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Cigar Box

Discussion in 'Electronic Basics' started by [email protected], Jul 2, 2005.

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  1. Guest

    Hi, I would like to make a cigar box with an electric opening and
    closing lid. I would like to have a button on the outside to open the
    lid and another button on the inside to close it. The mechanical part I
    can easily make but the electronic circut I cannot. I have a variety of
    small dc motors I can use. Can anyone help me with the circut?

    Thanks, Raul
     
  2. Chris

    Chris Guest

    Hi, Raul. The easiest way to get a motor to open, then close a lid is
    to put a cam on the shaft of the motor, then make a lever and roller
    such that the rising of the cam causes the lid to open, and when the
    cam turns and its radius becopmes less, to close. That requires a
    geared DC motor that will take a couple of seconds per revolution. The
    big advantage of this is that you don't have to worry about reversing
    the motor. If you've got that kind of a motor, then you might be able
    to accomplish the following simple circuit, which will let you do what
    you want.

    In addition to your two pushbuttons, you'll need a means to tell if the
    lid is fully open or fully closed, to stop the motor. This can be done
    by getting a couple of small press fit magnet switches. These are
    available as All Electronics P/N MS-11, for $2.25 USD per set. You'll
    need two sets. These normally closed switches will open when the
    matching magnet is in proximity. Place two of the switches facing
    opposite sides of the cam, and put one magnet on the cam itself such
    that, when the lid is fully open or fully closed, the magnet is in
    front of the appropriate switch.

    What you do next will depend on the motor you've chosen, specifically
    its voltage and the current draw while it's on. Assuming you've got a
    3VDC motor that draws half an amp or less (you can scrounge something
    like this from any number of small battery eater kids' toys), you can
    do something like this (view in fixed font or M$ Notepad):

    ` PB1
    ` T
    ` ---
    ` .--------o o-------------o----------o----------.
    ` | | | |
    ` | PB2 | | |
    ` | T | | |
    ` | --- | | |
    ` o--------o o-------------o | D1|
    ` | | / \ -
    ` | | ( M ) ^
    ` | | \_/ |
    ` | SW1 SW2 | | |
    ` o-------o o----o o---' | |
    ` | \--- \--- | o----------'
    ` | .-. |
    ` | | | |
    ` | 47 ohms| | |
    ` +| '-' |
    ` --- | |/
    ` 3V - o--------| Q1
    ` | | |>
    ` . .-. |
    ` | 1K ohm | | |
    ` | | | |
    ` | '-' |
    ` | | |
    ` -------------------------o----------'
    (created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)


    Other components shown above are Q1, an NPN power transistor (All
    Electronics P/N TIP29C, $0.60 USD ea.), D1, a 1 amp rectifier diode
    (A-E P/N 1N4001) and a 47 and 1K ohm resistor (available in packs of
    10ea. for USD $0.50 from the same source). By the way, they also have
    a wide selection of normally open pushbuttons, if you need a couple of
    those. One inexpensive choice would be their MPB-1 SPST momentary red
    mini-pushbuttons for $0.35 ea.)

    Here's how the above circuit works: At rest, the motor cam magnet is
    over one of the normally closed switches SW1 or SW2, so no current is
    flowing there (the switches are in series). Neither pushbutton PB1 or
    PB2 are being pressed, so no current is going to the base of the NPN
    transistor Q1 from any source. That keeps Q1 and the motor M off. But
    when you press either pushbutton, current will flow through that switch
    and the 47 ohm resistor to inject about 50mA into the base of Q1, which
    will turn Q1 ON, allowing current to flow through the motor and turn it
    on. As the cam and the magnet moves off the magnet switch, it will
    close. That will allow current to continue flowing into the base of
    the transistor through the two series magnet switches, keeping the
    motor on. It will stay on until the cam moves the magnet over to the
    other magnet switch. That will interrupt the base current, turning off
    Q1 and the motor until another pushbutton is pressed.

    The 1K ohm resistor from the base of Q1 to GND helps ensure the
    transistor Q1 will really be off when there's no current through the 47
    ohm resistor. It's optional, but recommended (as it reduces leakage
    current when the transistor is off, which will make your batteries last
    longer). The diode D1 is necessary to prevent the inductive kick of
    the motor from destroying the transistor when it tries to turn off.

    The idiosyncracy of this setup is that either switch can make the lid
    open or close. Unless there's somebody lurking inside the cigar box,
    there shouldn't be a problem with that switch. So, if you can live
    with having the outside switch having the capability to open or close
    the lid, this will solve your problem. Look at it this way -- "It's
    not a bug -- it's a feature!" ;-)

    The above example is for a small 3VDC gearmotor scrounged from a kid's
    toy. If you've got room in the cigar box, you should use C or D
    batteries for this. Half an amp is too big a load for two AA
    batteries, but if the motor is smaller and you're not planning on many
    cycles, you might be able to get away with AAs. But if your motor has
    another voltage or a higher current, you might want to post back with
    your specs. There are some limitations to the above circuit, and
    you'll probably at lest want to change resistor values. If your motor
    is more than 4.5V, it might be better to use a MOSFET for a higher
    current motor.

    If you need battery holders or other components, you might want to go
    to the All Electronics website:

    http://www.allelectronics.com/

    By the way, while you're there, sign up for their free catalog. They
    have a lot of good stuff for projects like this.

    I hope this has been of use. If it doesn't work for you, please post
    again with more information and your requirements.

    Good luck
    Chris
     
  3. Guest

    Thanks, if I get it to work I'll post some pics.
    Thanks again.
    Raul
     
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