I have tried building a phase shift oscillator, but it won't work

berkeman

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What power supply rails are you using with the opamp? Which opamp is it? Do you have an oscilloscope to use for debugging?

If you do have an oscilloscope, draw the circuit diagram with the pin numbers shown on the opamp, and use the oscilloscope to probe each of the nodes in the circuit. Write down the DC voltage that you find at each node, and scan and attach that drawing to a reply here. That will help us a lot to guide you to get the circuit working.

What is your target oscillation frequency, BTW?
 
I don't have an oscilloscope. I use a
18650 Lithium ion cell as a power source. I am trying to get the phase shift oscillator to oscillate at all.
 

berkeman

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18650 Lithium ion cell
That's a 3.6V battery. I doubt you could get that circuit to work with just a single supply voltage anyway, especially one so low.

244944


That circuit would appear to want to oscillate around ground (given the biasing), so you will need split supply voltages to give the opamp compliance with the power supply rails. Maybe for an experiment, try two 9V batteries hooked in series to give you +/- 9V power supplies to the opamp.

You also did not say yet which opamp you are using, or what component values you chose for what oscillation frequency. Did you build this on a plug-in type breadboard?

I'm guessing this is supposed to oscillate in the audible range? Otherwise, how will you tell if it's working if you don't have an oscilloscope?
 

davenn

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But it won't work.
How do you troubleshoot this?

Probably because you didn't connect the battery to the power pins of the IC
so it cannot work
 

tech99

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Circuit diagrams often do not give a beginner the details of how to connect the batteries. Also the load must be fairly high resistance, a few hundred Ohms, not a 35 Ohm speaker for instance.
 

davenn

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Circuit diagrams often do not give a beginner the details of how to connect the batteries.

yeah and that's where, I'm suggesting, he's probably tripped up in both his threads
 
I am using a lm244 operational amplifier. I made sure the ground pin
Was connected to the negative terminal. I made sure the voltage supply pin was connected to the Positive terminal. The 18650 lithium ion cell I use have a measured voltage of 4.2 volts roughly. I use a single supply configuration. Each resistor has a value of one kilohm. C1 is 120 μf, c2 is 120 μf, c3 is 6.8 μf.
 
I can build a frequency divider to measure the frequency.
 

berkeman

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I am using a lm244 operational amplifier.
Although the input voltage range of the LM224 family of opamps includes ground, it does not tolerate signals that are below ground. Your circuit will oscillate with the average voltage level at ground, so the circuit needs to be able to work with signals that swing below ground.

That means you need split power supplies for this to work. You need two power rails, like the +/- 9V supplies that I already mentioned. Do you understand why this is needed?

And as mentioned by others, be careful not to load the output of this first opamp too much. It would be best to add a follower opamp buffer (use another of the opamps in that quad IC package) before driving any frequency divider or speaker circuits.
 
Should I use a different operational amplifier? And can the lm224 swing
Below ground?
 

davenn

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Was connected to the negative terminal. I made sure the voltage supply pin was connected to the Positive terminal.
Hopefully not the + and - terminals as shown in those circuits
They are not the power supply pins

the chip datasheet shows the power connections

LM224 pins.JPG


Are you really using a LM244 or is it the LM224 as @berkeman said in his response ?

Why did you choose a LM224 they are a quad op-amp, 4 op-amps in one package ?
Why not use just a single op-amp package and make things easier to work out ?
Less chance of doing incorrect wiring
 
That was a typo. I am using the lm224.
And I have the datasheet. I use the datasheet to make sure the wiring is
Correct.
 
Do You need two positive rails and two
Negative rails to provide split power
Supplies? I have a breadboard with two positive rails and two negative rails.
 

berkeman

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I have a breadboard with two positive rails and two negative rails.
What does that mean? Can you post a picture? Does it mean that the breadboard you have can support up to 4 power supply voltages plus ground?
Do You need two positive rails and two
Negative rails to provide split power
Supplies?
You should connect your split +/- 9V power supply voltages to the +/- power input pins of the LM324/whatever. If you were using all 4 opamps in the package, it would look something like this (this is not an oscillator circuit, and you should connect -9V to the IC pin 11 instead of the ground shown in this schematic):


244993



When you use only one opamp out of a quad IC package, it is best practice to tie the other 3 opamps off in a way that minimizes noise and power consumption. You can connect them as followers with ground at their + inputs, for example.
 
Last edited:
244995


This breadboard can support two
Different voltages.
Do you connect the negative terminal of one battery to the Positive
Terminal of the other battery to make a split power supply?
 

berkeman

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Ah, yes. Assuming that each of those outside 4 columns are connected vertically, I usually will use the inside two for ground connections (and tie those two columns together at one end), and use the outside two columns for my +/- supply voltages. If I need to support +5V and also +/-12V in the same circuit, then I only get one ground column.

Here is how you connect two 9V batteries to give the split supplies that you need for your oscillator circuit:


245000
 
So you connect the Positive terminal
From battery a to ground and connect
The negative terminal from battery b to the same. Ground
 

sophiecentaur

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Circuit diagrams often do not give a beginner the details of how to connect the batteries. Also the load must be fairly high resistance, a few hundred Ohms, not a 35 Ohm speaker for instance.
You are right but beginners should realise that they are, in fact, beginners and start from the beginning of the subject. All those bits of knowledge that we get, on the way through a life using electronics, are worth something and it is foolhardy to try to leap into a subject half way through and expect it all to 'go right'.
I blame the dreaded simulators which try hard to make your circuit work by assuming the right supply volts and appropriate supply rail decoupling etc. etc.. Real components are not mathematical functions but the message for beginners seems to be otherwise.
 

sophiecentaur

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I suspect that the OP is trying to achieve an Electronics Course by means of the Q and A system. It ain't going to work, I'm afraid.
 
So I connect one voltage to the inverting Terminal and connect the other voltage to the noninverting terminal?
 

Averagesupernova

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So I connect one voltage to the inverting Terminal and connect the other voltage to the noninverting terminal?
This makes no sense in and of itself. Whatever thought you had prior to making this post we cannot determine. We cannot read your mind. Are you still talking about split power supplies? You need to do better. Inverting and noninverting are inputs and are not considered part of the power supply rails.
 

sophiecentaur

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So I connect one voltage to the inverting Terminal and connect the other voltage to the noninverting terminal?
This just amplifies the point I made earlier about jumping into a subject too far. Calm down and start at the beginning; save yourself time, overall.
PS Why do you need a phase shift oscillator? That's a pretty sophisticated function for a circuit - much harder than connecting up a power supply to an integrated circuit.
 
You said start at the beginning. where is the beginner? I need a phase shift oscillator, because I want make a circuit that generates ac current. Where should I start learning
To generate ac current?
 

berkeman

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I want make a circuit that generates ac current
There are lots of ways to generate an AC current. What frequency range? What amplitude? What is the load that you want too drive? Do you need a sine wave, or would a square wave or triangle wave work for your application?
 

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