xr2206 function generator

Discussion in 'The Projects Forum' started by poindexter, May 12, 2007.

  1. poindexter

    Thread Starter Member

    Aug 26, 2006
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    0
    Hi,Im making a sine wave generator from a xr2206.Ive made it and Im happy with the wave and I can adjust to different frequencies.What Im not happy with is I can only get amplitude of about 2volts.I tried to hook it up to a 741 op amp but am not having much joy.Id like to get the wave to say 10volts if possible.Does anyone know how to do this or where Im going wrong.Thanks
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The 741 is an older generation op-amp and as such its output driver structure has some shortcomings when its output is called upon to swing close to the positive or negative rail. What you need is what is referred to as a "rail-to-rail" op-amp for your application. You did not mention what the upper limit of your frequency range target happens to be. You will need to take that into consideration when chosing a candidate op-amp.

    hgmjr
     
  3. poindexter

    Thread Starter Member

    Aug 26, 2006
    10
    0
    ok.I know what you mean about the frequency,at present probably 50khz would be enough.You see Im a student and want to do my pracs at home.When I had a small gain inverting op amp I still got an output but it was limited to about 4 volts.It seems that the output from the function generator would be reduced from about 2 volts to about 2-300mV.At higher gains I simply got no output from the op amp.Does this sound right to you?
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    If you post a schematic of your circuit maybe we can figure out what is going on.

    hgmjr
     
  5. poindexter

    Thread Starter Member

    Aug 26, 2006
    10
    0
    here is a drawing of the inverting op amp.If I use values R2=10k and R1=1k then I cant get an output.If I use R2=1k and R1=500 then I can get an output but at that time the output from the function generator is reduced.

    741.jpg
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The value of resistor R1 in your op-amp is the load resistance presented to the output of the xr2206. Naturally, the greater the value of R1 the less the output of the xr2206 will be loaded.

    With +/-15 volts as your power supply to the 741 you should be able to get a +/-10 volt output swing without needing to resort to a rail-to-rail op-amp.

    Also, with R1 = 500 and R2 = 1000, that will only be a gain of 2 which may not be enough to get your amplitude up to the level you want.

    Have you considered reconfiguring your 741 to be a non-inverting opamp? That will help increase the input impedance.

    hgmjr
     
  7. poindexter

    Thread Starter Member

    Aug 26, 2006
    10
    0
    Hey thanks for your help.I went back to some old notes and they had a circuit there which is hooked up to the supply differently.I set it up and now I have it working perfectly.Now that I look at it more closely I see this is a non inverting op amp setup.So I guess you were right.Last month I built my first project,an electronic dice and I was really proud.Now Ive made my own function generator I m so stoked.Thanks brother.Do you think anyone would like to see these circuits?Should I post them? see ya later thanks again
     
  8. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    By all means, please post pictures of your handy work. Congratulation on your success. It sounds like you have been bitten by the bug.

    hgmjr
     
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