Predetermine stop start of dc motor

Discussion in 'General Electronics Chat' started by JohnBreeds, Feb 28, 2014.

  1. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    Hello Guys

    I'm trying to make a toy Hickory Dickory Dock for the local playgroup.

    Imagine a piece of plywood about 15 inches high and say, 4 inches wide, to represent the grandfather clock.

    For a bit of fun I want to incorporate a mouse that runs up and down each side.

    I know that I can do this with a couple of 6v dc motors; a couple of furry mice (not real ones) attached to some cord looped round some pulley arrangement.

    However, how can I control the ‘start’ and predetermined ‘stop’ positions of the mouse (ie before it runs over a pulley and jams)?

    I thought of tagging the cord so that it runs over a micro switch but this would just shut down the power for the whole lot. I want to be able to restart the motor but reversed – so that the mouse runs back down again, etc.

    Any ideas please?

    Oh, and before you say – I really do NOT want to spend the next 12months training a couple of mice J

    John
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
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    All depends on what starts the motor.

    Will you have one button for up and another for down?

    Or a switch? Flip it one way, it goes up and stops. Flip the other way, it goes down and stops. (easy way)
     
  3. inwo

    Well-Known Member

    Nov 7, 2013
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    Here is a diagram with a switch..............
     
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  4. inwo

    Well-Known Member

    Nov 7, 2013
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    And the hard way.
    With one push button.
     
  5. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    Oh Thank You so Much
    I had already figured the attached circuit as the simplest. As you can see it's just DPDT with center zero for 'off'. In this way I can reverse the direction of the motor and thus the mouse.

    But I just don't know how to stop the motor after the mouse has travelled say 14" to the top. At this stage the Clock's top structure hides the mouse.

    After suitable byplay with the kids I can toggle the switch so the mouse runs down again.

    I do like the idea of a magnet in the mouse and a reed switch (in motor circuit) placed near to the top. But of course once power switches off it shuts down forever (unless I physically give the furry thing a nudge).

    You will see on the attached sketch that I have 'doubled -up' the mouse arrangement. This is so that while I'm looking at the LH side for the mouse, he runs down the RH side (which I don't see - but the kids do and will roar!)

    John
     
  6. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    Hey this is GREAT!

    Is your middle name 'Genius'?


    I think this will work (using the reed switches and magnet in mouse).

    You will see from the sketch my other post that I was half way there :confused:

    Thank you so much.

    John
     
  7. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    832
    If you are willing to toggle the switch to change the direction of the motor, why not use a 3PDT switch. The third pole can be wired in parallel with the reed switch so that when the mouse is going down, power passes through the alternate path of the 3PDT switch. Once the mouse is away from the reed switch, it can go both up and down.

    I'm in a waiting room, otherwise I'd draw a diagram.
     
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  8. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    Hey - This just gets better! Your suggestion would meet my requirements perfectly.

    Thank you.

    I'd appreciate a quick sketch (as I can only think in pics).

    Thanks again

    John
     
  9. inwo

    Well-Known Member

    Nov 7, 2013
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    You only need a 2 pole switch either way.

    The diode method makes wiring simpler. As just one wire is looped thru the switches.

    Here's another way.
     
  10. inwo

    Well-Known Member

    Nov 7, 2013
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    To simplify:

    1. Put the reed switches in the red and green switch jumpers. (your drawing)
    2. Reverse your supply connections to the switch with the motor connections.
     
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  11. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    Thanks for this - I'm going to try this out.

    But on (2) how does this affect outcome?

    John
     
  12. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    That's great. Thank you.

    Just one thing though - what is the significance of your point No 2?
    Why would it make difference?

    Best

    John
     
  13. inwo

    Well-Known Member

    Nov 7, 2013
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    You're right.
    There are so many combinations.:D

    I was just thinking one way and didn't check to see if it would work the other.:p
     
  14. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    Tut tut! And I thought you were perfect! :)

    John
     
  15. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Here is the circuit I had in mind. I have some notes at the bottom. One I forgot to add, is this is the view from the bottom of the switch; the toggle positions may be reversed in operations.

    [​IMG]

    NOTE: Wait for it. Better idea coming
     
    Last edited: Mar 2, 2014
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  16. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    OK, in this circuit, you only need a SPDT toggle switch and two reed switches. One for when the mouse is at the bottom position and one for the top position. It runs in one continuous loop, so there is no need to reverse the motor direction.
    [​IMG]

    I've checked the logic of the various combinations of sensors (reed switches) and toggle positions, and believe this is a consistent design.

    Reed Switch Top Reed Switch Bottom Toggle Position Result
    open open X undefined/impossible
    closed closed X mouse moves to next position
    closed open Up mouse up
    open closed Up stopped
    closed open Down stopped
    open closed Down mouse down

    Hopefully, you'll find this simpler and can find a use for it. Members, any comments welcome.

    dj
     
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  17. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    Ha ha! Okay I'm waiting... :)

    But seriously; with your suggestion there is only one reed switch. This means that there is no limit stop on the mouse when he gets to the bottom of the clock - Is this assumption correct?

    Thanks everso for your help.

    John
     
  18. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    So sorry - our posts crossed at same time period.
    You're too quick! :)

    Anyway, thanks for the thought you've obviously put into this project.

    In the model shop in Swindon today I found a way of swivelling the mouse as he goes up then turns to come down.
    But in practical terms there's no need for this - just keep the mouse in a horizontal position.

    I'll be back...

    John
     
  19. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    Thank you for reply dj.

    Our answers crossed in the posts.

    Your simplified solution is very neat and elegant.
    But as you pointed out the mouse will go around in one continuous loop (thus obviating the need to reverse the motor polarity).

    For my purposes I need the mouse to travel either up and down along the same track.

    John
     
  20. JohnBreeds

    Thread Starter New Member

    Feb 28, 2014
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    I think the solution offered in post #10 will meet my needs.

    Thank you gentlemen. You've all been a great help and stimulated my old grey cells.

    John
     
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