Tone Decoder to Latch - Sensitivity

Discussion in 'The Projects Forum' started by PointyUK, Sep 22, 2013.

  1. PointyUK

    Thread Starter New Member

    Sep 22, 2013
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    0
    Hi All,

    After a bit of googling I managed to cobble together the following circuit...[​IMG] which works as required, I am however trying to make it as versatile as possible and allow plenty of adjustments/tuning.

    I can adjust the mic gain with R5 and the tone required to activate the LM567 with R7. I know I can replace R9 with a pot to adjust the latch output time. What I don't know is how to change to number of pulses/length of pulse needed to activate the latch.

    The tone the mic is picking up can be anything from a single beep which is about 200ms in length to a constant stream of beeps that sounds like a continuous tone. The circuit fires fine on a single beep, so what I would like to do is be able to adjust it so that it only fires on 5 beeps or a continuous tone of about 1 second.

    Finally I had to put much larger values for the Power-on reset for the 555 than the suggested norm (10K/0.1uF) to stop it firing on power up. Any ideas why?

    Thanks in advance for any help you can give a newbie.

    Les
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Did you use any decoupling capacitors at the chips?
    Decoupling or Bypass Capacitors, Why?
    For the NE555 I would use a 10 μF capacitor paralel to a 0.1 μF capacitor,
    as the NE 555 is well known to have a harsh influence on the powerline.
    Without them the circuit will act unpredictable.
    Perhaps that is why you needed to "adjust" your reset circuit.

    Bertus
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,813
    1,105
    You could perhaps have a pulse integrator between the 567 and the 555, so that each pulse from the 567 lowers the Trig input of the 555 step-wise.
    Probably due to the charge time of C3,C4?
     
  4. PointyUK

    Thread Starter New Member

    Sep 22, 2013
    9
    0
    Thanks for the suggestion, I will add that to the design.

    Not sure what you mean Alec, the 567 sends a low pulse, I just don't know how to make the 555 latch require a longer pulse to fire.

    Regards,

    Les
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,813
    1,105
    Try this:-
    Connect the 567 output to one end of a 33k resistor instead of to the 555 trig input.
    Connect the other end of the 33k to V+ via the parallel combination of a 10uF cap and a 680k resistor.
    Connect that 'other end' of the 33k to the 555 trig input.
     
  6. PointyUK

    Thread Starter New Member

    Sep 22, 2013
    9
    0

    Thanks for trying to help, and I am probably being stupid, but I don't understand. We seem to have 3 ends of the 33k resistor!

    Maybe a drawing would help.

    Regards,

    Les
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,813
    1,105
    End 1 goes to 567 out. End 2 goes to parallel combo. End 2 also goes to 555 trig input.
    Can't post one from my PC. Forum software insists on a URL. Grrrr!

    Edit: see if this works
    https://docs.google.com/file/d/0B_ZE8W2iLdNYSUdvRkw3amJHcm8/edit
     
  8. PointyUK

    Thread Starter New Member

    Sep 22, 2013
    9
    0
    Thanks Alec,

    I'll give that a go later, and let you know how I get on.

    Regards,

    Les
     
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