1
\$\begingroup\$

I'm looking to create several sine waves on a single circuit. All must be under 20Khz frequency and each must be unique. Mostly it will be 5-10 frequencies needed.

As I found - almost all crystal oscillator are in Mhz frequencies and only one kind is 32Khz (which is still too high).

I should be able to get this wave on the other side using FFT.

Ideas? :)

Thanks

\$\endgroup\$
3
  • 2
    \$\begingroup\$ How about the expected spectral purity of each sine wave? That parameter could lead to different solutions. \$\endgroup\$
    – Mario Vernari
    Commented Jul 21, 2011 at 11:37
  • 1
    \$\begingroup\$ Do you want the frequencies to be fixed or adjustable? \$\endgroup\$
    – Jim
    Commented Jul 21, 2011 at 15:23
  • 1
    \$\begingroup\$ What's important to you? Frequency stability? Frequency accuracy? (5.000000 kHz) Signal to noise ratio? Distortion? Are you doing multitone testing? \$\endgroup\$
    – endolith
    Commented Jul 21, 2011 at 16:48

2 Answers 2

Reset to default
0
\$\begingroup\$

You could easilly divide the 32KHz crystal frequency with a Binary Counter (such as the 4040) to give 16KHz, 8KHz, 4KHz, 2KHz, 1KHz, 500Hz, etc...

Then some clever filtering can create a sine(ish) wave from each of those square waves.

\$\endgroup\$
13
  • 2
    \$\begingroup\$ Then you can better start from a 12MHz crystal. Very common value, and many more dividers. These are the first multiples of 1kHz you can get from 12MHz: 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 16, 20, 24, 25, 30, 32, 40, 48, 50, 60, 75, 80, 96, 100,... \$\endgroup\$
    – stevenvh
    Commented Jul 21, 2011 at 10:55
  • \$\begingroup\$ Also, a 32kHz crystal is actually 32.768kHz, so you don't get the nicely round numbers from your answer. \$\endgroup\$
    – stevenvh
    Commented Jul 21, 2011 at 11:57
  • 1
    \$\begingroup\$ You get nice round binary numbers ;) 16,384Hz, 8,192Hz, 4,096Hz, 2,048Hz, 1,024Hz, 512Hz... \$\endgroup\$
    – Majenko
    Commented Jul 21, 2011 at 12:03
  • 2
    \$\begingroup\$ Yes, but for frequencies binary doesn't make sense like it does in addressing, for instance. Note that most of the time the 32.768kHz is just used to get a 1Hz signal. (yes, I noticed the smiley!) \$\endgroup\$
    – stevenvh
    Commented Jul 21, 2011 at 12:55
  • 2
    \$\begingroup\$ @roman - What Matt didn't tell you is that it's not that easy to filter out a sine from a square wave, especially not when it has to be done for multiple frequencies. I'm going to leave this to him to answer :-). (The DDS would have created a nice sine) \$\endgroup\$
    – stevenvh
    Commented Jul 21, 2011 at 15:08
6
\$\begingroup\$

Similar questions were asked here and here.

In this answer I talk about DDS, direct digital synthesis, which has replaced classical analog oscillators like Wien bridge. The DDS technique is crystal-based so has the same stability and accuracy.
Here you'll find a design for a simple DDS. DDSs which use special function ICs typically achieve a wide frequency range with very high frequency resolution.

\$\endgroup\$
1
  • \$\begingroup\$ Sadly, your link for the simple DDS design is dead :( \$\endgroup\$
    – Gallifreyan
    Commented Dec 13, 2019 at 12:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.