Unable to get a Wien bridge oscillator to work

  • #1
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Main Question or Discussion Point

I am unable to get the wien bridge
Oscillator I built to work. This same
Circuit has worked several times. Sometimes the same circuit works.
Sometimes the same circuit does not work. When it works I can get
A led to blink and can build a frequency divider. How do I troubleshoot this circuit?
244770


This a drawing of the circuit I am using.
 

Answers and Replies

  • #3
LvW
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Did you create the circuit by yourself? I never have seen such a circuit.
Didn`t you consult any textbook or any of the hundreds internet contributions?
 
  • #4
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I consult an article on the internet. It
Show me a schematic and I used that.
 
  • #5
257
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I have been unable to get the circuit
Svein showed me to work.
 
  • #6
Baluncore
Science Advisor
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Before we can help you we need more information.

You need to check your circuit carefully and redraw your schematic diagram.
You must show all component values you used.
What type of op-amp do you use?

You show R2 in the wrong place for a wien bridge oscillator.
Replace the resistor that goes to the (+) input with a wire.

The ratio of R10 to R11 divider sets the gain which is essential for oscillation.
Some non-linear amplitude regulator is needed in that divider to reduce distortion.

You do not show ground clearly.
Also, what power supplies are used for the op-amp relative to ground.

The battery and LED shown as the load has no limit resistor.
That load might overload the op-amp and prevent oscillation.
What voltage is that battery?

244922
 
  • #7
LvW
812
217
I consult an article on the internet. It
Show me a schematic and I used that.
Either the article was wrong - or (most probably) you made an error during redrawing the circuit on your paper.
Carefully, check the circuit and use additional resources. There are hundreds of papers dealing with this basic circuit.
 
  • #8
257
3
After I started this post I managed to
Get the circuit I drew to cause a diode
To blink. I can get the diode to blink.
I am just not sure it is a.c. current.
 
  • #9
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I am using a lm224 operational amplifier. I always connect the diode to a limit resistor, I just forgot to draw it. Each resistor has a value of 2 kilohm. Each capacitor has a value of
120 microfarad, 6.8 microfarad or 100
Nanofarad. C1 equals c2. I use a 18650
Lithium ion cell as a power source.
 
  • #10
davenn
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I use a 18650
Lithium ion cell as a power source.

But your circuit doesn't show the battery connected to the power pins of the IC
so it cannot work
 
  • #11
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I forgot to draw that part. I always connect the power pins to the battery.
 
  • #12
Baluncore
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I always connect the power pins to the battery.
So you have a +3.6 volt battery. You connect that to supply the op-amp power. You ground the negative supply. But the sinewave output of a wien bridge oscillator swings about ground. That is not possible without some negative supply to the op-amp relative to ground.

Your circuit is definitely not a Wien Bridge oscillator. The reason it sometimes pulses is probably because you changed the circuit by moving R2 to give it positive feedback through C2.

Your inability to provide a full schematic wastes my time.
 
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  • #13
LvW
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Your inability to provide a full schematic wastes my time.
.........also my time!!
 
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  • #14
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What value should the gain be?
 
  • #15
Svein
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What value should the gain be?
The gain is critical, therefore you either need an automatic gain adjust or an amplitude limiter. I think the raw gain has to be greater than 3, but I haven't studied Wien oscillators for at least 30 years.
 
  • #16
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What you have drawn is not a Wien Bridge oscillator. Depending on the gain you have set, you may have created a "digital" oscillator (using the op-amp as a comparator). For info about the construction of a real Wien bridge oscillator, check out http://www.ecircuitcenter.com/Circuits/opwien/opwien.htm.
I tried building a wien bridge oscillator by coping the schematic in the website you gave me. Still unable to get the wien bridge oscillator to work. Any idea why it is not working?
245484
 
  • #17
Baluncore
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What is the power supply voltage to the op-amp ?
What type of op-amp ?
What part of the power supply is connected to ground ?
 
  • #18
LvW
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217
. Any idea why it is not working?
No - unless you give us the parts values.
Do you really expect an answer when the most important information is missing?
 
  • #19
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What is the power supply voltage to the op-amp ?
What type of op-amp ?
What part of the power supply is connected to ground ?
It is single power supply. The negative terminal of lithium ion cell is connected to ground. I am using a lm224 operational amplifier.
 
  • #20
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No - unless you give us the parts values.
Do you really expect an answer when the most important information is missing?
Each resistor is 1000 ohms. First each capacitor was 120 microfarad. Then I tried switching capacitors. Then I tried 100 nanofarad capacitors.
 
  • #21
Baluncore
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What part of the power supply is connected to ground ?
You ignored the critical question.
For an LM224 op-amp to work on a 3.6 volt supply, requires that the wien bridge ground must be attached to 1.1 volts above the B- terminal.
 
  • #22
Baluncore
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Use another amp in the quad op-amp package to make the common voltage.
245507
 
  • #23
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You ignored the critical question.
For an LM224 op-amp to work on a 3.6 volt supply, requires that the wien bridge ground must be attached to 1.1 volts above the B- terminal.
I don't know which terminal is the b-terminal?
 
  • #24
Baluncore
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The battery has two terminals.
One is positive, named B+. Called Vp on the simulation.
The other is negative, named B–. Called Vn on the simulation.
 
  • #25
257
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I think I am using the negative terminal as ground.
 

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