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555 metronome with leds

Discussion in 'LEDs and Optoelectronics' started by Vitautas, Mar 23, 2012.

  1. Vitautas

    Vitautas

    6
    0
    Mar 19, 2012
    Few days ago I asked about equalizer circuit, but now I understand that it is a bit too complicated for me. So I searched for something easier to build and found this metronome circuit:
    [​IMG]

    What I would like to know is how can I add 4 leds that will flash alternately at every beat.
    Also, why is there a transistor and what kind of speaker or piezo element should I use so that the measurements of the metronome would be as small as possible?

    I think the audio amplifier isn't necessary?

    And one more thing. The bigger the Vcc, the louder the volume?

    Thank you.
     
  2. twister

    twister

    161
    6
    Feb 12, 2012
    The amp is necessary with an 8 ohm speaker. 5/8=0.625A
    It is not necessary with a 32 ohm speaker. 5/32=0.156A
    Look up the data for your 555 to see how many amps it puts out.
    You could hook a 500 ohm to pin 3 and to a led to ground.
    You could hook a 500 ohm to VCC and to a led and to pin 3.
    They will flash alternately.:)
     
  3. Vitautas

    Vitautas

    6
    0
    Mar 19, 2012
    But what about 4 leds?
    And do I really need an amp when using 8 ohm speaker? That's a disappointment:(
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    9,404
    1,921
    Nov 17, 2011
    An 8 Ohm speaker needs too much power. The 555 isn't up to this task. Adding a single transistor should not disappoint you.

    4 LEDs in series need at least 4*1.6V=6.2V if you use red LEDs. Using other colors will require even more voltage. So with 6V the thing you can do is take 2 LEDs in series and add a suitable current limiting resistor in series (see the tutorial on LEDs in this forum).
    Put two of these series packs in parallel and you have 4 LEDs. Add another transistor similar to the one for the speaker, but leave out the speaker. Put the LED pack into the collector wiring and add a base resistor with a value of approx. R=5V/(100*I_LED) into the base wire. See this schematic block diagram:
    [​IMG]

    Harald
     

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  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,214
    2,695
    Jan 21, 2010
    You're essentially driving the speaker with DC. It's really bad for it.

    You would be better off doing something else. I'd recommend (perhaps) a short burst of signal (say 1kHz) at each beat. You could than capacitively couple the speaker to the 555's (this would be a second one) output. It would be enabled by the short pulse generated by the first 555 (the one you show). Also you would probably want to reduce the duty cycle somewhat.

    An AC signal to the speaker is going to sound WAY louder too.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    9,404
    1,921
    Nov 17, 2011
    For a metronome a capacitor in series with the base resistor may be suitable. After all, you only need a "click" sound.

    Harald
     
  7. Vitautas

    Vitautas

    6
    0
    Mar 19, 2012
    [​IMG]
    [​IMG]
    I drew the schematics to run transient analysis. I calculated that when R1 is 70k, the output frequency should be 2Hz. And it is, but why is the signal inverted?
    Two diods in series should simulate red led. Is 1k before the leds enough?
    Should I use electrolytic capacitors?
     
  8. duke37

    duke37

    5,256
    726
    Jan 9, 2011
    A 555 gives an asymetrical output in that circuit.
    I am no expert on the 555 but I think that a symmetrical output can be obtained by disconnecting pin 7 (discharge) and connecting R1 to output instead of Vcc.
     
  9. Vitautas

    Vitautas

    6
    0
    Mar 19, 2012
    Now I found this.
    [​IMG]

    But where should i connect pin 5, because pspice gives error.
     
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