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Timed on/off switch

Discussion in 'Electronic Basics' started by [email protected], Mar 22, 2007.

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  1. Guest

    Hi, this is my first post here, and I looking for either a component
    or a circuit design for a special project I am doing.

    Basically I need a component that switches the current running through
    it on and off at a frequency of about 1-6 Hz.

    I am fairly apt at soldering a general circuitry so any suggestions
    would be great!

  2. Greg Neill

    Greg Neill Guest

    AC or DC current?
    How much current?
    What voltage?
    What is your power supply voltage?
  3. Guest

    It will be a DC system running at 12V. It will be carrying close to 3
    amps at max. It will be getting the power from a AC-DC converter
    plugged into the wall. The load will be a electromagnet.
  4. What purpose is there in cycling such a magnet at 6 Hz?
  5. Guest

    Well, I guess that 6 is a little high... maybe around 2 Hz will be
    optimal. I am trying to make my own unique design for a tattoo gun I
    am making.
  6. Guest

  7. John Fields

    John Fields Guest

    View in Courier:

    .. | | |
    .. | | +-------+
    .. [1000] +---------+ | |K |
    .. | 7|_ |8 | [DIODE] [COIL]
    .. +------------O|D Vcc|--+ | |
    .. | 6| _|4 | +-------+
    .. [82K] +-----+--|TH R|O-+ IRL3303 |
    .. | | | 2|__ |3 | \ C
    .. +->[500K] +-O|TR OUT|--|-------------+----B
    .. | | | GND | | |K E
    .. +----+ +----+----+ +------+ | |
    .. | 1| 555 |+ | [1N4744] |
    .. [0.68µF] | [10µF][100nF] | |
    .. | | | | | |

    The 10µF electrolytic and 100nF ceramic capacitors are to be mounted
    directly across pins 1 and 8 of the timer.

    The 0.68µF capacitor is polyester film (Mylar).

    With the 500k rheostat at minimum resistance the output frequency
    will be about 6Hz and at maximum resistance the output frequency
    will be at about 1Hz.
  8. Guest

    Wow, thanks guys!
  9. Look at and search for the buzzer demo. That's basically
    how to do this.
  10. Rich Grise

    Rich Grise Guest

    Yes, it's called a transistor. But I'd put it in the negative lead
    (your white one), and call the negative output of the supply "ground";
    it makes the control circuitry simpler to design, because then it can
    all be referenced to ground.

    You need something to generate the pulses, like a 555 or astable
    multivibrator, and the output of that will switch the transistor on
    and off. You'll also need a "catch" diode, which is a diode in
    parallel with the coil, that absorbs the inductive spike when
    the current is turned off. Some might recommend a MOSFET - for
    something on this order of complexity (which isn't very much,
    for an old fart, albeit for a newbie it can be daunting), it's pretty
    much a matter of personal taste.

    Do you have any electronics experience at all? If not, I'd recommend
    searching the web for tutorials and such so you have a handle on what
    you're trying to accomplish, and how to go about doing it.

    Good Luck!
  11. John Fields

    John Fields Guest

  12. Guest

    This whole thread has been a great help! As for my electronics
    background... I am a level 2 electrician apprentice... Although this
    doesn't help much as far as experience on low voltage DC systems, I
    understand everything that has been discussed here and have a good
    grasp on electrical flow and I can solder well.

    Now one thing I am unclear about (this may sound like a stupid
    question)... If I am looking at an electrical circuit diagram and it
    leads a few parts to the ground symbol... do I just connect it to the
    box I'll be putting it all in?
  13. Rich Grise

    Rich Grise Guest

    Only if the box is metal. :)

    And, one of the conventions in sci.electronics.basics is that there is
    no such thing as a stupid question, unless you ask the same one three or
    four or five or ten times, trying to get the answer you think you want
    instead of the right one (of which there are usually several). :)

    If you really want to set the world on fire, invent a tattoo eraser
    that's as cheap to have done as having the tattoo installed in the first
    place. :)

    Have Fun!
  14. You can generally find the US Army or Navy instruction books online. They
    are a very good starting point for learning since they have been used many
    many times for teaching these subjects.
    You can. Or you can just connect all of the ground connections together. The
    notion of ground is a conceptual one - it really means common return to the
    power supply, sometimes with an element of shielding associated with it.
  15. Guest

    Okay... I think I found the circuit I am going to try to assemble... I
    am confident that I can do it:

    But the load of course won't be a light, rather an electromagnet...
    and I will connect a MOSFET in parallel with the electromagnet to
    avoid the damages of any current spikes. What do you guys think?

    As for a tattoo eraser... I'll worry about building one of those when
    I start having kids :)

  16. Be aware that the coil / stylus assembly will have a mechanical resonance of
    some sort. Syncing your driver to this will be less than fun.

    That's why most every unit you can find just uses a set of point which break
    the current at max forward position.
  17. Guest

    Another thing I might just want to throw out there is that I am also
    looking for other ways of preforming this operation. Basically what I
    want to happen is:

    1. Electromagnet energizes
    2. Electromagnet attracts permanent magnet
    3. Electromagnet denergizes
    3. Permanent magnet get pushed away by the spring

    And all off this to repeat at about 1-3hz...

    Using a 555 timer in a strobe light circuit is the best I can think of
    at the moment.

    I am also using this project to gain experience in the electronics

    All of your suggestions so far have been great!
  18. ehsjr

    ehsjr Guest

    Something like this should do it for you:

    +12 ---+------------------------------------+
    |a |
    [D1] |
    | |
    +----+--------+---+ |
    | | | | +----+
    | [1K] --------- | |
    | | | 8 4 | | |
    | +-----|7 | [100K] |
    | | | | | |
    | [33K] | 555 | | |-+s
    | | | 3|---[330R]-+-,| STP12PF06
    | +-----|6 | g||-+d
    [100uF] | | | |
    | +-----|2 | +----------+
    | | | 5 1 | | |
    | |+ --------- | |
    | [10uF] | | [Electromagnet] [D2]
    | | [.1uF] | | |a
    | | | | | |
    Gnd ---+----+--------+---+------------------+----------+

    D1, D2 = 1N5404

    With the values shown, the 555 should give you about
    2 seconds on, 2 seconds off. Use a regular NE555, not
    the cmos TLC555 version.

  19. Guest

    Thanks Ed, that actually looks a lot simpler than the one I planned on
    using (and a bit more applicable)... A few questions: What type of
    diodes should I use? and what components should I change if I wanted
    to increase the frequency slightly? Could I add a rheostat anywhere?
    2s on and 2s is a bit too slow, I think.
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