Starting a project - Transistor problems

Discussion in 'The Projects Forum' started by Excizted, Nov 20, 2009.

  1. Excizted

    Thread Starter New Member

    Nov 20, 2009
    4
    0
    Hello all. I've just started my first real electronic project, and therefore I've come to this forum :)

    I'm trying to achieve volume controlling from an Arduino for an external sound device, and I've been searching like a mad man.

    What I guessed would be the easiest way to do this was to use a transistor and wire my sound source, sound destination and a analog output from the Arduino.

    This does not work as it is supposed to. When I send analog signal 255 (max of 5v Arduino) the sound start flowing, but when decreasing it to 180 I'm not able to hear any lower in the sound. I guess I'd just turrn it more down, but anything under 150 simply means no sound at all.

    What could I be doing wrong, and is it at all the right way to go trying to manage volume from a second signal?

    Thanks,
    Excizted :)
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Post a schematic of what you have now.

    It's necessary to have a schematic to provide a starting place; and then make a plan for how to get from where you are, to where you want to be.
     
  3. Excizted

    Thread Starter New Member

    Nov 20, 2009
    4
    0
    A schematic to consist of what? ;/
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    A schematic of the circuit that you connected to the Arduino, of course.
     
  5. Excizted

    Thread Starter New Member

    Nov 20, 2009
    4
    0
    The transistor I am using:
    http://www.sparkfun.com/datasheets/Components/BC546.pdf

    I've got:
    Sound Out + and -.
    Sound Speakers + and -.
    Arduino Analog Out +, no minus/gnd since the sound and arduino shares ground.

    To the Collecter I wired up my Sound Out +.
    To the Emitter I wired up my Sound Speaker +.
    To the Base I wire the Arduino Analog Out.

    The Sound Out minus and Sound Speaker minus are connected directly to each other.
     
  6. spacewrench

    Member

    Oct 5, 2009
    58
    1
    If this (attached) is what you mean, I'm gonna go ahead and say it's probably not gonna work very well. A voltage-controlled amplifier is a pretty complex circuit, as you'll see from some of the links. You can get a monolithic IC to do it, but many of them are expensive, and you may need special power supplies (positive & negative, at least) and/or special interface circuitry.
     
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  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    You are trying to use a low power DC transistor as a high power AC variable resistor.
    They are completely different.

    If your Sound Speaker has an amplifier inside then you can use a Jfet and a few resistors and capacitors to control its volume.

    A TDA7052A little power amplifier IC (0.88W at clipping into an 8 ohm speaker with a 6V supply) has a DC volume control built-in.
     
  8. Excizted

    Thread Starter New Member

    Nov 20, 2009
    4
    0
    Ok then. I thought a transistor would do, since thats what a friend told me.

    What would be the best components to control volume of several speakers with an Arduino then?
     
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