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Garage sensor: How do they work ?

Discussion in 'Electronic Design' started by Rodo, May 21, 2005.

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  1. Rodo

    Rodo Guest

    Hi all,

    I want to make a circuit that will beep (or something like that) for when I
    have the garage door semi-open. Since the system already has sensor in it, I
    figure I can just interface to them.

    I measure the terminals of the two sensors that stop the door from closing
    when interrupted. One shows a 12vdc and the other a 3.6vdc. If I place an
    object in the path, the 12vdc goes to 13.6vdc. The other does not change.
    How do these things work ?

    I figure one is an IR Tx and the other Rx. The beam is interrupted and the
    voltage changes (and the LED on it blinks), right ? I measure no AC or
    frequency from any of the two sensors ( at any time).

    I'm planning to use a PIC18. I'm just puzzled by the 1.6v difference ? Is
    that all that they use ?


    BTW the motor is a Genie unit (belt driven ...very quite kind).
  2. Dave

    Dave Guest

    If you do this your beeper will only sound when there is an obstruction
    between the sensors. The door can be opened without the obstruction
    sensors activated (my door will stop when button is pressed when
    I use a reed switch and magnet to sense if the door is not closed. I
    made my own (I'm cheap) from junk parts but they can be purchased from
    Radio Shack in N/O or N/C types.
  3. Jim Thompson

    Jim Thompson Guest

    I have RF-linked tilt switches on my doors (Chamberlain/Liftmaster)
    and the receiver plugged into an outlet in my office.

    ...Jim Thompson
  4. Joerg

    Joerg Guest

    Hello Rodo,

    As Dave said, the obstruction sensors won't help you here. I do not know
    belt drives but figure they must have something similar to what our
    screw drive has at either end: End switches. These are simple mechanical
    switches and the one near the door closes (or opens, depending on model)
    when the door is fully closed.

    Regards, Joerg
  5. Richard H.

    Richard H. Guest

    As others have commented, these won't tell you if the door is opened

    This type of sensor is designed to be floor-mounted (can be driven over)
    and will trip the circuit if the door is opened more than an inch or so
    - see Overhead Door Contacts:

    Here's a cheap wireless package that you could use as a starting point:

    Or, you could just get a standard magnetic door sensor, mount it
    anywhere on the vertical edge of the door when it's closed, and it'll
    trip when the door opens.

  6. Jim Thompson

    Jim Thompson Guest

    Is it a segmented-panel door? If so put the tilt switch on the
    topmost panel.

    ...Jim Thompson
  7. Guest

    As has been said, a burglar-alarm magnetic switch is pretty easy. Also,
    if the motor unit has a light on it, and the light doesn't go out after
    the door has been open for a while, you might be able to use something
    like a cheap wall-wart plugged into the light socket to give you a
    signal when the door is open.

    Matt Roberds
  8. Rich Grise

    Rich Grise Guest

    Of course they do. If the "closed" switch isn't giving its "door closed"
    signal, then the door isn't closed. And if the switch at the top of the
    travel isn't giving its "the door is fully opened" signal, then the door
    is obviously someplace in between, which is what Rodo was asking for, as
    far as I can tell.

    The elecronics comes into play when you decide to sense the state of both
    limit switches simultaneously. That's an "AND" gate.

  9. Joerg

    Joerg Guest

    Hello Jim,
    But the top panel moves...

    Regards, Joerg
  10. Joerg

    Joerg Guest

    Hello Rich,
    The Genie units usually have that already in them, along with another
    "one bit memory" that tells them in which direction the door had moved last.

    Regards, Joerg
  11. Rich Grise

    Rich Grise Guest

    Uh, yeah, that's kinda the point, which would be obvious if whoever
    Joerg is responding to hadn't snipped everything.

    Let's start plonking googlekiddies.

  12. Joerg

    Joerg Guest

    Hello Rich,
    Well, top panel mount would really only leave a wireless solution with
    batteries. A few hot weeks like out here right now and the batteries are
    toast. Garage door panels can become so hot that even a brief touch with
    a finger leaves a blister.

    Seems overkill to me since the usual door drive already has two end
    switches. On our system (Genie screw drive) you could buy or make a
    spare set of end switches and mount them on the other side of the track
    if you wanted to have a completely isolated setup. If they are wired so
    they close when the door moves away from the end point they could simply
    be hooked up in series with a lamp or whatever to indicated a door that
    was left open. No electronics required. Anything mounted to the door
    itself is likely to get banged up.

    Regards, Joerg
  13. Jim Thompson

    Jim Thompson Guest

    Hmmmm? My doors have about 1" of some kind of insulation between the
    metal panels.

    ...Jim Thompson
  14. Joerg

    Joerg Guest

    Hello Jim,
    You must live in a pretty new house then or have newer doors. Ours are
    top quality but 30+ years old. Almost undentable metal but insulation or
    even double walled? Nope. When someone touches or accidentally leans
    against the inside of such a door on a hot summer day you'll hear a
    "tsssst", then an expletive, followed by an involuntary tarantella dance.

    Regards, Joerg
  15. Jim Thompson

    Jim Thompson Guest

    11 year old house.

    ...Jim Thompson
  16. Joerg

    Joerg Guest

    Hello Jim,
    Then you do have a new house. Ours was built in 1970. Good quality stuff
    so most of the original hardware is still in place.

    I grew up in Europe where a building under 50 years is considered quite
    new. The Romans probably thought more along the lines of 400-500 years.

    Regards, Joerg
  17. Rodo

    Rodo Guest

    Hmmm. I guess I didn't make myself too clear on this one :). I'm not
    interested in the state of the door. I know the door will be open
    (slightly) because I opened it. I just want to have something beep if a
    critter (or not so critter) comes into the garage. My condo sits on top of
    the garage and I just want to cool it down on summer days by leaving the
    door open a bit. It is also not intended to be open overnight.

  18. Original requirement:
    "I want to make a circuit that will beep (or something like that) for
    when I have the garage door semi-open."

    Re-stated requirement:
    "I just want to have something beep if a critter (or not so critter)
    comes into the garage."

    Glad I didn't attempt to contribute earlier! 13 replies so far, all
    based on your misleading spec.

    What size of critter must be detected? (Mouse, rat, cat, squirrel,
    Alsatian, neighbour's baby, teenage vandal, 300 lb escaped

    Begging answers to those, I'd be thinking along the lines of either an
    interrupted IR beam or adapting a proximity detector (PIR).
  19. Guy Macon

    Guy Macon Guest

    Go out and buy a standard electric cattle fence and mount a couple of
    isulators so that you can string a wire across the opening a few inches
    above the floor. No human intervention needed, and no need to move a
    signal from the garage to the house.
  20. Rich Grise

    Rich Grise Guest

    Wouldn't that make it a little inconvenient to drive in or out? ;-)

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