Unable to get a Wien bridge oscillator to work

[David lopez]

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?

This a drawing of the circuit I am using.

 

[Svein]

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.

 

[LvW]

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?

 

[David lopez]

I consult an article on the internet. It
Show me a schematic and I used that.

 

[David lopez]

I have been unable to get the circuit
Svein showed me to work.

 

[Baluncore]

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?

 

[LvW]

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.

 

[David lopez]

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.

 

[David lopez]

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.

 

[davenn]

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

 

[David lopez]

I forgot to draw that part. I always connect the power pins to the battery.

 

[Baluncore]

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.

 

[LvW]

Your inability to provide a full schematic wastes my time.

...also my time!

 

[David lopez]

What value should the gain be?

 

[Svein]

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.

 

[David lopez]

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?

 

[Baluncore]

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 ?

 

[LvW]

. 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?

 

[David lopez]

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.

 

[David lopez]

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.

 

[Baluncore]

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.

 

[Baluncore]

Use another amp in the quad op-amp package to make the common voltage.

 

[David lopez]

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?

 

[Baluncore]

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.

 

[David lopez]

I think I am using the negative terminal as ground.

 

[Baluncore]

I think I am using the negative terminal as ground.

Then it cannot work, because the op-amp sinewave output cannot go outside the supply voltage, that is below B-.

You will need to build the left hand side of the circuit I posted. That will provide the common ground voltage for the oscillator. The oscillator output can then move between common – 1 volt and common + 1 volt.

 

[LvW]

Each resistor is 1000 ohms. First each capacitor was 120 microfarad. Then I tried switching capacitors. Then I tried 100 nanofarad capacitors.

Is it really a problem for you to show us the complete circuit with power supply and parts values?
Are you aware that the most critical part is - as far as the oscillation capability is concerned - the gain of the opamp (hence the feedback resistors), which is still unknown!

 

[Art Harrison]

A proven, working Wien bridge oscillator schematic is shown on page 29 at:
https://www.analog.com/media/en/technical-documentation/application-notes/an43f.pdf.

Use the parts suggested and a dual (positive and negative) 15 volt supply. The op amp need not be the relatively expensive LT1037; a LM741 or TL081 will work fine. But make sure that your op amp is rated for the dual 15 volt (30 volt total) supply voltage! The 327 lamp (used for amplitude stabilization) is a common type ubiquitous in the electronics industry for at least 50 years, and is still very easy to find, even at sources such as at Digi-Key.

This rendition of the Wein bridge has a very wide bandwidth; you will be able to achieve frequencies low enough to produce visible blinking rates for a LED by raising the values of the two 1600 ohm resistors to, for example, 470,000 ohms. However, connecting a LED directly to the output of this circuit will probably require some added parts to prevent inverse polarity across the LED, and provide it with the proper current.

Wien bridge oscillators are useful for producing sine waves with very low distortion, but are hardly a good way to simply blink a LED. If you want to blink a low-current led with a single, low-voltage power source (such as a 3 to 6 volt battery) then use one section of a hex Schmitt trigger inverter such as a CD40106B with a single capacitor and a resistor. I have some related circuits at https://www.theremin.us/Circuit_Library/led_sequencer.html

Reference: https://www.physicsforums.com/threads/unable-to-get-a-wien-bridge-oscillator-to-work.973148/

 

[Baluncore]

@Art Harrison
Welcome to PF.

This rendition of the Wein bridge has a very wide bandwidth; you will be able to achieve frequencies low enough to produce visible blinking rates for a LED by raising the values of the two 1600 ohm resistors to, for example, 470,000 ohms.

The problem with oscillators stabilised by filament lamps, is the thermal time constant of the filament. That limits the performance to about 20 Hz before distortion becomes a problem and the lamp filament oscillates in brightness.

 

[Art Harrison]

This particular circuit was thoroughly tested and produced excellent results at very low frequencies with the components shown. I did not test the circuit with a distortion analyzer, however, I used two 0.22 microfarad Mylar capacitors and two 1,000,000 ohm resistors to obtain a good-appearing sinewave of 0.72 hertz on an oscilloscope. Apparently, the thermal time constant of the type 327 lamp is long enough to accommodate even this very-low frequency. Referring to figure 40 in the Jim Williams' source article, he suggests four series-connected type 1891 lamps and 100 ohms for frequencies lower than 50 hertz.

I have a commercial Hewlett-Packard model 204D Wein bridge oscillator that uses incandescent lamps and has a lower-frequency limit of 5 Hertz. The manual for this oscillator sets that a typical distortion of 1% is obtainable at this frequency.

One precaution regarding the use of an incandescent lamp for Wein bridge oscillators is that the lamp filament, when subject to vibration, will cause modulations in the output. This is immediately apparent in the subject circuit when it is set up for the article's example of 1,000 Hertz. Otherwise, incandescent lamps are superb elements for the control of Wein bridge oscillators. the type 327, operating well-below visible incandescence, will potentially last for many decades without failure.

 

[Svein]

 

[Baluncore]

@Svein
I agree. The gate voltage control circuit of a FET can have a longer time constant than a filament globe, and that does reduce harmonic distortion at low frequencies.

 

[Art Harrison]

@Svein
I agree. The gate voltage control circuit of a FET can have a longer time constant than a filament globe, and that does reduce harmonic distortion at low frequencies.

Here's another FET-stabilized Wien bridge oscillator I designed for a pitch theremin, which is an electronic musical instrument:

https://www.theremin.us/Circuit_Library/wienbridge.htm

And here's another circuit I designed using two Wien bridge oscillators (to make a pitch theremin). In this circuit, operational transconductance amplifiers are the regulating elements:

file:///C:/Users/Arthur/Desktop/Theremins/203%20Theremin/203.html

I particularly like the second circuit, however, the operational transconductance amplifiers are generally only available as residual stock, and therefore not recommended for new designs.

 

[Baluncore]

And here's another circuit I designed using two Wien bridge oscillators

That link is to your C: hard drive.

 

[Art Harrison]

That link is to your C: hard drive.

This link should work: https://www.theremin.us/203/203.html