+ Post New Thread
Results 1 to 11 of 11
  1. #1
    Full Member level 6
    Points: 1,509, Level: 8

    Join Date
    May 2014
    Posts
    379
    Helped
    1 / 1
    Points
    1,509
    Level
    8

    What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    Hello,


    This circuit works as a light detector,
    once there is light fallen on the LDR, the speaker buzzes

    But, when connection this speaker alone, and supplying a voltage across its terminals, no sound is obtained. contrary to the buzzer, that once supplied, a sound occurs.

    what is the difference between a speaker and a buzzer, why to choose a buzzer in this circuit, and why this speaker make no noise once supplied?

    - - - Updated - - -

    This is the circuit

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 53,693, Level: 56
    Achievements:
    7 years registered
    Audioguru's Avatar
    Join Date
    Jan 2008
    Location
    Toronto area of Canada
    Posts
    8,747
    Helped
    2051 / 2051
    Points
    53,693
    Level
    56

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    EDIT:

    A piezo beeper is a piezo transducer with a transistor oscillator inside.
    The transducer beeps when the oscillator is powered by a DC voltage.

    The output of the 555 produces a buzzing tone when there is light.
    The 555 in the circuit is overloaded by most low impedance speakers, it should have a resistor in series with the speaker to limit its current to 200mA.

    A piezo beeper might not beep when fed the buzzing tone from the 555 instead of DC.
    Last edited by Audioguru; 14th July 2014 at 02:24.


    1 members found this post helpful.

  3. #3
    Full Member level 6
    Points: 1,509, Level: 8

    Join Date
    May 2014
    Posts
    379
    Helped
    1 / 1
    Points
    1,509
    Level
    8

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    So there wouldn't be any sounds at the output even if light is fallen on the LDR?

    There is a mistake in the circuit? can I replace the speaker with a piezo?



  4. #4
    Advanced Member level 5
    Points: 53,693, Level: 56
    Achievements:
    7 years registered
    Audioguru's Avatar
    Join Date
    Jan 2008
    Location
    Toronto area of Canada
    Posts
    8,747
    Helped
    2051 / 2051
    Points
    53,693
    Level
    56

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    The circuit is almost correct except most speakers will overload the 555.
    I corrected my wrong text.

    If you replace the speaker with a piezo transducer then it might not be able to produce the fairly low frequency from the 555.
    You can replace the 555 circuit with a piece of wire and the LDR and power supply might be able to make a piezo beeper beep when there is light.


    1 members found this post helpful.

  5. #5
    Full Member level 6
    Points: 1,509, Level: 8

    Join Date
    May 2014
    Posts
    379
    Helped
    1 / 1
    Points
    1,509
    Level
    8

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    I've connected the circuit as it is, and made sure using a multimeter.

    the output is: the speaker always have a sound on, either there is light, or there isn't any light, no matter what the value of the pot is set to...always sounds on...

    why and how to solve?



    •   AltAdvertisement

        
       

  6. #6
    Advanced Member level 5
    Points: 53,693, Level: 56
    Achievements:
    7 years registered
    Audioguru's Avatar
    Join Date
    Jan 2008
    Location
    Toronto area of Canada
    Posts
    8,747
    Helped
    2051 / 2051
    Points
    53,693
    Level
    56

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    The 555 is reset and stops oscillating when its Reset pin 4 voltage is as low as 0.3V for some 555 ICs.
    Then you need darkness to produce a very high resistance for the LDR, or a reduced resistance for the 4.7k resistor and-or the pot.



  7. #7
    Full Member level 6
    Points: 1,509, Level: 8

    Join Date
    May 2014
    Posts
    379
    Helped
    1 / 1
    Points
    1,509
    Level
    8

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    This all was tried. Same output. Continuous noise



  8. #8
    Advanced Member level 5
    Points: 53,693, Level: 56
    Achievements:
    7 years registered
    Audioguru's Avatar
    Join Date
    Jan 2008
    Location
    Toronto area of Canada
    Posts
    8,747
    Helped
    2051 / 2051
    Points
    53,693
    Level
    56

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    When pin 4 of a 555 oscillator has its voltage near 0V then the oscillation stops because then the 555 is reset.
    When you connect pin 4 to 0V then does the oscillation stop?

    You said "continuous noise". Is it the buzz sound from the 555 driving the speaker or is it interference maybe even mains hum?



    •   AltAdvertisement

        
       

  9. #9
    Full Member level 6
    Points: 1,509, Level: 8

    Join Date
    May 2014
    Posts
    379
    Helped
    1 / 1
    Points
    1,509
    Level
    8

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    Speaker noise:

    Either the LDR is at full darkness/complete light
    Either the pot is set to max/min/in between



  10. #10
    Advanced Member level 5
    Points: 53,693, Level: 56
    Achievements:
    7 years registered
    Audioguru's Avatar
    Join Date
    Jan 2008
    Location
    Toronto area of Canada
    Posts
    8,747
    Helped
    2051 / 2051
    Points
    53,693
    Level
    56

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    Quote Originally Posted by KhaledOsmani View Post
    Speaker noise:

    Either the LDR is at full darkness/complete light
    Either the pot is set to max/min/in between
    I see the problem.
    The datasheet for a 555 says that the minimum voltage on pin 4 for all of them to stop oscillating is 0.4V.
    The maximum pin 4 current is 0.4mA. Then for the oscillator to stop the LDR must be a very high resistance, the pot must be zero ohms and the 4.7k resistor must be 0.4V/0.4mA= 1k ohms.
    So change the 4.7k resistor to 1k ohms or less.



  11. #11
    Full Member level 6
    Points: 1,509, Level: 8

    Join Date
    May 2014
    Posts
    379
    Helped
    1 / 1
    Points
    1,509
    Level
    8

    Re: What is the difference between a SPEAKER and a PIEZO BUZZER, and how to choose

    thank you man, and greetings to your efforts and logical thinking. good job.

    what is your major of study?



--[[ ]]--