Help needed to identify a wave without using any Graphical means

Discussion in 'The Projects Forum' started by APDEV, Jun 6, 2014.

  1. APDEV

    Thread Starter New Member

    May 30, 2014
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    Can anybody say me how to identify a sine wave and square wave seperately without using any graphical means such as an Oscilloscope trace ???

    I am in the middle making a sine wave inverter.... The problem i am facing here is that;
    Since i do not have an Oscilloscope display with me, i am not able to say whether the output waves derived from each stage ( say PWM stage, Square wave generator stage, inverter output etc.. ) is a particular wave or not that is really intended to be.
    The oscilloscope display costs more than 15,000 rupees.
    At that price i can buy more than 10 inverters....
    The portable displays also costs more than 8000 rupees.

    I am making a pure sine wave inverter ( circuit is given as attachment )... Have to ensure whether the wave generated at its output is the modified sine wave or just a square wave...
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    there is nothing in your circuit that would make a sine wave, only square waves. your only using on off switching, not smoothing anything.
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    Well you could easily build yourself a transient digitizer in the inverter with a microcontroller. You would need one with an A/D converter and a serial UART. You sample the output waveform and send the samples to a PC. Then use the OpenOffice spreadsheet program to make a graph. That is how I would do it on a shoestring.

    More exotically you could use a DSP to do an FFT of the output and look at the harmonic content. A sinewave will have a single peak at the fundamental frequency. A squarewave will have a peak at the fundamental and a rich set of harmonics.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Without an oscilloscope you will not easily be able to tell what the output waveform is, or if the FETs are switching cleanly. As the 4047 can source/sink very limited current you my find that without a gate-driver stage between the 4047 and the FET gates the FETs do not switch cleanly at 50/60Hz. This would waste power and could lead to their over-heating.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    there are also articals and projects for using pc sound boards to display waveforms and harmonic content. google can be your friend.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    I think it may be some kind of PWM circuit to approximate a sine-wave.
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    You can use the LINE INPUT of the sound card on your computer to turn your PC into an oscilloscope in order to examine waveforms at audio frequencies.
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
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    wouldnt a synthesized sine wave generated by pwm be a bit distorted to use as a supply for an audio preamp? there is no smoothing of the waveform in the above circuit.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    Where is an audio preamp mentioned? :confused:
     
  10. alfacliff

    Well-Known Member

    Dec 13, 2013
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    he didnt, but there are things to be ran from sine wave inverters that do require sine waves, not pwm sinthesized "sine waves" we use a lot of variable frequency drives arund here, and the sinthesized waves sometimes have to be smoothed to prevent audible noise in motors, which can lead to heat, and heating in conduit.
     
  11. APDEV

    Thread Starter New Member

    May 30, 2014
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    Thank you very much friends for replying to ma thread....
    Someone made a comment that this inverter can not be a pure sine wave one ? How it could be possible to say that ? Have you pictured out all the portions of the figure ?


    The IC 4047 section remains basically the same and is configured in its normal free running multivibrator mode with its output extended with the mosfet/transformer stage for the required 12V to the AC mains conversion.

    The IC 4047 generates the usual square waves to the connected mosfets creating a mains output at the secondary of the transformer which is also in the form of square wave AC.

    The integration of the two 555 IC to the above stage completely transforms the output into a pure sine wave AC. The following explanation reveals the secret behind the IC555 functioning for the above.

    Referring to the 4047 pure sine wave inverer circuit , we can see two identical IC 555 stages, wherein the left section functions as a current controlled sawtooth generator while the right hand side section as a current controlled PWM generator.

    The triggering of both the 555 ICs are derived from the oscillator output readily available across pin#13 of IC 4047. This frequency would be 100Hz if the inverter is intended for 50Hz operations, and 120Hz for 60Hz applications
    .

    The left 555 section generates a constant sawtooth wave across its capacitor which is fed to the modulating input of the IC2 555 where this sawtooth signal is compared with the high frequency signal from pin3 of IC1 555 creating the required pure sine wave equivalent PWM at pin#3 of 555 IC2.

    The above PWM is directly applied to the gates of the mosfets. so that the square pulses here generated through pin10/11 of IC4047 gets chopped and "carved" as per the applied PWMs.

    The resulting output to the transformer also causes a pure sine wave to be stepped up at the mains AC secondary output of the transformer.
     
  12. APDEV

    Thread Starter New Member

    May 30, 2014
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    ALSO CAN ANYONE SUGGEST ME A CIRCUIT TO EFFECTIVELY CONNECT THE OUTPUT OF THE INVERTER TO THE AUDIO JACK OF THE LAPTOP to have a display of the output wave form by using the GOLDWAVE SOFTWARE ?
     
  13. crutschow

    Expert

    Mar 14, 2008
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    I read your extensive explanation but still don't see how your circuit can generate a sinewave since there is no sinewave oscillator in that circuit. :confused: I simulated the circuit in LTspice and also saw no signs of a sinewave in the output (of course I had to guess at some of the circuit values that were not given so that could be a factor. You might include those.). It's possible the circuit may be attempting to integrate a triangle-wave (not a saw-tooth) which gives a quasi-sinewave but that's not a "pure" sinewave.
     
    APDEV likes this.
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    To connect the output of the inverter to the audio input of a PC all you need is an attenuator. For a 230V RMS output (350V peak) the attenuator should provide at least ~ 1000:1 attenuation factor. It could e.g. consist of a 2 x 470k resistors (each 250V rated) and 1 x 1k resistor in series. (The two 470k resistors would share the high voltage).
    Because of the closeness of the inverter output envelope frequency to the lower bandwidth limit of a typical PC sound card there will be waveform distortion.
    Here's what the sound card output signal could look like for a modified-sinewave (I prefer to call it a modified-squarewave) input:
     
    Last edited: Jun 7, 2014
  15. Brownout

    Well-Known Member

    Jan 10, 2012
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    How much is 15,000 rupees? Spark Fun has a little LCD scope kit for about 50 bucks. Other than that, I don't know a way to evaluate a wave.
     
  16. APDEV

    Thread Starter New Member

    May 30, 2014
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    I am sorry... I have used the notation of INDIAN currency...
    15000 rupees means about 250 American Dollars
     
  17. Brownout

    Well-Known Member

    Jan 10, 2012
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    Do you have a microcontroller with an A/D converter? I have a preliminary design for an oscilloscope using a microcontroller, but you would need to finish it, which means a lot of experimentation to do.
     
  18. APDEV

    Thread Starter New Member

    May 30, 2014
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    Thank you Crutschow for replyiing to ma thread.
    Could you please post the Stimulated diagram of my circuit that you did in LTspice here ?
    If possible plz attach the print screen preview...
    I don't know how to add 555 Ics in LTspice...

    Do you know any other best stimulation software that can be used for all types of circuits such as digital and analog ??
     
  19. crutschow

    Expert

    Mar 14, 2008
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    Attached is a shot of my simulation and the simulation file. It doesn't include the output transistors but those aren't needed to do the simulation.

    The simulation does require the addition of the CD4000.lib, the CD4047b.sub, and the potentiometer.lib files. If you don't have those I can help you install them. The 555's should already be there I think (in the Misc library).

    Ltspice is used by many on these forums. There may be other good free Spice programs but I'm not that familiar with them. If you can spend some money, then there are numerous other good simulation programs available.

    PWM Sinewave.gif
    View attachment PWM Sinewave.asc
     
  20. APDEV

    Thread Starter New Member

    May 30, 2014
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    Thank you very much Crutschow for helping me...

    But a doubt still remains there...

    CAN ALL THESE STIMULATION SOFTWARES ( especially the LTspice ) generate the exact wave form as expected ???
     
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