adding a speaker to LED throbber

Discussion in 'General Electronics Chat' started by McGuffin, Oct 15, 2009.

  1. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    was looking in another thread and was wandering how hard would it be to add a speaker to a Pulsing LED set up? Would you get a beep or would you get a frequency sweep going from on tone to another as the voltage makes the LED pulse? also what kind of speaker would be ideal like a Head phone speaker or something from a cell phone?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    This could be done, not sure where you want to go with it. Make a simple hysteresis oscillator, then connect the pulsing signal to pin 5 and take a listen.
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    If a pulsing LED circuit is modified to produce enough current to drive a speaker then the speaker will go POP when the LED lights then it will go POP again when the LED turns off.
    A POP does not sound like a beep and it is not a tone. You need an oscillator circuit to make a beep or a tone. Then you need a logic gate to turn the oscillator on and off.
     
  4. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    so add the oscillator with what type of gate. Ie And or nor exor what input would be needed from the 555 would it come from the 5 pin to the gate or another design.
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    If you use a 555 oscillator then its RESET pin #4 turns it on and off.

    A 555 produces a square-wave that sounds like a buzzer. The 555 does not have enough output current to ddirectly drive a speaker.
    A sine-wave sounds like a tone.
     
  6. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    ok so how would you set up a pulsing led circuit to Have a speaker emit a low hum along with the led? so you would see the led pulse but it would give off a sound as well.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    You forgot to post your LED Pulsing circuit.
    A speaker needs to have an enclosure designed for its spec's to emit a low hum.
     
  8. Wendy

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    Mar 24, 2008
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    AG, this is a continuation of a previous thread, which you posted in.

    Here was the last schematic shown.

    [​IMG]

    I mentioned it, but go to the 555 Hysteretic Oscillator article, use a capacitor and a 150Ω resistor on the output to connect a speaker to pin 3, and conned Pin 6 of this circuit to pin 5 of the other 555 oscillator. Adjust the tone to match what you want.
     
  9. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    could you use a 556 and achieve the same thing by building the oscillator on on side and the above schematic on the other?
     
  10. Wendy

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    Mar 24, 2008
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    I've been putting some thought into it, you probably want a lower freq when it is dim, higher when it is brightest. The 555 will have to have this signal inverted.
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    OK, here is how I would do it. I really didn't like the transistor version, so I added a version using an op amp. Basically I'm thinking a low voltage unit similar to a LM324 or what not.

    [​IMG]
     
  12. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    cool ill try both methods and see which one works best.
     
  13. Wendy

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    The speaker is likely to be pretty low volumn, which may be what you want. If you need louder let me know, there are ways of boosting a 555 output.
     
  14. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    yeah i would like it that you can hear it from 10-15 feet away with slight background noise
     
  15. Wendy

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    Mar 24, 2008
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    OK, here are some ideas I doodled a while back, they haven't been built, but I believe they will work OK.

    [​IMG]
     
  16. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    these last are for the 555 on the end with the speaker to boost out Put?
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    Yep. Missed ya, wondered if you had given up on us.
     
  18. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    no had soe other projects that needed my attention. Im building the one from the top with the op amp now and ill in corporate the booster fort eh speaker as well. Im using a cmos 555 for the speaker side will it still be ok to use the same resistors and caps or would it be better to change them to different values?
     
  19. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    ok i built the one on the top of this page. Should the Vcc and ground be connected on a 741 8pin op amp? or just connected like is shown?
     
  20. McGuffin

    Thread Starter Member

    Sep 19, 2009
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    ok Its all set up like at the top but all I can hear is a small pop when I put my ear to the speaker other than that there is no audible tone. the LED pulses fine.
     
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