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555 timer and speaker

Discussion in 'General Electronics Discussion' started by dcac, Mar 18, 2014.

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  1. dcac

    dcac

    56
    1
    Jul 10, 2013
    Hi there, I am trying to get a sound from a speaker witch is connnected to 555 timer.
    Some parameters: speaker 8 Ohms,0.25W; 555 timer 50 hz output.

    I can't get a sound from a speaker when i connect to the 555 (astable mode). I read that a capacitor in series have to be with the speaker. Could you tell me what is the function of the capacitor in here? And how to determine the value of capacitor for the speaker.
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    The capacitor is to block the DC portion of the signal and allow the speaker cone to move in both directions from its rest position. If your 555 is oscillating, you will get a sound from the speaker either with or without a capacitor, though it may be more distorted without the capacitor. 220uF should work.

    Show us your circuit.

    IXP
     
  3. cjdelphi

    cjdelphi

    1,096
    104
    Oct 26, 2011
    I've never bothered with a cap in series from a 555 as it should be a clean on/off signal...
     
  4. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    Can the 555 timer drive such a low impedance without some sort of buffer. I also agree that a cap should not be used if you want a clean signal otherwise you would need such a large capacitor to increase the time constant to allow a clean signal.

    Adam
     
  5. dcac

    dcac

    56
    1
    Jul 10, 2013
    I have found out the reason why the speaker did not play any sound. It seems that the 555 timer can output up to 200mA and not capable of driving the load witch asks more than 200mA. In this case the load would require 5v/8Ohms=625mA. That would be 3 times more than 555 can give. So when I put a resistor in series with the speaker it workds fine.
     
  6. cjdelphi

    cjdelphi

    1,096
    104
    Oct 26, 2011
    You need a transistor on the output of pin 3.
     
  7. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    Good glad you found out what it was.
    Adam
     
  8. peter.rabbit

    peter.rabbit

    11
    0
    Mar 16, 2014
    +1

    I'm surprised you didn't kill the timer..... :)
    I've killed many 555's, usually accidentally direct earthing pin 3....
     
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