I do need help

Discussion in 'Wireless & RF Design' started by GeorgeRB, Oct 9, 2012.

  1. GeorgeRB

    Thread Starter New Member

    Oct 9, 2012
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    I have searched the web till I drop. Perhaps I do not know how do describe my requirements in a search engine. Here goes, someone may be able to assist me.

    I have an automated gate which is not visible from anywhere in the house.

    The open / close is a single button.

    I do not know if the gate is open or closed without going outside and walking about 20 yards down the drive.

    Once in bed on a cold night, not a great thought!!

    I think I need a magnet on each gate which closes a pair when the gates are closed and is open pair when the gates are open.

    How do I transmit the status back to the house? A cable is a possibility but it is about 60 yards from gate to house.

    Any, any help would be appreciated.
     
  2. hexreader

    Active Member

    Apr 16, 2011
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    82
    How about a battery-driven flashing light at the gates, visible from the house?

    Except - if the gates are electric, which your post implies, then presumably power is already available, so no battery needed - even better.

    Needs a magnet on one gate, then a magnetic switch on the other gate. Available in hobby stores, or maybe even hardware stores. Look for burglar alarm accessories.

    This assumes that you can see the gate from the house (which I guess from your post that you cannot), or that you can see some point near the gate that you could run a wire and a light to.

    It may be that this idea is no good for your situation, but I thought I would suggest the simplest idea first
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    There are a number of RF communication modules that you can buy designed specifically for remote control operations. I haven't personally used them, but I've run across many of them when looking for other things. I suspect there is something out there specifically intended for the kind of remote monitoring that you are talking about. But, if not, then think of how you might use two garage-opener type circuits to do it. You have one in the house and when you press it the circuit at the gate knows it has been asked to tell the house if the gate is open or closed. At this point you have some options, the one at the gate could send back a pulse if the gate is closed and just keep silent if the gate is open. But what if the gate is closed but it doesn't hear the pulse from the house? You get the wrong message (you think the gate is open when it is actually closed). Perhaps this is good enough. But you would rather know that you where heard, so perhaps you have the circuit send two pulses if the gate is closed and only one if the gate is open. Now, if you hear nothing, you know that you don't know what state the gate is in. But what if the receiver at the house only hears one of the two pulses? Then you are back to thinking the gate is open when it is actually closed. So now consider using one of the remotes at the gate that can operate two garage door openers. If it is closed, it generates a pulse to open Door A and if it is closed, it generates a pulse to open Door B. Now, if you hear a pulse, it can't be mistaken for the other state. But you might still miss the pulse and not know anything (but at least you know that you don't know). But you can greatly minimize the chance of this by having it always transmit several pulses, since you only have to receive one of them and it doesn't hurt to receive more than one.
     
  4. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Another (random) thought would be an infrared laser, aimed precisely to point at a receptor attached to your house. The wires could go from the gate to the laser. I'd recommend setting the normal (gate closed) condition of the laser to "off". This way you'll be able to use less power. When the sensor on your house sees the beam, it will know the gate is open. When there is no beam, it means it's closed.

    Okay, so that was my first thought, but there are a few problems--namely, if something comes between the laser and the house and blocks the beam, it will always register as "closed". RF would probably be a better way to go. I'd recommend doing a hack, using wireless garage door openers. You can trigger the remote from the gate, and wire the receiver at your house to turn on a light if the gate is open.

    I guess the real question is, how skilled are you with electronics? Do you know how to read circuit diagrams, figure out what parts of circuit boards do what, etc? Have you ever hacked something? If you're skilled with microcontrollers, you might be able to do it all yourself. Otherwise, a hack would probably be easiest.
     
  5. BJT_user

    Member

    Oct 9, 2011
    35
    8
    My suggestion is, if this gate is for security, why not put a timer on it so it closes on its own after a certain amount of time (5-minutes?) open? That can be accomplished with a time-delay relay.
     
  6. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    That's a good idea. Might be worth looking into!
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    No. There is a safety issue. What happens if the gate closes while someone is in the way?
     
    GeorgeRB likes this.
  8. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Two things you could do--1: A manual emergency kill switch or 2: Infrared beam-break detector that shuts off the motor if something is blocking the beam (i.e. a person half inside the gate).

    Hmm, my brain seems to be stuck on "infrared beams" for some reason..... :p
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    That concern already exists -- he can press the button from the house to close the gate even though he can't see whether the gate is clear or not.

    But it highlights the fact that we need to OP to provide more information. Basically, he is asking for idea on how to design a system to do X without telling use what the desired behavior of the system is. Now, in all fairness, the specific problem that the OP asked for help on is very clearly laid out - I have a gate I can't see and I want to build something that will tell be what state it is in. But, as techies are apt to do, we start looking outside the box for alternative approaches not realizing that we are making a lot of assumptions in the process. Notice that I made an assumption in my suggestions even though I stuck closely to the exact problem that was asked about -- namely, I assumed that it was more important to have positive knowledge that a gate was closed so that lack of knowledge would default to an assumption that the gate was open. But is that what is important.

    If the OP could describe what overall behavior they want, then we can bat around some of these alternative ideas and perhaps find something simple that meets the OP's needs as opposed to the specific problem statement provided.
     
  10. GeorgeRB

    Thread Starter New Member

    Oct 9, 2012
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    A lot of food for thought. Thank you all.
     
  11. GeorgeRB

    Thread Starter New Member

    Oct 9, 2012
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    The gate ahs such a beam in place already. The problem is not knowing what the state of the gate is. It could be
    a) Fully Open
    b) Fully Closed
    c) Partial open / closed

    I need a positive indication that the gate is closed.
     
  12. GeorgeRB

    Thread Starter New Member

    Oct 9, 2012
    4
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    Extra information...

    Mains power at gate can be used.
    Need a positive indication that the gate is closed.
    i.e. LED lit when closed. Off at all other times.

    Beam across gate already in place to stop motor is broken.
    (i.e. Gate could be partial open / closed.
     
  13. vortmax

    Member

    Oct 10, 2012
    103
    18
    Depends on how involved you want to make this....

    My first thought would be a magnetic reed switch like you mentioned or a limit switch mounted along the hinge. You could also go fancy with some sort of linear rheostat on the actuator tied into an ATD so you could read out the exact position of the gate and not just open or closed. Any/all of these would be tied to the digital IO pins on a micro.

    Now the two options I can think of here would be a small device with a TCP stack and wireless connection attached to your home network. Then you could poll over a telnet connection or if you are really handy, implement snmp. Something like a wireless version of this: http://www.itwatchdogs.com/product-detail-watchdog_15-71.html with the door sensor.

    option two would be something based off the TI CC1111 chip which does sub-gigahertz comm. Use the same door switch to drive one of the DIO pins to either toggle the RF on or off, or have it constantly transmitting the door position. Then have another similar base station (same chip) in the house listening for the link that drives an LED or some other indicator to tell you the gate is closed.

    Of course, both are massive overkill, but I would feel bad if they weren't.

    the motor should already also have some sort of overload switch or other safety to prevent it from squishing someone....I can't see that being a needed addition to this project....although a 'gate opening/closing' indicator would be pretty simple to add.
     
    Last edited: Oct 10, 2012
  14. PRFGADGET

    Active Member

    Aug 8, 2011
    51
    7
    60 yards is a fairly long haul for a low voltage control circuit ( not overly long but getting out there).
    Is there a interface / junction box at the house that the push button actually operates ?
    If so there is a possibility of slaving open / close indication at that point.
    more information might be helpful.
     
  15. vortmax

    Member

    Oct 10, 2012
    103
    18
    My bad. I read feet, not yards.

    They have those cheap Ethernet over power units. So if you have mains power , you can extend wired Ethernet without running new lines. A cheap access point and can-tenna could probably pull it off too
     
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