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I'm making a function generator which works in the audio range for a college project. I'm not allowed to use microcontrollers or any digital chips. So I'm using a Wien Bridge oscillator with a pot to generate variable sine wave. It is followed by a Schmitt trigger to generate square waves and finally an integrator to get triangle wave. I found this schematic on the web for the Wein bridge:

Schematic

Could you replace the two variable 100k pots by a single pot? If not, is it possible to somehow mechanically (or electrically) gang the two different 100k pots? I'm trying to avoid using a single double-ganged-potentiometer to save cost.

I would like my final design to have only two pots. One for frequency and one for amplitude.

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  • \$\begingroup\$ Can you use a 555 timer? \$\endgroup\$ Jul 31 '14 at 16:36
  • \$\begingroup\$ yeah that was my first choice.i can easily get a square or triangle wave with 555.the main problem is with sine wave.i would need to filter the harmonics out of a square wave.that is difficult since i need variable frequency \$\endgroup\$ Jul 31 '14 at 16:50
  • \$\begingroup\$ OK, I posted this the other day. It needs a dual power supply, but it has much better gain control than your circuit. dropbox.com/s/lmso5zx69g2l1lc/DSCF0047.JPG \$\endgroup\$ Jul 31 '14 at 16:54
  • \$\begingroup\$ Thanks.But this would still need two pots I guess?Looks like i have to use a ganged pot. \$\endgroup\$ Jul 31 '14 at 17:05
  • \$\begingroup\$ Or you could do like HP did in their venerable 204 series of oscillators and use a ganged variable capacitor. \$\endgroup\$ Jul 31 '14 at 18:39
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Are you forced to use the WIEN oscillator (named after Max WIEN) topology ? There are other oscillator types with single-element control - however with two operational amplifiers.

Here is a corresponding link: http://m.eet.com/media/1143038/17995-82202di.pdf

I like to mention that for frequency tuning you only have to tune one single grounded resistor. More than that, the quality of the output signal (THD) - for most applications - will be sufficient, even without additional amplitude control mechanism.

EDIT: To all who also are interested in the update of the referenced paper: Try this link (I hope it works) and search for "A novel harmonic Oscillator: GIC Resonator" : https://www.researchgate.net/profile/Lutz_Von_Wangenheim/publications

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  • \$\begingroup\$ No.Any oscillator with variable sine frequency will do .Could you name or post a few alternatives \$\endgroup\$ Jul 31 '14 at 17:42
  • \$\begingroup\$ I have a pdf doc on my hard disc - but I don´t know how to submit. Any advice? \$\endgroup\$
    – LvW
    Jul 31 '14 at 17:46
  • \$\begingroup\$ I don't know.i'm new here.You could mail me at kishoresaldanha@gmail.com . \$\endgroup\$ Jul 31 '14 at 17:53
  • \$\begingroup\$ I have updated my answer above with a link to a corresponding article. However, I have an updated version which I will send to you via mail, OK? \$\endgroup\$
    – LvW
    Jul 31 '14 at 18:23
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Well you could probably rig something up to turn both pots at the same time. But I think a dual ganged pot will be cheaper. I've used a Bourns dual ganged pot ~$5. http://octopart.com/partsearch#!?q=91a2ab28b
Not the first hit.

You can also use a dual switch. Or maybe a digital pot?

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