Very low frequency sine wave generation

[doncarlosalbatros]

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.

 

[KlausST]

Hi,

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

Klaus

 

[doncarlosalbatros]

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.

 

[KlausST]

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

 

[dick_freebird]

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.

 

[d123]

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 **broken link removed** and browse section 2 for a couple of ideas, e.g.:



There's also **broken link removed** 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

 

[doncarlosalbatros]

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 **broken link removed** and browse section 2 for a couple of ideas, e.g.:

View attachment 149999

There's also **broken link removed** 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?

 

[FvM]

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.

 

[LvW]

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.

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