signal turn on led

Discussion in 'General Electronics Chat' started by guyromb, May 15, 2009.

  1. guyromb

    Thread Starter Member

    May 5, 2009
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    hello,

    I have a reciever that on his output i get 1khz sound (i can hear it using headphones) - I would like to turn on a simple led when this sound is heard. I also built a highpass\lowpass active filter.. I thought to use xor gate but not sure.

    Please help me:)

    thanks
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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  3. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You have made a filter that works.
    Afther this filter you can place a audio level meter.
    http://www.mitedu.freeserve.co.uk/Circuits/Audio/palm.htm
    On the place of the meter you can place a comparator.
    The comparator output will let the led trun on when the level is over the adjusted threshold.

    Greetings,
    Bertus
     
  4. guyromb

    Thread Starter Member

    May 5, 2009
    28
    0
    thanks.

    I prefer bert's circuit (i have the components). The highpass\lowpass filter seems to work.. but the volume is low - should i amp. it again? (which resistors to use?) - i use lm324 (quad op.amp). This is the l\hpass circuit:
    [​IMG]
     
  5. guyromb

    Thread Starter Member

    May 5, 2009
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    Can the comparator be op.amp too ? but i am not sure about the voltages comparison (i get low voltage on the filter output)
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Are you using a single powersupply voltage?
    Then you can not connect the + input of the opamp to ground.
    You can make a "virtual" ground by using two equal resistors (say 10K) with a capacitor of 10 uF from the midpoint to ground.
    The top of the capacitor is your "virtual" ground.
    This you can connect to the + input of the opamp.

    Greetings,
    Bertus
     
  7. guyromb

    Thread Starter Member

    May 5, 2009
    28
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    Thanks!! so just tell me if i understood correct:
    op.amp+ leg -> 10k resistor -> 10k resistor -> 10nf Capacitor -> ground.
     
  8. guyromb

    Thread Starter Member

    May 5, 2009
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    leg 11 ( op.amp gnd) and leg 4 (op.amp vcc) can be conntected as normal to the +\- right?
     
  9. guyromb

    Thread Starter Member

    May 5, 2009
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    Now i hear the sound clear and strong !!!!!!!!!!!!!! :D
     
  10. guyromb

    Thread Starter Member

    May 5, 2009
    28
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    Can you explain me about the "virtual ground" please?
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have drawn in your schematic what I mean.

    [​IMG]

    Greetings,
    Bertus
     
  12. guyromb

    Thread Starter Member

    May 5, 2009
    28
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    bert .. i tried your circuit but i hear the 1khz very low again... Moreover, when I transmit the sound or not - i get the almost same output voltage.
    However, by chance i got the sound very high (also i see on the voltmeter that there is a change in the output voltage).

    What i did:
    leg 3 (op.amp +) to 10kohm to 10kohm to 10microfarad to ground.... but not sure if it's good :D
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    Pin3 should be at half the supply voltage. Maybe your input source is grounding the voltage at pin3.
    Make the circuit like this and look in Google for Multiple-feedback Bandpass filter.
     
  14. guyromb

    Thread Starter Member

    May 5, 2009
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    Is that bandpass filter circuit for 1khz pass? I forgot to mention that use ~5-6v power
     
  15. guyromb

    Thread Starter Member

    May 5, 2009
    28
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    It's just killing me that i have done everything and it works.. and just the simple thing - turning on a led - doesnt work :(
     
  16. guyromb

    Thread Starter Member

    May 5, 2009
    28
    0
    Please, somebody can help me?
    I can hear the 1khz using headphones on the reciever output... I just need to convert this sound signal to '1' logic only when this it's heard.... I tried many things and I really don't know what to do :(:(
     
  17. guyromb

    Thread Starter Member

    May 5, 2009
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    Last edited: May 16, 2009
  18. Audioguru

    New Member

    Dec 20, 2007
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    The filter should feed a level-detector circuit. It turns on the LED.
     
  19. guyromb

    Thread Starter Member

    May 5, 2009
    28
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    I would expected that i would see a voltage differents - when i transmit or not
     
  20. guyromb

    Thread Starter Member

    May 5, 2009
    28
    0
    so what do you recommend me to do?
     
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