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Arc via pwm circuit (arduino)

  1. Dec 16, 2011 #1
    Hello everyone. My first post so bear with me.

    I'm planning on buliding an arcgenerator (and possibly an arc speaker later on if this works) with my arduino and a coil. I'm relatively to electrical engineering, so there are a few things I need some help with.

    If i've understood things correct, when there is a change of a surrounding magnetic field around a coil, power is induced in the coil. And the output U from the coil is depending on the ratio between the primary and secondary coil.

    So with the help of my arduino, I will have a PWM out connected to a transistor, which is connected to a coil (similar to an ignition coil in a car), and the voltage will amplify while the current will decrease.

    Here's a drawing:

    http://imageshack.us/photo/my-images/861/ritning.jpg/

    (sorry for my poor circuit drawing skills...)

    So my questions are:

    * Is this even possible? Am I thinking right?

    * Will my arduino board be affected by the amplified voltage? (In other words, will it be damaged?

    * Are there any other components that should be included? Resistors, voltage dividers etc...

    * How will the amount of turns on the coil affect the outcome? 10turns/20turns have the same ratio as 100turns/200turns, but I have a feeling the outcome won't be the same?

    Thanks!

    /D
     
    Last edited: Dec 16, 2011
  2. jcsd
  3. Dec 16, 2011 #2
    About 30 years ago I played around with ignition coils in an attempt to do what you want to do. As I recall, the highest voltage I could generate was about 1000 volts. I wanted to generate 10s of kilovolts.

    This is why I don't think it worked. The coil that I had, had a primary resistance of about 1 ohm. In it's normal application I believe a switch provided a direct short through that 1 ohm to the battery, for only an instant. During that instant, a large current flowed through the coil and created a substantial magnetic field. When the switch opened, a high voltage (much higher than 12 volts) was developed across the primary and a much higher voltage yet was developed across the secondary. The voltage I could feed into the primary was far less than the voltage created by the current. Have you tried to input a signal into the coil and measure what your output voltage is?

    Besides that, you need to interchange the battery with the coil.
    I would use an opto-isolator between the arduino and the transistor.
     
  4. Dec 16, 2011 #3
    Many thanks for reply skeptic!

    I haven't made my coil yet actually, need to figure out how I want the ratio between the turns of the coils.

    About the optoisolator, interesting component. However, the ones I could find had too much delay between the switch, the shortest I could find was about 6 ms. My pwm-signals will be shorter than that. So you're saying that the arduino circuit will be affected by the voltage from the coil circuit?

    And btw, I also played around with a ignition coil a couple of years ago, with a car battery, and it produced a nice spark whenever you connected it. (not a continous spark though)
     
  5. Dec 16, 2011 #4
    Any time you work with voltages that can arc you want to thoroughly protect delicate and expensive electronics. Arcs can find all sorts of unintended paths and can back to your Arduino easier than you can imagine. The first opto-isolator I could find was this one. Does it look like it would work?

    http://www.ti.com/lit/an/slva229/slva229.pdf

    For the transistor that drives the coil, I would use a power transistor or even a mosfet. Also the more power you can feed the primary, the more you'll get out.
     
  6. Dec 16, 2011 #5
    Yeah you're probably right. Also found a similar optoisolator on a swedish site (Im swedish), so thanks! The switch delay was low enough. But with the optoisolator, do I really need a transistor? The way I see it, the optoisolator is a kind of a transistor, right?
     
  7. Dec 17, 2011 #6
    An opto-isolator is really nothing more than a LED driving a light sensitive semiconductor. Besides opto-coupled transistors I've seen opto-coupled scrs, triacs, fets, and photodiodes. The photdiodes are worth mentioning because they have the highest frequency response but the lowest gains. If you decide to use one you would have to amplify its output.
     
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