Switching polarity

Discussion in 'The Projects Forum' started by Dr.Fiero, Jul 12, 2012.

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  1. Dr.Fiero

    Thread Starter New Member

    Jul 12, 2012
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    What I'm trying to do, is have a short output pulse of 12vdc (possibly around 1A) for about 3 seconds when 12vdc is applied to my circuit, then when power is removed from the circuit, have the same lines reverse polarity.

    The output lines can float at any other time.

    Obviously, I need a ground, constant power and switched power lines.

    This of course could be done manually with a center off DPDT switch... But you know... That's just too low tech. :)

    Any quicky ideas I could start with and build outward from?


    Thanks!
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    is a DPDT relay too low tech?

    Not everybody shares my view, but it's a pet peeve of mine to intentionally make things more complicated than they need to be.

    but if you insist, and a relay is too stone age for you, then next thing is an H-bridge
     
  3. Dr.Fiero

    Thread Starter New Member

    Jul 12, 2012
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    No way! I'm totally down with the low-tech from that angle.
    An actual DPDT center off relay is probably too expensive I'm betting, but it's easy enough to set up a pair of "normal" SPDT ones as such.
    I've used them for doing power window motors, and tiny push buttons.

    So that takes care of the heavy current part.

    Timer portion -- 556 maybe? One section for 'power on' phase, one for 'power off' phase.
    Then if either transit time was different, they'd be individually adjustable (bonus!).
     
  4. #12

    Expert

    Nov 30, 2010
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    Here's an idea to get 3 seconds. I can't understand what you want the polarity reversal to do, so this is what I can contribute. You adjust the 68k resistor to get the timing right.
     
  5. Dr.Fiero

    Thread Starter New Member

    Jul 12, 2012
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    Sorry! My bad... should have gone into more detail.

    I have a retractable plate holder. It comes with a remote control to extend/retract the plate. But I'm worried that one day I'll forget to kick the plate out before I drive off. I think it's about $150 fine. :(

    So...
    1) Power/key comes on.
    2) Magic-mystery-Box (MB) applies +/- 12VDC to plate holder for 3 seconds or however long it actually takes to extend.
    3) MB sits quietly with floating 0V outputs
    4) Power/key goes off.
    5) MB applies -/+ 12VDC to plate holder for 3 seconds or however long it takes to retract.

    The plate holder is just a tray with some pulley and cables, driven by a small DC motor. The transit times vary for in & out (damn gravity!) hence why I wanted to make the timers variable.

    I had considered doing it with an Arduino since I've now made a couple of things with them. And considering how cheap they can be had... it might still be a good option! Just have it drive the old-school relays directly, or semi directly. Of course, then I'll be forced to add all sorts of blinky LED's for "open" "close" "in transit" and who knows what else?! :eek:
     
  6. #12

    Expert

    Nov 30, 2010
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    Fooey. That circuit I did won't clock again at "power off".
    I'm not very good tonight. I'm going to bed now.
     
    Last edited: Jul 12, 2012
  7. BSomer

    Member

    Dec 28, 2011
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    uh... What is a "retractable plate holder"? Are you referring to a license plate on your vehicle? If so please read the Terms of Service. Automotive modifications are not a subject that is allowed for discussion here.
     
  8. Dr.Fiero

    Thread Starter New Member

    Jul 12, 2012
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    Really?! Well... considering almost everything I do is automotive related (cars & electronics - they're my hobbies, what can I say!)... I guess I'm done here.

    Pretty odd entry for a TOS I must say. I can see no pron, commercial stuff, profanity. But cars?! Lucky I didn't say it was for a motorbike or something worse.

    Anyhow - I'm just going to go the Arduino route. They don't care what I use it for. ;)
     
  9. BSomer

    Member

    Dec 28, 2011
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    I think that it is more of a liability issue than anything. For instance if someone here gives another person advice and the advice actually compromises the safety of the vehicle on the road. This could be a bad thing for the people involved in the discussion, other drivers on the road, and the forum.
     
  10. Dr.Fiero

    Thread Starter New Member

    Jul 12, 2012
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    Ok, I can see that if it involved the braking system etc.
    Of course, I have no idea how the thousands of purely auto forums have survived all these years ... especially with all the horrid info people dole out daily on them! Trust me, I've had to correct a lot of them over the years. Don't think anyone has ever been sued over it though.

    Ok, well lets pretend that this isn't for a car. It's a ventilation system door.... for my grow op. What. Nobody said anything about drug paraphernalia related being not permitted. :D
    (guess I'd better read the fine print in the TOS before I say that!!!!)

    {note: the above statement is made purely in jest for satirical purposes. No actual actions have ever been made, nor will be made by the poster. The owners operators and readers of the forum can in no way be held liable in part or whole for this post, nor past or future posts that may or may not be made by myself, relatives or anyone possibly affiliated with myself}
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    The owners of All About Circuits has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    Quote:
    6. Restricted topics. The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

    • Any kind of over-unity devices and systems
    • Automotive modifications
    • Devices designed to electrocute or shock another person
    • LEDs to mains
    • Phone jammers
    • Rail guns and high-energy projectile devices
    • Transformer-less power supplies

    This can be found in our Terms of Service (ToS)

    Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

    Please try to understand the reasons behind this action, and feel free to browse and use the forums.

    You might find answers to your questions in one of these forums:

    http://forum.allaboutcircuits.com/sh...ad.php?t=54400

    Another good forum that shares many of the same membership is http://www.electro-tech-online.com/ . Good luck.
     
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