simplest opamp triangle or sine wave ascillator for breadboards

Discussion in 'General Electronics Chat' started by dentaku, Aug 6, 2013.

  1. dentaku

    Thread Starter Member

    Jul 29, 2013
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    What type of oscillator in the audio range (preferably other than square wave) would you recommend a beginner build on a breadboard?
    Something that has a decent chance of working.

    A 555 can make a nice square wave that can be swept through a large range of frequencies very easily and that's fun but I'd like to make something that puts out triangle or maybe even sine waves.

    I have a bunch of opamps laying around and I think I got one to oscillate a while ago but I don't remember which opamp it was. All I know is that it didn't make a very large range of frequencies.

    I've got some LM358N, LM324N, MC1741, TL082CP, LM339N and would like to actually get one to oscillate. Maybe start with the simple square wave then get a triangle later (one that doesn't get quieter at higher frequencies). I just have yet to use an opamp to make something as satisfying as a simple 555 or 556.
     
    Last edited: Aug 21, 2013
  2. joeyd999

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    Jun 6, 2011
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    A single pole RC filter tacked onto the output of the 555 can give you something different than a square wave. Add more poles, and you can eventually get something close to a sine wave.

    An ICL 8038 will do everything you want, including allowing you to do frequency sweeps and change duty cycle for interesting effects.

    Edit: ICL8038 is obsolete and is currently constructed of unobtanium. Sorry!

    Edit 2: You could try the NTE864
     
    Last edited: Aug 6, 2013
  3. LvW

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    Jun 13, 2013
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    What is the idea behind your desire?
    What do you PRIMARILY want? A sinus or a triangle generator?
    There are simple opamp-based solutions for both alternatives which will be able to function without any doubt.
    a) A classical relaxation (first order) circuit for triangle, or
    b) A simple WIEN type oscillator (second order).
     
  4. GopherT

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  5. dentaku

    Thread Starter Member

    Jul 29, 2013
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    I guess I'll start with triangle.
    I got an old B&K oscilloscope and I'd like to test it out with something other than an audio signal or a square wave.

     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    here is a circuit i have used several times, you can use an Lm358, or Tl082, Tlc272, etc


    osc
     
  7. JoeJester

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    You might want to review this document
     
  8. wayneh

    Expert

    Sep 9, 2010
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    The 555 makes a wave resembling a triangle if you look at the voltage on top its timing capacitor, which spends its life either charging or discharging. These are RC exponential curves but look only slightly non-linear because the capacitor is held between 1/3 and 2/3 of Vcc. You can replicate the same thing with a comparator-based oscillator.
     
  9. joeyd999

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    Just be careful not to load the cap. You'll change your frequency.
     
  10. Shagas

    Active Member

    May 13, 2013
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    If you want to try sin waves then you can try a wien-bridge oscillator.
    http://www.learnabout-electronics.org/Oscillators/osc34.php
    That site shows how to make them , starting with simple ones , then going into abit better ones where you can vary the frequency using a dual-ganged potentiometer
     
    dentaku likes this.
  11. dentaku

    Thread Starter Member

    Jul 29, 2013
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    That looks pretty good. I think I'll try that.

     
  12. dentaku

    Thread Starter Member

    Jul 29, 2013
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    I've done that actually (and managed to get a decent triangle-ish wave)and I've noticed that you can easily change the frequency slightly depending on what you have the output connected to.

    Is there a way to fix that?

     
    Last edited: Aug 7, 2013
  13. dentaku

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    Jul 29, 2013
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    Now that's a well organized document with lots of images to help beginners. I like it.

     
  14. wayneh

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    Sep 9, 2010
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    Use an op-amp as a voltage follower. The high impedance input of the op-amp will put very little load on the capacitor and the low output impedance will allow you to drive a variety of loads without affecting the timing. But as long as you have an op-amp, there are basic op-amp circuits to generate triangle waves and you don't need the 555 except for its handiness.
     
  15. LvW

    Active Member

    Jun 13, 2013
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    I am afraid, something went wrong.
    The WIEN circuit is a sinusoidal oscillator - and if your output signal looks not sinusoidal but like a triangle you have build something that works not as desired.
    What is the frequency? I suppose, it will be larger than allowed by the opamps slew rate. Did you use a lamp for stabilizing? You can do that, but there other and better/simpler methods (Diode stabilization or FET control)
     
  16. wayneh

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    I assumed he was referring to using the voltage on the timing capacitor of a 555 timer.
     
  17. Shagas

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    May 13, 2013
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    If you want to learn more about oscillators and stuff , you can try a few of the WIEN sin wave oscillators and then using OP amps to change the sin wave into a square , triangle etc...
    Also try this site :
    http://www.falstad.com/circuit/e-index.html
    Go under the title: Oscillators
    and you will see diffrent types of oscillators in action . It's a real time simulator so you can actually see the "electrons" moving ( you can slow it down and speed it up) which might help you understand how the oscillator works
     
  18. dentaku

    Thread Starter Member

    Jul 29, 2013
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    No, I was referring to the tiangle-ish wave you get from the timing cap of a 555 in that particular post like wayneh and joeyd999 mentioned, not the original op-amp oscillator I originally was talking about.
    It's the first triangle I've ever made on my breadboard that is decent actually but I'm still going to try it with an opamp when I have time to sit down and try it out.

     
    Last edited: Aug 8, 2013
  19. LvW

    Active Member

    Jun 13, 2013
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    OK- in this case, it was a misunderstanding. Sorry for the confusion.
    LvW
     
  20. dentaku

    Thread Starter Member

    Jul 29, 2013
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    OK, so I decided to take an LM339N quad comparator (not strictly an opamp but it does the same job here) and make it oscillate. I just built to Squarewave Oscillator Figure 27 in the TI datasheet and it actually worked.

    I used 110nF instead of 75pF to get lower frequencies and a 100K pot between the output and the inverting input so I can adjust the frequency. It gives my a nice range of frequencies but of course this is just another squarewave.

    SO... I did the same thing that I did with a 555 a long time ago and connected the mic in of my old computer to the timing cap and I got a very triangular shaped wave. It's really not bad at all. I can get from 33.1Hz to roughly 10-11 KHz out of it.
    Here's what it looks and sounds like.
    https://app.box.com/s/axn1bgw611fdetdluft1

    QUESTIONS?
    Why is it that I can plug this straight into the mic in of the cheap onboard sound of my old computer (well, it goes through a 10uF cap first) and it works fine BUT if I plug a little 4ohm speaker to this circuit I get nothing from the triangle wave made by the cap?
    It works fine when I plug the speaker into the squarewave output (pin 2) of the LM339N.

    ALSO, I'm assuming there's some sort of low pass filter happening here ??? because it gets quieter when I go up into the high frequencies.
    It starts to get obviously quieter around 6KHz. I can fix it in software by brickwall compressing it but that's just a roundabout fix that won't teach me anything about the hardware side of things.
     
    Last edited: Aug 11, 2013
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