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Discussion in 'General Electronics Discussion' started by MeAndSteve, Jan 20, 2012.

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  1. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    Hi all, not sure if this is the right place to post this, (play new guy card). :D

    I'm trying to get a garage door opener to function up and down with a single door bell switch and a single touch of the switch so you don't have to hold it down. Not sure if it's even possible. I'll be using limit switches to stop the door when it's all the way open as well as closed.

    Thanks for any help!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Presumably you're not using a controller that already has a single button that performs the press once to go up, press again to go down function?
     
  3. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    That is correct, Steve. At present I have the door, the motor, and the switch.

    Thanks!
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I'd try to get a proper controller for it. Typically these will stop the door either when a limit switch is actuated or when the motor current exceeds some value.

    You could design one, but I'd see if I could grab one from a door that has been replaced or from a failed control. They typically fail (so I'm told by people who look after them) because the relays fail. It's a very cheap fix.

    If you want to build your own, you'd probably be best to look at something based around a microporcessor.

    What's your skill level with designing things like this?
     
  5. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    I kind of thought that just buying a premade unit if they existed would be the easy way to go. For what I plan on using it for however, I wanted something sort of my own and it would need to be highly reliable. I studied electronics years ago but have very little design training/experience. I can easily follow schematics and build boards via schematics. I've been an automotive tech for over 20 years, so the hands on is easy for me, just designing a circuit is pretty much out of my ability zone.

    Thank you for your thoughts, at least I now know it is possible to do what I need so I can search out the design and cross it into a reliable usable unit.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I looked for designs on the web, but couldn't come up with anything.

    It's not a difficult thing to do, but ig you're moving something with significant mass, or with a motor that generates significant force, it is always wise to design it for safety.

    As an example, people have been crushed under garage doors. This is one reason why most modern controllers monitor current to the motor and stop (or even reverse) when they detect a stall.

    Simple limit switches are easy, but may not be sufficient.

    So what are you planning to do?
     
  7. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    There's allot to consider, I know!

    Truth be told, I'm working on a sliding door that will open when an alarm goes off without human intervention. But the door will need to be operational during normal use when the alarm is silent. I already have a working model of this built, just having some difficulty with the human operation side of things.

    I thought about the crush factor. I am planning on using the same type of control that is used in higher end automobiles for the power windows. They call it pinch control. If the automatic window is closing and something (childs fingers for example) are in the path of the glass, the window will stop and go back down. The limit switch will shut down the power if full open/closed position is actually reached. These portions of my project are not yet built.

    Thanks again for you help!
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    One way to detect the blocking of the door is to monitor the current through the motor. If it reaches a certain (high) value, you assume the motor is stalled and do *something*.

    Limit switches are typically hard wired in such a way that they will remove power from the motor even if the rest of the circuit is still commanding that the motor continue to operate.

    A simple example of a limit switch for a motor that can run in either direction is to have a blocking diode in series with the motor. This is normally shorted out by a switch, but this opens when the door (in this case) reaches the end of its travel. The diode prevents further current flowing in that direction (thus stopping the door). However it allows current to flow in the opposite direction (to open it). A similar technique is used at the other end of travel.

    Another method would be to place the switches in series with relay coils. My garage door uses two SPDT relays to control the direction of travel. The limit switches could interrupt power to the relay which initiates movement in that direction. The problem here is that since the limit switches do not directly interrupt power to the motor, a failure in the relay (stuck ON for example) will cause the limit switch to be ineffective.

    Going back another level to having the limit switches as inputs to a microcontroller, you have the problem that if the program crashes while the motor is turned on, the limit switch indication may be ignored.

    To detect a stalled motor, the easiest thing is to detect excess current through the motor. This can be as simple as connecting a transistor across a current sense resistor so that a logic signal is generated when the voltage across the resistor exceeds 0.7V

    What you do with this logic signal is then up to you, but note that using it to simply interrupt power to the motor is insufficient. It needs to feed back to the logic to stop or reverse the commanded action. You also may need a slight time delay as the high current may also flow during startup of the motor.
     
  9. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    All very good points. Thank you for the input, it will be helpful as I see there are things I didn't consider that I will need to incorporate into my project.

    Just found all of my loose transistors have all been jumbled together thanks to a rogue feline. Time to search out how to tell the difference between an npn and a pnp transistor.

    The pain never ends!
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Surely they have type markings on them? The part numbers will tell you that.

    Otherwise you'll need a multimeter on a diode check range to identigy the base, and from the "direction" of the diodes you measure between BE and BC you can determine if it's NPN or PNP
     
  11. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    Most of them are marked but I can't seem to find the part # reference on-line, can't find my old data sheets either. They have been around a while, probably 10 years or so so they may have been superseded in part #. My DVOM has a diode function, just can't remember exactly how to test them for npn or otherwise. I'll search it out on Google today.
     
  12. daGenie

    daGenie

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    Jan 23, 2012
    Actually, i think i can help you with your original intentions mr. meandsteve.............a couple of ic's should do the trick..................although i have an idea of what the circuit would look like, there are still a few issues im dealing with in my design...............but if you're still interested, just holla back............peace
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Post a couple. I'll take a look.
     
  14. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    Thanks for the offer daGenie, but I believe I'm on the right path now.

    I'll post a few pics tomorrow night Steve, I appreciate it!
     
  15. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    Here's a pic of the most common ones I have. Sorry it's not a better photo, my camera leaves a bit to be desired. You'd think someone by now would have designed a circuit that you could build on a breadboard that would light an led if a pnp or npn transistor was inserted in the right place on the board, but not light for the other. Is that possible?

    Thanks again steve!!



    [​IMG]
     
    Last edited: Jan 24, 2012
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I can read a couple of them, but the most important thing is that they seem to have the terminals marked as E B and C, so that makes identification easy.

    If your multimeter has a diode range, you should expect an NPN transistor to look like 2 diodes with the cathodes connected at the base. A PNP will appear to have the anodes connected together at the base.

    There are devices which can check transistors. Here is a good example. There are also many simpler options. Somewhere in the middle are multimeters that have transistor test sockets (you can find them on some really cheap meters)
     
  17. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    Thanks Steve for the help. That DCA55 really looks like a good device to have. Great link.

    Thanks again!
     
  18. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    Ok, have another issue, I need a circuit that will take a single dc pulse of 5V and trigger a power supply that will remain on constantly until the door is open. I have the trigger circuit and the relay figured out as well as the door/motor stop, just having a tough time with the constant supply of power to the door motor from only a brief dc V pulse.

    I'm not really asking for someone to design a circuit for me, maybe just tell me where I can research and learn how to design this circuit myself.

    Thanks again!!
     
  19. scriberman

    scriberman

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    Jan 21, 2012
    Being a mechanic and not a electronics bod I'd use a self latching relay with a limit switch to cut the feed when door open?
     
  20. MeAndSteve

    MeAndSteve

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    Jan 20, 2012
    Thanks for the reply scriberman, I too am a mechanic! It's a great life huh? ;o)=

    I thought about the latching relay and limit switches but the application I intend on using this for will require a crush protection circuit. (Thanks Steve!) I'm going to try and decipher the pinch protection module found in car windows (auto windows) for that and I'm not sure I could make it work with a latching relay. It is something to explore however.

    Thanks again!
     
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