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Help with siren circuit

Discussion in 'General Electronics Discussion' started by dislocations, Jul 20, 2013.

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  1. dislocations

    dislocations

    25
    0
    Feb 21, 2012
    Hi,
    Hope u are all well since my last visit here (2 years ago?).
    I'm looking for a bit of help with a circuit I'm building. It's a siren based on a 555 which is familiar to many of you. I'd like to make the rise and fall quite long, around 10 seconds from low to high and back to low. I would like to make this a sine wave.
    I also thought of using a 40106 instead of a 555 as I prefer the ease of use. If I did it that way I would use 2 40106's......one modulating the second.
    In the past I've sort of acheived this kind of thing by putting a large cap from the output of the first to ground. I realise this is not the best way? I'd also like to be able to alter the frequency of the first.
    Thats probably as clear as mud? Sorry!!! :eek:
     
  2. dislocations

    dislocations

    25
    0
    Feb 21, 2012
    Anyone, please!
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    You could start by posting a schematic of your ideas so far.

    You would like to make "this" a sinewave? The audio signal, or the modulation signal?

    You can use a 40106 as a modulated oscillator, but the thresholds are not well-controlled, compared to a 555 where the thresholds are pretty close to 1/3 VCC and 2/3 VCC.

    If you want a slow sinewave for your modulation frequency, you might be best to use a two-op-amp triangle/squarewave oscillator followed by a sine shaper. Alternatively you could use direct digital synthesis, but if you go digital it would be simpler to do the modulation inside a microcontroller, using a sinewave lookup table.
     
  4. dislocations

    dislocations

    25
    0
    Feb 21, 2012
    Thanks! I thought op-amp would be the way to go
     
  5. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Old electronic organs used a phase shift oscillator to generate low frequencies for vibrato. These ran at about 1Hz. Larger capacitors would give lower frequencies I could look up the circuit if you wish.
     
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