1Hz Oscillator using Op Amp

Thread Starter

DavidLander1995

Joined Jun 17, 2021
8
Hi,

I need help creating a 1Hz oscillator using an op amp and passive components, I’ve been trying but can’t get the theory to match the simulations.
Thanks.
 

neonstrobe

Joined May 15, 2009
178
How about showing us a circuit you have tried?
Is it not oscillating at all?
Or at the wrong frequency?
What are the RC values you have used?
Though I can offer some clues:
Oscillators have to have a minimum gain to start oscillating. Do youknow what that is for the Wien bridge?
Then when oscillations start they need some gain control to keep them from reaching the power rails. Simulators do reflect these issues, but tell us more!
 

Thread Starter

DavidLander1995

Joined Jun 17, 2021
8
How about showing us a circuit you have tried?
Is it not oscillating at all?
Or at the wrong frequency?
What are the RC values you have used?
Though I can offer some clues:
Oscillators have to have a minimum gain to start oscillating. Do youknow what that is for the Wien bridge?
Then when oscillations start they need some gain control to keep them from reaching the power rails. Simulators do reflect these issues, but tell us more!
Thanks for the reply:
I have attached my calculations which I used to work out the components, hopefully they are right.
Yeah the gain has to be over 3 doesn’t it... ideally 3.1

Thanks for the reply:
I have attached my calculations which I used to work out the components, hopefully they are right.
Yeah the gain has to be over 3 doesn’t it... ideally 3.1
 

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Audioguru again

Joined Oct 21, 2019
3,828
My simulation and everything I make do not use a lousy old (53 years old) 741 opamp.
This simple circuit does not have AGC so its output is usually clipping (not a sinewave).
 

Thread Starter

DavidLander1995

Joined Jun 17, 2021
8
My simulation and everything I make do not use a lousy old (53 years old) 741 opamp.
This simple circuit does not have AGC so its output is usually clipping (not a sinewave).
Hi thanks,

I will investigate using an alternative op - amp... the truth is this a new topic for me so still learning. I will try to sort it again to see if I can achieve 1Hz
 

Papabravo

Joined Feb 24, 2006
17,240
My simulation and everything I make do not use a lousy old (53 years old) 741 opamp.
This simple circuit does not have AGC so its output is usually clipping (not a sinewave).
Sorry. It is true that your opamp is not labeled. I thought you were duplicating the circuit of the TS for illustration purposes. I'm well aware of your opinions on the 741 and share them of course..
 

Ian0

Joined Aug 7, 2020
3,752
Sorry. It is true that your opamp is not labeled. I thought you were duplicating the circuit of the TS for illustration purposes. I'm well aware of your opinions on the 741 and share them of course..
Despite its age, I think it could manage 1Hz without slew limiting, though I wonder if a LM358 could manage it without crossover distortion!
 

Papabravo

Joined Feb 24, 2006
17,240
Despite its age, I think it could manage 1Hz without slew limiting, though I wonder if a LM358 could manage it without crossover distortion!
I think the point of the original simulation was to show that wrong component values had been selected, and without a confirmatory label on the schematic I did assume that a 741 model was being used. I think it might be able to manage 1Hz. if you catered to all of it's many needs.
 

Thread Starter

DavidLander1995

Joined Jun 17, 2021
8
Hi everyone,

just an update... I’ve been playing around with the components and atm I’ve got it at 10Hz, I’ve also changed from the 741 to the LM358AD.

still looking to bring it down to the 1Hz
 

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Ian0

Joined Aug 7, 2020
3,752
You have the non-inverting input connected to the wrong place. It goes to the junction of R3 and R4.
500Ω is way too low, and you will struggle to fine a non-polarised 30uF capacitor in real life.
 

Thread Starter

DavidLander1995

Joined Jun 17, 2021
8
Hi everyone,

just an update... I’ve been playing around with the components and atm I’ve got it at 10Hz, I’ve also changed from the 741 to the
You have the non-inverting input connected to the wrong place. It goes to the junction of R3 and R4.
500Ω is way too low, and you will struggle to fine a non-polarised 30uF capacitor in real life.
LM358AD.


Hi Ian, thanks for the advice.
I have changed it now, I have also carried out the calculations again to work out the values of the resistors based on a cap size or the 10uF that you suggested. Although the output doesn’t seem to oscillate now. It’s been running for 30s

I have attached the calculations and the simulations again.
Thanks
 

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neonstrobe

Joined May 15, 2009
178
The gain setting is critical with a high gain op-amp (even a 741, at low frequencies).
Try kick starting the oscillations by setting one of the capacitors in the timing bridge with an initial voltage (e.g. 0.5V)
Then watch the oscillations. If they die away increase the gain (reducing the 50k or increasing the 100k) in small amounts and repeat. If they clip to the rail voltages reduce the gain with opposite adjustments. You may need to trim the feedback ratio to three or four decimal places. Real oscillators will need amplitude stabilisation.
 

Audioguru again

Joined Oct 21, 2019
3,828
I do not know why your frequency is so low.
It takes the circuit a long time to begin oscillation because it is missing an automatic-gain-control (AGC) circuit (usually it uses a rectifier driving a Jfet) which gives it high gain to begin oscillation quickly then reduces the maximum output level to avoid clipping. Look it up.

LM358 dual and an LM324 quad opamps are the only ones I know that produce crossover distortion. The distortion can be eliminated if a load is added to a supply rail so that one of the output transistors operates in class-A.
 

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