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555 timer audio switcher question

Discussion in 'Electronic Basics' started by milo, Feb 15, 2004.

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  1. milo

    milo Guest

    hi everybody

    i am trying to build a circuit that will switch an audio signal on and
    off, using a 555 oscillator. Basically i want the audio signal to be
    fully on when the oscillator waveform is hi, and fully off when the
    waveform is low.
    What is the best way to do this?
    i have tried connecting a transistor to the output of the circuit, so
    that the base termainal is connected to the pin3 output, and collector
    and emmiter are connected to the audio signal path. i used a 2n3055
    transistor. It worked quite well, but the problem was, even when
    waveform is low, a small part of the audio signal slipped though and
    could be heard. I want it to be fully off, then fully on. How can i do
    this? what transistors are most appropriate? should i use two
    transistors, with one switching on the other?

    Thank you
  2. Forget the transistors, make it easy for yourself and use a 4066
    analogue-switch. One IC does all the switching you require, will work
    straight from the 555 oscillator.
  3. John Fields

    John Fields Guest

    Are you trying to switch an audio signal going to speakers, or to the
    input of an amp, or??? That is, what voltages and currents are we
    talking about?

    Is the audio signal real AC, like something that goes above and below
    zero volts, or something else?

    Inqiring minds want to know!-)
  4. Si Ballenger

    Si Ballenger Guest

    I use a simple tranisitor to switch the audio along with the
    video on my webcam page below. It is a line level signal. To
    prevent bleed over on full off, you may need to connect the audio
    feed to a ground when it is in the off position.
  5. Jamie

    Jamie Guest

    if you can find some 4066 or equ bilateral mos gate switch
    you can turn off the audio very nicely..
    P.s. you will have to do this at the preamp stages because
    this unit is very low current drain compared to what your
    currently using :))
  6. milo

    milo Guest

    thanks for replying

    ideally i want my audio switcher to switch either AC line level or AC
    to amplifier level. Would this cmos chip be good for this?
  7. Your spec is still rather vague. What does 'either AC line level or AC
    to amplifier level' mean? Do you mean you want to switch either:
    - a low voltage, low current AC input signal
    - a high voltage, highish current amplifier output signal.

    If so, then the former would be easier, so why not forget about the
    latter? Switching the low-level signal probably *could * be handled
    with a CMOS 4066 chip.
  8. w_tom

    w_tom Guest

    Without putting numbers to 'high', 'low', 'AC line level',
    and so many other expressions; then many are simply ignoring
    your post. Any response would be futile. If you want a junk
    science answer, then use a high pass or low pass filter. Is
    this reasonable? Only if the answer does not include numbers.
  9. milo

    milo Guest

    bloody 'ell... all these numbers..... . . . ..

    ok, i think i know how to put it know. i want to use a switch,
    triggered by the 555 output pulse, that is capable of switching large

    by 'large' i mean waveforms that are up to 10v p-p amplitude. this
    would be the absolute maximum though, i think that most wavforms i
    would use would be under 5v p-p. maximum current probably about 10 mA
    ..i spose that a cmos wouldn't be able to handle this.
  10. More numbers: the 4016 and 4066 can dissipate up to 100 mW. So,
    assuming your 10 Vpp is roughly 3 V rms, that means the current
    through the switch could be up to 30 mA absolute max. Therefore 10 mA
    should be OK. But voltages *must* remain within the CMOS chip's supply

    I suggest you now track down and read the datasheet.
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