XR2206 faulty I.C?

Discussion in 'The Projects Forum' started by Neil Groves, Sep 28, 2013.

  1. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    Hi guys

    I am building a function generator based around the above I.C, I have got a wonderfully clean square wave but when I vary the voltage on pin 3 to adjust the amplitude, nothing happens.

    just for test purposes I have a pot one end on 12V, one end on 0V and the wiper going direct to pin 3 of the device, the voltage on pin 3 varies as I would expect on pin 3, but the output of my square wave stays constant, I am wondering if I might have a faulty chip?

    Neil.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,420
    3,355
    It might help if you provided us with the complete circuit diagram.
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    You are not supposed to connect a potmeter between 0 and +12 Volts on pin 3.

    [​IMG]

    The pin 3 is for adjusting the output voltage of the sinewave and triangle.
    It will do nothing on the squarewave.

    [​IMG]

    Bertus
     
  4. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    I am just configuring it that way for test purposes Bertus.

    ok I will experiment with the other waveforms and see what happens.

    thanks

    Neil.
     
  5. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    ok just checked things out and yes the sinewave output (pin2) responds nicely to voltage applied at pin 3, BUT.....the peak to peak of the sinewave itself doesn't adjust, only the D.C level on which it sits varies?

    Neil.
     
  6. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    So how can I get the bottom of the sinewave to sit at 0V? if I add a cap in series with the output the sinewave straddles the 0V rail. being equally above and below......or is this how it is supposed to be?
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,420
    3,355
    If you put a cap in series that is called a DC blocking capacitor, i.e. it blocks the DC.

    In other words it makes the average voltage zero.

    That is what a DC blocking capacitor is supposed to do. It would make a perfect sine wave straddle 0V.
     
  8. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    Great, it's all working then, thanks everyone for your help.

    Neil.
     
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