V signal is high.

    How much current do you need to sink to ground to turn on the 13V circuit when the signal is low?
     
  4. MikeML

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    You don't need to shout. Go and read the problem statement; not just the title.
     
  5. MCU88

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    Oh I see it now. Sorry Mike.
     
  6. JamesCO

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    Mar 19, 2015
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    This drawing may help explain or it may further confuse.
    The current flows from left to right(ideally), ignore the arrow pointing right. It's there to show the 13vdc coming from the device that needs to pull low. Thank you for the help all
     
  7. MCU88

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    Hello....

    Here is the revised schematic & schema:

    [​IMG]
     
  8. MaxHeadRoom

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    Jul 18, 2013
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    You don't mention if both circuits share the same common (GND)? If you are coming off of a PC that may be high impedance output I would look at a fet , 2n7000 for example instead of bi-polar.
    The output of the 2n7000 could turn on a opto isolator 4n35 and use the output to sink the 13v.
    Max.
     
  9. MikeML

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    Sorry, if the signal is swinging from 5V to 0V, that circuit will never turn off.
     
  10. MCU88

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    Mar 12, 2015
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    Hello....

    I have posted an revised schematic. What do you think?
     
  11. MCU88

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    Arh yes potential difference. I never thought of this!
     
  12. MaxHeadRoom

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    If you just want to switch a 5v relay then the 2n7000 will do it, just use a N.C. contact instead of N.O. for inversion and the 13v.
    Max.
     
    Last edited: Mar 20, 2015
  13. JamesCO

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    Mar 19, 2015
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    As I mentioned in my first post, The circuits are completely separate, including grounds.
    the +5vdc is generated in a radio transceiver and runs into the event trigger/external sound card. I've checked this voltage and it comes from the radio and not the usb connected external sound card.
     
  14. MCU88

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    Mar 12, 2015
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    Hello...

    This is tricky to do with transistors because of the potential difference in voltages.

    Any expert can advise on doing it?
     
  15. MaxHeadRoom

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    Then either arrangements I suggested will work.
    Max.
     
  16. MikeML

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    Try this. R4 is not real; it just has to be there to make the simulator happy. WAG on the impedance of the PTT line.

    The ground on the PC end is real and inevitable. The radio side can be floating...


    31.gif
     
  17. MCU88

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    This one?

    [​IMG]
     
  18. MCU88

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    You just beat me in posting. I thought of the opto too.

    But for an greater challenge try and do it with just transistors....
     
  19. JamesCO

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    Mar 19, 2015
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    Thanks for the reply's,
    I'm not sure if I have completely explained what is happening.

    I'll simplify,
    I have a +5 voltage with a ground coming from an RCA jack. The center is + the outer is the - This is the control line,
    It plugs into the line I want to control. (assuming I can figure out how to interface)
    the controlled line has a +13 voltage and it's own ground (also RCA same as above) that needs to be grounded to turn on.
    The +5 voltage grounds itself when I tell it to.(and goes back high again when told)
    The device I need to control needs to be grounded to turn on and then go back high again when the +5 goes back high, in turn letting the 13 go back high and thus turning the device off.

    Hopefully that makes some sense.
     
  20. MikeML

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    I believe that my posting (#16) does all you said...
     
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