# Need help on sinewave oscillator

Discussion in 'The Projects Forum' started by munap, Dec 9, 2012.

1. ### munap Thread Starter Member

Nov 23, 2012
33
0
Greeting,

i'm making sinewave oscillator and i have problem on these situation :
1)please help me to change the frequency of the 1st circuit as attached to 50Hz( i have tried and cant get 50Hz exactly)

2)if the 1st circuit work at 50Hz, can i use the circuit as input to the another circuit for an example,as i attached the 2nd circuit(i have tried and the input voltage and frequency become low,anything can fix it?) Btw, the 2nd circuit i set the frequency at 50Hz.

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2. ### Wendy Moderator

Mar 24, 2008
20,735
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Have you thought of using a digital circuit with a filter? You can use a crystal oscillator, drop the frequency down to 50Hz, then use a simple filter to make a precision frequency/waveform.

Analog oscillators can be tweaked to be very close, but they drift over time.

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3. ### #12 Expert

Nov 30, 2010
16,026
6,540
You can cheat a little bit by adjusting the resistance on one tank circuit, but analog oscillators still drift across time. How perfect does the frequency have to be and how long does it have to stay that way?

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4. ### munap Thread Starter Member

Nov 23, 2012
33
0
Hello sir,

Sorry for my late reply, i'm newbie in electronic field and thanks for your guidance. So i have 2 choices here :

1) if i use digital circuit, could you please give me a tutorial how to make one that related to my circuit. Really appreciate it.

2) if i use analog circuit, the closest value to 50Hz i can get is 55.56Hz( i calculate in simulation, if theoretical, i do not know how calculate the frequency). I need the frequency exactly 50Hz because i want use the circuit as an input to another circuit which is the other circuit is rated at 50Hz. About the duration to keep oscillating, i prefer the longest one as long it doesnt affect the circuit operation. I'm really appreciate your kindness to help me sir.

5. ### Wendy Moderator

Mar 24, 2008
20,735
2,499
No problem with being new. No one is born knowing this stuff. Lets go through your materials and tools first, what test equipment do you have? A DVM counts.

What parts do you have access to? A 100Khz crystal, for example, would simplify things a bit, but is not necessary. Or could you get an off the shelf oscillator, such is used in PCs and other electronics.

Show us the circuit you would like to build, the one you could not tweak using a simulator. You will have to put variable components into whatever you build most likely, it is entirely possible the circuit you want to build will work just fine with something as simple as a potentiometer. As I said earlier, just because you get the frequency right once does not mean it will not drift though.

Reading between the line I suspect you are wanting to make an inverter, or a clock for a digital clock or something similar. If you tell us your end goal it can simplify things all around.

Note: On the first circuit play with resistor values. Move them up and down 10Ω steps. That will move the frequency, and you will never be able to match components to theoretical values anyhow, which is why we have variable components.

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6. ### munap Thread Starter Member

Nov 23, 2012
33
0
Hello sir,

You are right sir,i'm building an inverter which is dc to ac with 3 phase sinewave.
This is my 3rd circuit sir because the other 2 previous circuits was a unable to generate stable sinewave and alot of distortion.

I got portable oscillator (Parallax Usb Oscillator) on myside. About the crystal, i never see real one, maybe i will go to electronic shop to get one of it. For the 1st circuit, i manage to get 50Hz but i want use the 1st circuit as an input to my 2nd circuit (as mentioned in first comment), the problem is the signal of voltage will getting low over time, like dying signal and at the end, the signal just die.

I will go with the 1st choice which is to use digital circuit but i'm do not know the building. Could you explain a bit sir. Really appreciate it and thanks in advance.

7. ### munap Thread Starter Member

Nov 23, 2012
33
0
Hello sir,

i have found some application note from MAXIM. The note talks about digital circuit from square wave generated by crystal to sine wave. In the note, the crystal was used 8MHz, so is that possible to change the crystal to smaller value so at the output, i could get 50Hz. I really appreciate your kindness sir. I attached the application note.

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8. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
655
How do you plan to use sine waves in a 3 phase inverter? Do you have a schematic, or a block diagram?

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9. ### munap Thread Starter Member

Nov 23, 2012
33
0
Hello sir,

I planned to use the sine wave into 3 phase inverter circuit as i attached sir. Notice that the input supply for the 3 phase inverter is ac voltage with 50Hz frequency. I wish to change the input supply with the sine wave circuit. Really appreciate the time you spend for this silly request sir. I'm also sorry that my simulation quite messy.

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10. ### Audioguru New Member

Dec 20, 2007
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Your simple circuit produces square-waves, not sine-waves because it has nothing to limit the output level to keep the opamps from clipping.

An inverter has outputs that are 120V RMS or 230V RMS at many Amps.
Your circuit is not an inverter because its outputs are only 20V peak-to-peak at a current of only 20mA.
Are you going to use a high power audio amplifier that gets VERY hot and wastes a lot of electricity from the battery?

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11. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
655
But what will you do with the outputs? You can't drive a 3 phase motor, unless it was extremely tiny.

I added the quadrature oscillator in Figure 15-20 of the TI sine wave oscillators application note to your phase shifter, and ran some simulations. See the attachments. It works well in simulations. I have not tested it in hardware.
Note that, if you build this in hardware, you will need to add a 100nF power supply decoupling capacitor from each op amp power pin to ground, or you may get unwanted high frequency oscillations.

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• ###### Three phase sinewave generator.asc
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12. ### munap Thread Starter Member

Nov 23, 2012
33
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Hello sir,

At the first glance, i was thought to runs a 3 phase motor if i succeed build my 3 phase inverter but things become unpredictable when my cost limitation( i really dont mind to spend a little much but its not my decision ) in this project. So instead of build real 3 phase inverter, i have to change my scope of project and build a 3 phase sine wave generator.

I know the circuit couldnt runs 3 phase motor or be used for other 3 phase application. My other idea to put transformer at each of phase of the 3 phase sine wave generator but once again, its a silly idea i guess and i have to find second-hand transformer(no idea how to get it) to reduce expenses.

Lastly,i have decided to narrow the scope of project by doing the simulation and for the hardware output, i just use oscilloscope to prove the idea.

Really thanks sir for helping me solve my problem. I guess, i just need to build dual supply for the next step and i'll post my complete project in here. Once again, really appreciate your kindness for helping me sir, thanks a lot.

13. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
655
Transformers wouldn't help you drive a motor. The op amps can only drive a few milliwatts each.

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14. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
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The op amps have feedback around them, and the input signal is within the rails.

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15. ### munap Thread Starter Member

Nov 23, 2012
33
0
Hello sir,

Thanks for the explanation sir, i will stay on the track for now.

16. ### Audioguru New Member

Dec 20, 2007
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I looked at the Oscillator title of this thread instead of looking at the schematic of the phase-shifter.

17. ### munap Thread Starter Member

Nov 23, 2012
33
0
Hello all,i have done the hardware circuit but i have problem on these things :

1)phase not shifted for 120 degree and 240 degree, all the phases have same degree
2)eventhough i got the output but i.c TL074CN seems like doesnt function at all, i have check the supply

I attched the output,btw i'm using portable oscilloscope (Parallax USB Oscilloscpe)

Hope any could give comment and suggest, thanks.

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18. ### Ron H AAC Fanatic!

Apr 14, 2005
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Is your circuit identical to the one I posted? If not, post your schematic.

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19. ### munap Thread Starter Member

Nov 23, 2012
33
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Hello sir,

Ya,i'm using the same schematic, all the phases doest not shifted.

20. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
655
Then you have something wrong. I suspect the phase shift network U7, R3, C1. Check for correct connection and correct values.

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