Guide me for successfully making a single LED react to sound frequency

Discussion in 'The Projects Forum' started by vadimqew, Apr 16, 2011.

  1. vadimqew

    Thread Starter New Member

    Apr 9, 2011
    Hello there again,

    This is my second thread so far for the same project. I have tried to make a very simple color organ. I have tried to make more complicated with 3 LED but no success. I need some guidance from you.

    What I'm trying to do is have an LED react to a certain input frequency from a sound source like 3.5mm jack. I'm doing this for a school project and the more I research, the more complicating it gets for me. The time is running out for me so I'm forced to do just a simple one.

    I would preferably make the circuit out of the parts I have already.

    op-amp LM358N (can be powered by a single source as low as 3V)
    Transistor - NPN TIP120 (too powerful? 65w)
    can get any close value resistors and some LED
    2 9Volt batteries
    3.5 mm jack
    and only .1 micro Farad Capacitors

    So far i have tried following this circuit

    the guy that made the circuit said to use the formula below to find the unknown values.
    I have used his formula (frequency=1/(2*pi*R*C), and I'm assuming the just for that filter R3=R4=R8=R11 so My R was 13.26K at 120Hz with the use of .1 microFarad capacitor

    Here is the circuit I want to build, but not all the values are known to me and if it should work. It is a inverting single power supply connection. I was wondering if the right Rf and Ri values are found, could it be used as a filter to filter around 2Khz as an example for mids. Circuit is shown below. I would appreciate any help and if anyone could guide me into finding the right values for either the first full circuit or the one i drew myself. Someone before suggested looking at their chapter 12 they wrote, but the circuits are too complicated for me to understand, I'm just getting into this so the basic, the better.

    thank you
    have a wonderful day
  2. vadimqew

    Thread Starter New Member

    Apr 9, 2011
    someone please help me
  3. beenthere

    Retired Moderator

    Apr 20, 2004
  4. qlue

    New Member

    Apr 15, 2011
    I don't want to discourage you, but you're trying to run before you can crawl. :(
    The second circuit, the one you drew yourself, doesn't make much sense to me.
    However, in the first circuit, R7 to R9 will be the same value, probably 470K should work. Resistors R1 to R6 will all be the same value and will depend on how much gain you need. (try 47k, that will give you 10x gain which should be good enough for a standard audio socket as source)
    Now about frequency.
    I'm not sure what you mean about a 2000Hz range?
    The formula you've been given is for calculating a cut-off frequency.
    The first part of that circuit, at the top of the diagram, is a low pass filter. It will block frequencies above the frequency.
    The middle part of that diagram is a high pass filter. It will block any frequency lower than the cut off frequency.
    And the last part at the bottom of the diagram is a band pass filter. I will allow a small range of frequencies that peak at the cut off frequency.
    Remember that in your formula, R is in ohms and C is in farads.
    I hope this helps you.