Reversing Switches

Discussion in 'The Projects Forum' started by mikemwa, Jan 22, 2012.

  1. mikemwa

    Thread Starter New Member

    Jan 22, 2012
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    I have a project that I want to work on to open and close curtains. I want to have a cord on 2 pullies with a stop attached to it. There are 2 microswitches, switches or some kind of sensors in the path. There is a gear motor attached to one pulley. I want to push the push button and the stop will travel to one switch then stop. When the button is pressed again I want the stop to go to the other switch and then stop and so on. How would I wire something like this up? I want to do this as easily as possible.
    This is an idea of what I'm trying to do.
     
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Good evening Mike, and welcome to AAC.

    Commercial apparatus to achieve what you want is quite expensive and, in my experience, a tad unreliable. So I will be interested to follow this thread.

    Specific solutions depend very much upon the mechanical side of things, so perhaps you would like to flesh out the detail?
     
    Last edited: Jan 22, 2012
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Ahh, if this was actually something easy to do. I see nothing but complications in the specification itself.

    My first concern: Does it need to reverse travel while in motion? It might need to do that for the times the button is accidentally pressed, then you can catch it and close the curtain without first fully opening it.

    Should it time out? If the curtain normally opens in time T how many multiples of T are acceptable before some error is noted?

    Any operator feedback necessary? (Some lights to say open, opening, closed, closing.)

    It could be done with just one button and some relays but there is some logic to be worked out first. Being a microcontroller guy I'd actually use a micro as it would be the least expensive way to "logically" glue some buttons with some relays.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    The easiest solution I can think of is with a momentary button, a DPDT latching relay and two NC end switches. The picture is showing one end switch being activated (open) and the latching relay in the position it was to get the stopper where it is now, at SW2.

    [​IMG]

    When the stopper is in the middle (not activating any end switch) both end switches are closed. Every pulse to the latching relay coil by via SW3 can then change direction.

    Of course more sophisticated solutions are always possible (as Ernie said).

    The biggest challenge is probably the end switch mounted on a string.

    The string has to be guided near the switches so you are sure that the stopper device activates the switch. If it's a stell string it could be magnetized activating a Hall switch, it could also be a ring magnet activating a reed switch, may other scenarios are thinkable. (photo interrupter for example).

    With this supersimple circuit I showed you have to make sure that the stopper device cannot overshoot the sensor/switch, otherwise the motor continues running.

    In order to avoid that the direction is being changed while the motor is running one could think of a relay contact in series with the SW3 while both end switches are closed.
     
  5. mikemwa

    Thread Starter New Member

    Jan 22, 2012
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    ........................
     
  6. mikemwa

    Thread Starter New Member

    Jan 22, 2012
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    This might be the way I want to go. Seems fairly simple. Are those latching relays expensive? Where would I find one. I will probably be doing this around 5 volts.
     
    Last edited: Jan 23, 2012
  7. praondevou

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    What's the motor current (max)? And what's its voltage rating?
     
  8. mikemwa

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    Jan 22, 2012
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  9. praondevou

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    Jul 9, 2011
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    The best is to connect the motor to the load and measure the current with an ampmeter.

    Question: Does it have to be a momentary pushbutton or could it be a simple DPDT switch?

    I thought I'd seen single polarity latching relays but I can't find any.
    Maybe they don't exist.
    Existing latching relays use either two coils to switch the contacts or one coil with inverted polarity.

    Tell us if it can be a DPDT switch or not. If a momentary PB is necessary we have to think of something else.
     
  10. mikemwa

    Thread Starter New Member

    Jan 22, 2012
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    OK, here's some data for you to chew on. I took 3 readings at different voltages. No load, medium load and full load. Medium load is probably more than what would be normal. Full load is almost stopping the motor. I used a pair of long nosed pliers to put a load on the motor. At the higher voltages I couldn't stop the motor.

    No Load..................Medium load.............Full load

    ..6.5V./6.7MA............6.0V./50MA.............6.0V./70MA.
    ..8.5V./5.7MA............8.0V./50MA.............7.9V./90MA.
    12.3V./8.2MA..........11.5V./40MA............10.5V./130MA.
    16.4V./10.7MA........15.7V./60MA............14.0V./160MA.

    A DPDT switch should be fine. Just as long as the drapes open and the next time the switch is pushed or changed they will close and so on. I just want to make this as easy as possible.
     
  11. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Ok, if a DPDT switch is fine for you then you don't need a relay. Just a DPDT switch and two end switches.

    You should be able to find something like this :http://search.digikey.com/us/en/products/F2UEE/401-1223-ND/417517 anywhere.

    As for the end switches, can you take a picture of the string and the area where the stopper has to activate the end switch? As was pointed out, this is more of a mechanical problem. Find the right end switch and make sure it is activated by the stopper.. and there will be no overshoot.

    Edit:
    [​IMG]
     
    Last edited: Jan 24, 2012
  12. mikemwa

    Thread Starter New Member

    Jan 22, 2012
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    Looks like that might just do it? Seems simple enough. Now i just need to round up a switch and a few other parts. Thanks.
     
  13. SgtWookie

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    Jul 17, 2007
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  14. BillB3857

    Senior Member

    Feb 28, 2009
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    SgtWookie.....

    As many requests as there are for reversing circuits for DC motors, would it be a good idea for the many variations of your relay reversing circuit made into a collection and made a sticky on the Project page?
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    I might throw them all in a blog. I've never started one.

    But, a reversing relay thread could be helpful to a lot of folks. It does seem to come up very frequently.

    That's not a project for me to undertake at the moment. Both my computers are offline. I'm on a "WebTV" kind of thing, and have no way to manipulate/upload/download images or schematics. It takes me much longer to do anything on this WebTV than it does on either of my computers. I may be offline starting late this afternoon for several weeks during my recovery period; I simply don't know.
     
  16. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Hey , welcome back , Sgt Wookie.
     
  17. mikemwa

    Thread Starter New Member

    Jan 22, 2012
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    Thanks for the help everyone. I'll run out and get a few parts and let you know how it goes.
     
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