+ Post New Thread
Results 1 to 9 of 9
  1. #1
    Member level 5
    Points: 757, Level: 6

    Join Date
    Nov 2016
    Posts
    81
    Helped
    0 / 0
    Points
    757
    Level
    6

    Very low frequency sine wave generation

    I need to generate low freq. sine waves between 0.1Hz up to 200Hz as precise as possible.
    I also want to control the freq. from the PC. I cannot use sound card because the audio port cannot output down to 0.1Hz as far as I know.

    All the voltage controlled chips are obsolete.
    XR2206, ICL8038, MAX038 ect.

    DDS are surface mount and complicated to program.

    Is there a way to generate good sine waves for this freq. range?

    I used a ICL8038. I send command to Arduino to control/vary its PWM output.
    Then the PWM output is coupled to an active filter which outputs an analog voltage.
    And this analog voltage couples to the ICL8036 sweep input to vary the freq.
    But the sine wave is a bit distorted and for a range 0.1Hz to 200Hz capacitor must be changed several times, I mean 0.1Hz to 10Hz possible but for a higher freq. range I need to change the cap.

    Is there any chip or circuit topology which can be employed. And it would be great if I could even simulate it.

    •   AltAdvertisment

        
       

  2. #2
    Super Moderator
    Points: 66,847, Level: 63
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    13,639
    Helped
    3122 / 3122
    Points
    66,847
    Level
    63

    Re: Very low frequency sine wave generation

    Hi,

    All calls for a DDS. Use it and learn to program it. It is not difficult.

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



  3. #3
    Member level 5
    Points: 757, Level: 6

    Join Date
    Nov 2016
    Posts
    81
    Helped
    0 / 0
    Points
    757
    Level
    6

    Re: Very low frequency sine wave generation

    Quote Originally Posted by KlausST View Post
    Hi,

    All calls for a DDS. Use it and learn to program it. It is not difficult.

    Klaus
    They are all surface mount. Do you have any recommendations for any model or module?
    I dont have any experience with them.



    •   AltAdvertisment

        
       

  4. #4
    Super Moderator
    Points: 66,847, Level: 63
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    13,639
    Helped
    3122 / 3122
    Points
    66,847
    Level
    63

    Re: Very low frequency sine wave generation

    Hi,

    What's exactly the problem with SMD?
    We use it since decades. And I hand solder smd prototypes since decades.

    Additionally there may be adapterboards, there may be evaluation kits, there are assembly houses...what else do you need?

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



    •   AltAdvertisment

        
       

  5. #5
    Advanced Member level 5
    Points: 37,256, Level: 47

    Join Date
    Mar 2008
    Location
    USA
    Posts
    6,012
    Helped
    1743 / 1743
    Points
    37,256
    Level
    47

    Re: Very low frequency sine wave generation

    I've built digital waveform synthesis from HCMOS gates, UV
    EPROMs and a poor man's RDAC. Would run out of steam at
    higher freqs (I was after ~1MBPS modulation waveform for
    a RF DDS research project).

    A small FPGA might be a good way to go, use CMOS I/Os with
    sensibly weighted resistors or a DAC resource if you have one.
    Should be adequate lookup table capacity I would think.



  6. #6
    Advanced Member level 4
    Points: 8,248, Level: 21
    d123's Avatar
    Join Date
    Jun 2015
    Posts
    1,464
    Helped
    338 / 338
    Points
    8,248
    Level
    21

    Re: Very low frequency sine wave generation

    Hi,

    IMHO, It doesn't matter if it's obsolete, it matters if it's available and fulfils the required function. ...And isn't overly expensive. I guess you want PDIP... Jaycar sell the XR2206, it's only $20... What about the XR2209 (8-pin version)? I recollect RS UK were selling them off at ~$6 each three years ago.

    Failing that, op amps can make sine waves. Look for AN-31 and browse section 2 for a couple of ideas, e.g.:

    Click image for larger version. 

Name:	sine wave generator op amp circuit collection an-31.JPG 
Views:	3 
Size:	39.7 KB 
ID:	149999

    There's also this version of AN-31 with more pages and less pictures on each of them for some reason...It must be the modernisation process. First is National Semiconductor copy, second is TI.

    This may provide some ideas, too: AN-263 Sine Wave Generation Techniques



  7. #7
    Member level 5
    Points: 757, Level: 6

    Join Date
    Nov 2016
    Posts
    81
    Helped
    0 / 0
    Points
    757
    Level
    6

    Re: Very low frequency sine wave generation

    Quote Originally Posted by d123 View Post
    Hi,

    IMHO, It doesn't matter if it's obsolete, it matters if it's available and fulfils the required function. ...And isn't overly expensive. I guess you want PDIP... Jaycar sell the XR2206, it's only $20... What about the XR2209 (8-pin version)? I recollect RS UK were selling them off at ~$6 each three years ago.

    Failing that, op amps can make sine waves. Look for AN-31 and browse section 2 for a couple of ideas, e.g.:

    Click image for larger version. 

Name:	sine wave generator op amp circuit collection an-31.JPG 
Views:	3 
Size:	39.7 KB 
ID:	149999

    There's also this version of AN-31 with more pages and less pictures on each of them for some reason...It must be the modernisation process. First is National Semiconductor copy, second is TI.

    This may provide some ideas, too: AN-263 Sine Wave Generation Techniques
    Thank you but I need to control the sine freq. by a voltage input not a poti or varying cap. Is that possible to do with your attached circuit?



    •   AltAdvertisment

        
       

  8. #8
    Super Moderator
    Points: 249,046, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    43,337
    Helped
    13176 / 13176
    Points
    249,046
    Level
    100

    Re: Very low frequency sine wave generation

    OTA based gm-C oscillator can be designed with voltage controlled frequency, e.g. using LM13700. But you need a magnitude control loop to achieve real low distortion. It's inconvenient for 0.1 Hz frequency, magnitude settling takes a long time. Digital oscillator (DDS) is definitely preferred for low frequency and high quality sine generation.



  9. #9
    Advanced Member level 5
    Points: 40,088, Level: 48
    Achievements:
    7 years registered
    LvW's Avatar
    Join Date
    May 2008
    Location
    Germany
    Posts
    5,742
    Helped
    1722 / 1722
    Points
    40,088
    Level
    48

    Re: Very low frequency sine wave generation

    I doubt if you will be able to realize a sinusoidal oscillator which can be tunes between 0.1 and 100 Hz (three decades).
    More than that, it is not a simple task to build an analog oscillator for a frequency as low as 0.1 Hz.
    My first approach: There are biquadratic structures (universal filters with 3 opamps) which allow pole frequncies down to 0.1 Hz.
    Of course, with suitable feedback these filters can be used as oscillators and - yes - the frequency can be tuned with a grounded resistor (may be replaced by a voltage-controlled FET-resistance).
    However, the tuniong range will be max. 1 decade.

    - - - Updated - - -

    Here is a link for a "very-low-frequency-oscillator".

    https://www.researchgate.net/publica...ow_Frequencies



--[[ ]]--