help building a variable sine wave generator

Discussion in 'The Projects Forum' started by pkennedy, Feb 27, 2009.

  1. pkennedy

    Thread Starter Active Member

    Feb 27, 2009
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    hey everyone I am new to the forum and would like any information on building a function genarator. I would like to have a schematic to follow because I am fairly new to electronics to.any help would be appreciated.
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Do you want also other waveforms besides the sinewave ?

    Greetings,
    Bertus
     
  3. pkennedy

    Thread Starter Active Member

    Feb 27, 2009
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    well for now just the sine wave I dont want to complicate things to much also with a low output voltage
     
  4. bertus

    Administrator

    Apr 5, 2008
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  5. thingmaker3

    Retired Moderator

    May 16, 2005
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  6. davebee

    Well-Known Member

    Oct 22, 2008
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    An alternative to building a variable oscillator from discrete parts would be to use an integrated circuit designed to implement a complete function generator.

    The MAX038 is a good example, but it seems to be discontinued. But there are others, as suggested by this thread:

    http://forum.allaboutcircuits.com/showthread.php?t=1349
     
  7. onlyvinod56

    Active Member

    Oct 14, 2008
    362
    1
    Hi
    i have xr2206. I want three sine waves, each have a phase shift of 120 deg.
    Is there any simple technique to get this?
    from this forum i came to know that using RC components we can achieve this.
    I have simulated this in PSIM. but the voltages of three phases are going different.

    check the attachment. i need to construct that. can anybody help me to get the three ac voltages?
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello onlyvinod56,

    What you are doing now is hyjacking.
    The answer can be found in the PDF thingmaker3 pointed pkennedy to.

    Greetings,
    Bertus
     
  9. onlyvinod56

    Active Member

    Oct 14, 2008
    362
    1
    hello bertus,
    I have seen the thingmaker link. But all those oscillators are manually controllable. I need to control the frequency of the oscillator by giving a controlled volatge to a certain pin.

    http://www.educypedia.be/electronics/spwmsimulation.htm

    I dont know any method to control the frequency with a voltage for the collpits, hartley, RC phase shift oscillators etc.,
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Here is the adapted circuit from the PDF pointed by thingmaker3.

    [​IMG]

    To make the frequency variable you can place a analog switch (like a 4066) with a lower resistor parallel to the frequency determing resistors.
    By pulsing the 4066 with a high frequency PWM (about 100-1000 times the wanted frequency) the effective resistance will change with the pulswidth.

    Greetings,
    Bertus
     
  11. pkennedy

    Thread Starter Active Member

    Feb 27, 2009
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    Hey thanks for all the help I will check some of these out
     
  12. pkennedy

    Thread Starter Active Member

    Feb 27, 2009
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    please forgive my ignorance but i didn't find a variable frequency sine wave generator
    except for the three phase one and I should have said before but I need one that will vary from about around 5 to 10 Hz to maybe 1Khz I will be using it to run leds and small buzzers.It will be mainly for school projects and will never be for any big load
    I know I could buy one but I would really like to build one myself.And ic circuit would be fine if I could have a way to very the frequency and what would the source signal have to be?
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    If you want to experiment here is a design I haven't tried yet, but will eventually. One of my long term projects is to come up with a simple function generator similar to what you describe, but I'm currently working on the long durration flashing LED articles.

    [​IMG]

    Use blue or white LEDs, I'm using them for the voltage drop, or zener diodes. R1 and R2 can be 1KΩ, and the 5KΩ is adjusted for the best sine wave approximation.
     
  14. pkennedy

    Thread Starter Active Member

    Feb 27, 2009
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    thanks I am going to start building this right now and sorry about my previous statement I didn,t scroll down far enough on one of the links given on the thread.sorry bertus
     
  15. pkennedy

    Thread Starter Active Member

    Feb 27, 2009
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    I built the circuit but i dont see oscillation on the scope.what value do i need for the cap after the taransistors?I see the formula but don,t really no what baseline to start from my value may be way off and that may be the problem.bothe leds light up though
     
  16. pkennedy

    Thread Starter Active Member

    Feb 27, 2009
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    i am using a 6 volt source to Vcc.the board i am using has a built in power supply from dry cell batteries it has differant supply voltages to choose from if that helps
     
  17. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Can you post a schematic you used ?
    (there are many around).

    Greetings,
    Bertus
     
  18. pkennedy

    Thread Starter Active Member

    Feb 27, 2009
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    okay I am getting a sine wave and a square wave but the triangle wave (node b)is also a sine wave?but I still got what I asked for plus a little more so I appreciate the help
     
  19. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What frequency are you using ?
    What type of opamp are you using ?
    If the bandwith of the opamp is not large enough the output B can be distorted.

    Greetings,
    Bertus
     
  20. pkennedy

    Thread Starter Active Member

    Feb 27, 2009
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    I used the schematic on this thread posted by bill.a 272 op-amp
    I want a low frequency from about 10 hz to 1khz
     
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