Magnetic Reed Switches to Unlock Door

Discussion in 'The Projects Forum' started by dan838792, Mar 26, 2007.

  1. dan838792

    Thread Starter New Member

    Mar 26, 2007
    2
    0
    Hello everyone. This is my first post. In browsing around a bit today I thought that this community would be a good place to ask a question (or two) about a project I've been dreaming up for a while now.

    For a bit of background, my only experience with circuits (besides minor home repairs) is from a couple of under-grad classes I had to take as part of my mechanical engineering degree. In other words, I know enough to recognize a term or two, and as far as I know, Ohm's Law can solve every problem know to man about electricity.

    So, here's what I've dreamed up...

    I want to build a secret door to the space under our stairs. After watching a show on HGTV, I've gotten a bug to use magnets as keys to unlock the door. I've attached a pdf of the simple circuit I've come up with. Basically S1 would be a magnetic switch in the door to turn everything off if the door is open. S2 is a normally closed switch that could be opened up to re-set the circuit. S3 is some sort of switch to turn the circuit off if it is left on too long. Step one would be triggering reed switch S4 with a magnet. This would open up the first transistor (R2 would keep the circuit from frying). Then S5 would be triggered (again with a magnet) to turn the solenoid on which would unlatch the door. Once the door is unlatched S1 would open up, turning off the circuit.

    So, my questions are: is this a practical and workable circuit? If not, what would you recommend for something like this? What could I use for S3? I was thinking a thermal switch (replaced one in a blender once, boy did that prove the little missus wrong for once!) Or would some sort of timer be easier/more reliable?

    Thanks for any help you can offer!

    Dan
     
  2. kender

    Senior Member

    Jan 17, 2007
    263
    0
    What were you thoughts about the thermal switch? Were you going to use a thermal lag to make a delay? This sounds like a neat idea, although I've never seen anyone actually use this approach to make a delay.

    It's common to use 555 timer in one-shot configureation for delay switch. For example, see the 3rd circuit from the bottom here http://ourworld.compuserve.com/homepages/Bill_Bowden/page9.htm
    Googling "555 one shot" will bring up lots of schematics.
     
  3. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    Have you considered a magnetic mechanical solution?

    Each has a lever that will either engage or disengage based on where you put the a magnet. Eight positions could be 'programmed' thus
    Latch = 0 and Unlach = 1

    A magnet on a latch postion causes the lever to latch, a magnet on an unlatch postion cause the lever to unlatch. I chose 1 for unlach as it takes 1 magnet.

    So 10111001 would require five magnets to unlock the door but if you put a magnet where a zero is the lever latches.

    You can make it more complex by using magnets on the levers in such a way that the wrong polarity effects them.

    The magnets can control switches and a solenoid "bolt" without one bit of semiconductor material. I leave it to you to figure that one out. :)
     
  4. Gadget

    Distinguished Member

    Jan 10, 2006
    613
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    One of our local suppliers had a kitset RFID setup designed just for this sorta thing...... if you wanted to use a small RFID tag, or RFID credit card and wave it across the pickup.
    I have one set up on the Cat door at home, as those magnetic ones where useless when the neighbours cat also has a magnet on its collar.
    Now the cat has a uniquely coded RFID tag in its collar, and can come and go as she pleases locking all other cats out.
     
  5. lil1also

    New Member

    Feb 20, 2011
    1
    0
    Going to try to help install a hidden door bookcase in my parent's home for them. I'm a newbie, but would like to use a chess board on the bookcase, and when you move a certain chess piece to a certain spot, the door would open. How could I approach this? Hidden magnet under chess piece or chess board? :confused:
    What kind of materials would you recommend using? For a latch?
    Could you please also explain how I could make it safe for anyone in the room, to not to be stuck inside. A failsafe in case of power failure etc.?
    I have a college degree :eek:, but not in electrical anything, could you please try to describe in the simplest terms possible :)
    Thanks in advance to anyone who takes the time to respond!
     
  6. kender

    Senior Member

    Jan 17, 2007
    263
    0
    On the inside, have a handle (or a push-plate, depending which way the door opens) which is connected to the latch mechanically.

    P.S. Mechanical design and carpentry - not electronics - are the tough part of this project, if you want to do it right You can try various electronics designs even in the late stage of the project.
     
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