Current Activated Buzzer Circuit Advise

Discussion in 'The Projects Forum' started by rocksolidsr, Apr 15, 2009.

  1. rocksolidsr

    Thread Starter New Member

    Apr 15, 2009
    5
    0
    I'm trying to have a buzzer beep when current is applied to a transformer, spec sheet attached. I have an idea of what I would do I just want to run it by you guys and see what you think

    I was thinking of using one of these current sensors and run the output wire through it and use the output of that to run this circuit to make the buzzer beep.

    Do you think this would work, the output of the transducer is high voltage, high frequency >20khz

    is there a better way?

    thanks
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Success will depend on your switch. How much current do you expect to measure with your current transducer? (What will be the expected current transducer output voltage?)
     
  3. rocksolidsr

    Thread Starter New Member

    Apr 15, 2009
    5
    0
    Ok I measured the output of the transducer using this current probe
    here is what i got with the probe set to 100mA/V
    Cyc RMS = 472mV
    Rise Time = 14.84us
    Fall Time = 18.20us
    Pos Width = 24.7us
    Neg Width = 24.20us
    Freq = 20.45kHz
    Period = 48.90us
    Mean = 68.7mV
    Pk-Pk = 1.54V

    so from those measurements I am seeing that I would probably need to measure current up to 154mA?

    and the output of the transducer is 2.5 V, I was thinking of using a relay for the switch
     
  4. rocksolidsr

    Thread Starter New Member

    Apr 15, 2009
    5
    0
    i'm kinda stumped here, i'm trying not to mess with the original circuit if at all possible, what is the easiest way to detect output from the transformer and have that output a voltage signal of at least 2.5V

    I have the buzzer circuit working with a 555 timer and a npn transistor but i'm not sure how to only activate it when there is output from the transformer

    any help would be greatly appreciated thanks.
     
  5. rocksolidsr

    Thread Starter New Member

    Apr 15, 2009
    5
    0
    So I took my small signal and ran it through a LM741 op amp, using a +-12V supply and it worked, schematic below.

    [​IMG]

    However that was just a test to see if it would work, now I need to figure out how to power the op amp with just a single supply of either 5V, 14V, or 24V. I tried using the 24V supply and using a voltage divider to create a virtual ground but when I do that I get -21V, and like 2.5V which is strange, schematic below

    [​IMG]
    any ideas?
     
  6. rocksolidsr

    Thread Starter New Member

    Apr 15, 2009
    5
    0
    So I think I know why I'm not getting a very good output from my op amp and that is because the signal I'm getting is being pulsed so it isn't ON the whole time, it is ON 32ms and OFF 32ms is there a way to get a constant signal from that somehow??
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    When you increase the value of C2 (to say 22 uF, experimental value) the pulses will be accumulated in the capacitor.
    The capacitor will create a buffer for the off times.

    Greetings,
    Bertus
     
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