Integrator circuit questions...

Discussion in 'The Projects Forum' started by envytea, Jul 7, 2008.

  1. envytea

    Thread Starter Member

    Feb 18, 2008
    10
    0
    Hellos to all,

    A couple of weeks ago, I posted here having problems getting an integrator circuit working. Upon, taking some advise and trying a few things, the problem remains. I have a TL082 op-amp from which I am trying to generate square wave and triangle wave. I have built this up on the breadboard, but I am only getting the square wave. The 100K variable resistor changes the frequency to cover my desired range of the square wave, but the second half of the circuit (the triangle wave) does not work correctly. When I tap in at pin 1 (the triangle output) with headphones, there is a weak noise that does not change with the 100K variable resistor being manipulated. Then, when I remove the 7.16K resistor, there is a seemingly triangle wave at pin 1 that has a very high frequency, is relatively faint, and changes frequency in response to the variable resistor manipulation. I want to be able to tap into the circuit at pin 1 or pin 7 for the two wave forms. I would like each wave to have similar amplitudes, and have the frequency of each vary with manipulation of a variable resistor. The schematic is as posted here:


    Oh, thanks for the circuit templates Bill. I am making some progress in diagramming.

    Nick
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Your headphones are a very heavy load; between 4 and 32 Ohms. It's nearly like putting a dead short on the output of the opamp. This is causing the circuit to cease oscillation the moment you connect it up.

    You need to use a voltage follower or audio amplifier IC, like an LM386.

    You will need to use a resistive divider between the input of the audio amp and the oscillator, or you will blow your eardrums out. Be careful to keep the sound setting low, you only get one set of ears per lifetime.

    See the attached for an example how you might connect in an LM386 audio amp.
     
    Last edited: Jul 7, 2008
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    An opamp doesn't have enough output current to drive most headphones. The minimum load for most opamps is 2k ohms. A few opamps can drive 600 ohms. Your headphones might be 32 ohms which is like a dead short to the output of an opamp.

    Use a power amp to drive headphones (be careful it is not too loud) and use your generator to drive the input of the power amp.
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Check this thread out.

    If you're using headphones you might add something like a 470Ω resistor between the headphones and the switch, it will be weak but should be audible.
     
Loading...