RadioShack 8ohm speaker circuit

Discussion in 'General Electronics Chat' started by kingArgon, Mar 12, 2013.

  1. kingArgon

    Thread Starter Member

    Mar 20, 2011
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    So I got one of these cheap Radio shack speakers and im interfacing it to a ADC on a microcontroller. The speaker is rated for .2 watts max. How do I hook this thing up without frying it? Someone mentioned hooking it up in series with a current limiting resistor would work. Is this true?
     
  2. MrChips

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    Oct 2, 2009
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    From your post one assumes that the speaker impedance is 8Ω and you are connecting this to the output of an ADC to produce sound.

    This will not work. The output of the ADC does not have enough power to drive a loudspeaker. The output impedance of the ADC is much greater than 8Ω. You need to use an audio amplifier, something like an LM386.
     
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  3. #12

    Expert

    Nov 30, 2010
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    You're looking at less than a thousandth of a watt of power.
    You need an audio amplifier.

    Edit: simultaneous posts, each saying the same thing.
     
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  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I drive that little RS speaker in this project. It makes a beep and a boop so the user knows what's going on.

    Just a transistor (fet?) and a resistor to drive it. You may want to play with the resistor value some, I had a 12V source available on this job.
     
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  5. Ron H

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    An ADC does not have an analog output. Perhaps you meant to say DAC?
     
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  6. MrChips

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    Good eye! We all missed that.
     
  7. kingArgon

    Thread Starter Member

    Mar 20, 2011
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    Thankyou everyone who responded on this thread! Let me clarify!

    I was researching using a piezo speaker as vibration measurement tool but i dont think this radioshack speaker is piezo.

    I really just wanted to know how to hook the little guy up for either vibration measurement(adc) or PWM/DAC sound generation through the uC.
     
  8. kingArgon

    Thread Starter Member

    Mar 20, 2011
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    ErnieM, In your circuit i calculated a current of .5mA on the speaker.

    I = V/R => I = 12Volts/22008Ohms => .54mA

    is this right?
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    A piezo element, rather than a piezo buzzer, can be driven from the output, barely. These are the raw discs, no buzzer circuitry added. You can scavenge a free one from a musical greeting card or similar.
     
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  10. MrChips

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    Ok, it's back to square one.

    Lesson #1 - when posting a question, make sure you tell us everything you are attempting to do.

    You are mixing up two questions in one.

    Are you attempting to build a vibration sensor?

    Or are you attempting to create sound via a loudspeaker from a microcontroller?
     
  11. kingArgon

    Thread Starter Member

    Mar 20, 2011
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    my original question is how to hook up this speaker appropriately without blowing it. ErnieM, gave a good schematic but i am not sure what the current is across the speaker. i calcululated .5mA of current and 6mW of power.


    Side note: I'm just learning that this speaker IS NOT piezo and cant be used with the adc. So now im going to use it with the DAC module or the PWM module of the uC.
     
  12. MrChips

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    Ok. What are you connecting the 8Ω speaker to? What do you want to happen to the 8Ω speaker?

    Forget the Side note for now because it makes no sense and only confuses the issue.
     
  13. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Use the PWM or just a port pin. You are giving it a square wave to make a tone.

    If your PIC is fast enough and has a large supply of memory you actually can drive the PWM with .wav file data and get music.
     
  14. kingArgon

    Thread Starter Member

    Mar 20, 2011
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    The speaker needs to be hooked up in series to the uC pin(5volts). What size, if any, resistor should i use to limit the current to the speaker?
     
  15. #12

    Expert

    Nov 30, 2010
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    The idea is not to protect the speaker, it is to protect the micro-controller. For that, we need you to define the controller.
     
  16. kingArgon

    Thread Starter Member

    Mar 20, 2011
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    it is a PIC16f877a uC
     
  17. #12

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    That chip shows 25 ma in or out on its pins.
    If you're using 5 volts, R=E/I
    5/.025 = 200 ohms minimum to protect the chip.
    If you are using 3 volts or 3.3 volts, I have given you the math to figure it out.
     
  18. MrChips

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    You still have not said what do you want to do with the speaker?
    Or what do you expect the speaker to do?

    #12 is correct. You are not protecting the speaker. You want to protect the chip from burn out.
    8Ω at a chip output is like a short circuit to GND.
     
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  19. kingArgon

    Thread Starter Member

    Mar 20, 2011
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    The purpose of the speaker is just to experiment with. I want to input a PWM signal and i just want to find a resistor to protect the speaker.

    #12, i calculated that to protect the speaker i which is max 200mW, that i should use a resistor of 200 ohms. 5v/25mA = 200 ohm. This would make the max wattage on the uC output = 125mW.

    is this a correct assumption?
     
    Last edited: Mar 15, 2013
  20. MrChips

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    Ok. I give up. Here we are trying to help you and all you can respond with is I'm just experimenting.
     
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