Please help me with this circuit

Discussion in 'Homework Help' started by A212, Apr 20, 2008.

  1. A212

    Thread Starter New Member

    Apr 18, 2008
    7
    0
    Please help I have no Idea how to do this.

    -I need some help to designing circuit that accept 5Vpp input sinusoid of variable frequency. The input signal is assumed to originate from source with 50 Ohm impedance .

    - The circuit to indicate when the input signal id < =5 KHz by turning off an LED when the input frequency Exceeds the specify value. In another words, The LED is to be on when frequency <= 5Khz ( +25%) or (-25%).

    - Circuit to consist of only Resisters, Capacitor and LED.

    Thanks a lot
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    place an led and a resistor in series, then a capacitor in parallel with them (both) and finally a resistor in series with the whole circuit you made before. if you dont know how to calculate the values use a circuit simulator to find the approximate values.
     
  3. A212

    Thread Starter New Member

    Apr 18, 2008
    7
    0
    Hi thanks alot for your help.

    Could you please tell me if there is any way to calculate the values without circuit simulator.

    Also, could name some circuit simulator.

    My problem I'm new in this major.

    Thanks alot again for help.

    A212
     
  4. guitarguy12387

    Active Member

    Apr 10, 2008
    359
    12
    Pspice is a common one.

    Yup. You should be able to use what you know + nodal analysis to find some stuff. Thats the short answer without going through and actually grinding the numbers.
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Read the AC section of this website about capacitors to see how you calculate the reactance of a capacitor. Then assume the resistor capacitor combination as a voltage divider to find at what value of capacitance it will output enough voltage to turn on the led. Of course this is not very accurate because of the current will be drawn by the led but is going to work. You can search for low pass filters in google if you like.

    Try Multisim for a simulator. You can download it with a torrent file. you know cracks ........;)
     
  6. A212

    Thread Starter New Member

    Apr 18, 2008
    7
    0
    Hi
    mik3 , guitarguy12387

    Thank you so much for your help;


    A212
     
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