change polarity when power is off

Discussion in 'The Projects Forum' started by etminasm, Mar 24, 2011.

  1. etminasm

    Thread Starter New Member

    Mar 24, 2011
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    Hi,

    I am new in electronics. But I need to get a circuit, which can operate as follows:

    when added 12VDC , small motor will slide holder out. And when 12VDC will be off, it should slide holder back in.

    So I need to run motor for short time forward when 12VDC is on, and reverse, when 12VDC is off.

    I know, I need capacitor to collect the energy, but I do not know how to put everything together.

    Can somebody help me out on this?
    Thank you!
     
  2. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    Are you sure that's what you want? It would require a huge capacitor and is not practical. Perhaps you're describing a push button - tray out, push button again - tray in?
     
  3. etminasm

    Thread Starter New Member

    Mar 24, 2011
    12
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    :) thanks for fast reply..

    Yes, i know, maybe it's not practical, but task is like I have described.
    There is very small holder that needs to be moved forward when applying 12VDC. And it should go back when 12VDC goes off.
    I need just very smallest electric motor.

    Do you know any theory, how can this task be done and more 'practical'?
    I think I need 3 contact relay...
    And about capacitor. Can I connect several capacitors in series to build up capacity?

    I hope I haven't written any nonsence.. :)
     
  4. CDRIVE

    Senior Member

    Jul 1, 2008
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    Please explain why the power must be off when the tray is retracted. Also explain what device (switch, sensor, etc) initially triggers the motor circuit to open the tray. Is there human interaction?
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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    Also, is there a limit switch or some other form of power disconnect for the motor when the tray is at either position, extended or retracted?
     
  6. etminasm

    Thread Starter New Member

    Mar 24, 2011
    12
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    Ok, I'm not so good in english, but i'll try to explain..

    Actually I need it for my rear view camera , which i want to install on my car. But to prevent it from get stollen, I want to place it under cars back bumper. So now, when I put rear gear, cameras holder should go out. When I out forward gear, 12VDC is cut off, so camera should hide again.

    I have attached some paintings. It maybe will clear out what I mean..

    Thank you!
     
  7. etminasm

    Thread Starter New Member

    Mar 24, 2011
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    In the previous attached picture it is just my theory. will it work. I know, I need some more components beeing added to the circuit, but where to add them?
    What about capacitor? Is it possible to run engine from power colected in capacitor/several paralel capacitors?

    And one thing I forgot to say: BilLLB3857, there is no limit switch. But, yes, I need it.. But where to place it and what kind to use?

    I really appreciate all your help and time trying to help me!
     
  8. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    This is why I asked you why the power had to be off to retract the tray. What you're describing does not require power ever being off. Your plan of using the backup light voltage as your power source is where you're going wrong. That voltage should be used as a control signal only and power should be supplied by a separate wire connected to your accessories circuit or on a dedicated fused line. You'll have to install this new wire.
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    Here's a thought... If you have a courtesy trunk light (that comes on when the trunk is open) you can probably power your circuit from that line from the hot side of the trunk switch. This will eliminate the power wire I mentioned in my last post.
     
  10. BillB3857

    Senior Member

    Feb 28, 2009
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  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I've posted some electric motor reversing schematics before, but this is a different ball game. None of the circuits I've put together so far will work for this, as-is.

    The motor, wiring, switches and relays will all be exposed to the elements. I don't see electromechanical switches lasting very long in such a situation. Water, mud, vibration, etc. will cause things to fail quickly.

    I don't know how you plan on keeping the camera lens clean, but it's going to get very dirty, very quickly.

    Backup light - it's not known if the +12v side or ground side is switched to turn on the bulbs. Much of the switching nowadays is on the ground side.
     
    Last edited: Mar 25, 2011
  12. etminasm

    Thread Starter New Member

    Mar 24, 2011
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    that's a good idea CDRIVE. Off course i need to use separate power from the trunk light. But then i need to make everything to work, but i do not know how. what components and switches do i need? Can somebody help..

    BillB3857, this actuator seems that it would be ok. Do you know how much it moves out? I think, just about 1cm. But diameter of the camera is about 5cm.
     
  13. BillB3857

    Senior Member

    Feb 28, 2009
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    By mounting the camera on a swing down frame (hinge), the linkage point could be adjusted to give the proper amount of rotation. If you look here...........
    http://auto.howstuffworks.com/power-door-lock3.htm
    you can see the insides of a typical unit.
     
  14. soda

    Active Member

    Dec 7, 2008
    174
    13
    Hi

    Here is a schematic i made for my UV scanner project. Maybe you can do some changes to it to suit your needs
     
  15. williamj

    Active Member

    Sep 3, 2009
    180
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    etminasm,

    The easiest and cheapest way I can think of to accomplish your goal would be to mount your camera circuit in the trunk.

    Install the camera circuit in a project box, mount in trunk, drill one hole in trunk for camera point of view and seal. Sealing and weather proofing should not be all that difficult with all of the over the counter products that are available now. Mounting the project box with a silicon adheasive caulking would minimize the number of holes required. Placing the camera lense behind a modified (ie. small hole) automotive reflector would not only conceal the lense from public view but would also cover the hole should it ever have to be removed.

    As for powering your circuit do as suggested and power from the trunk lighting circuit but switch on/off from the backup light circuit. It's as easy and no more hazardous than tapping in for trailer lights. (see attached) The relay could also be installed in ther project box for nice clean install.

    williamj
     
  16. etminasm

    Thread Starter New Member

    Mar 24, 2011
    12
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    Hi CDRIVE,

    oh, yeh, maybe this is better to use power from trunk light, but what it is best to use in this case? relay? or transistors maybe? can somebody draw a circuit? what components and what nominals do i need?

    BillB3857, thanks for showing me the door actuator. It is in this way, what I need, but this actuator moves out just about 1cm? diameter of camera is about 5 cm
     
  17. etminasm

    Thread Starter New Member

    Mar 24, 2011
    12
    0
    Hi,

    sorry for repeating the post. I could not see, all you posts, before I have updated. Now I see..
     
  18. etminasm

    Thread Starter New Member

    Mar 24, 2011
    12
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    Thaks soda, BillB3857 for your ideas. Circuit is very nice. Door actuator is also very good idea.

    But I think, that maybe i'll try to do more simple, with no moving parts as williamj suggested. But williamj, what do you mean with 'project box'? Is it some simple box or what?
    And 'automotive reflector'.. What is that?

    Thanks for info!
     
  19. williamj

    Active Member

    Sep 3, 2009
    180
    32
    etminasm,

    A project box is just that, a simple box to contain and protect your project. They are generally inexspensive and usually made of plastic, however they can be made of anything from aluminum to stainless steel. Google electronic project boxes and you'll get a large assort to choose from.

    Automotive reflectors are also know as automotie safety reflectors. You usually see them on the sides and rear of trucks, busses and cars. The sole purpose of the reflector is to reflect the headlights of other vehicals so the drivers of those vehecals can more readily and easily see that particular vehical. The most common colors are red, amber or white but now a days most any color might be available. Again, Google is your friend. I just Googled and Amazon shows a package of twelve .5" x 1.25" reflectors for $4.09.

    A simple diagram is attached. Good luck with your project.

    williamj
     
  20. etminasm

    Thread Starter New Member

    Mar 24, 2011
    12
    0
    Thanks a lot williamj,

    that is really nice. Now I got it :) Very easy way to do it :) And I was trying to build a robo :)

    but you see, I'm thinking to by a rear view camera http://cgi.ebay.com/Car-Rear-View-C...290?pt=LH_DefaultDomain_0&hash=item3cb5cf7712

    Do you know if there are smaller ones in the market? Or do you think, that I could take that camera a part and use just lense and pcb from it (put in to project box)?

    I'm thinking about the hole size in my trunk :) Don't want to make a great canyon :)
     
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