# Help with wien bridge diagram

Joined Jul 24, 2007
10
Hi
I'm very new to electronics, and I thought a fitting first project would be a Wien-bridge oscillator. Since I have a lm386 amplifier lying around, I thought I'd use the circuit discribed in the datasheet of this component (attached, see page 5). Now I have some questions about this diagram.
What kind of component is the round thing marked "ELDEMA CF-S-2158"?
What is $$R_{L}$$, $$V_{S}$$ and $$V_{O}$$?
What is the "Bypass"? What voltage should I use and where do i connect the output (speaker or whatever)?

Many thanks for help with answering these probably simple questions.

Joined Jul 24, 2007
10
Forgot the attachement...

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#### hgmjr

Joined Jan 28, 2005
9,027
Hi
I'm very new to electronics, and I thought a fitting first project would be a Wien-bridge oscillator. Since I have a lm386 amplifier lying around, I thought I'd use the circuit discribed in the datasheet of this component (attached, see page 5). Now I have some questions about this diagram.
What kind of component is the round thing marked "ELDEMA CF-S-2158"?
What is $$R_{L}$$, $$V_{S}$$ and $$V_{O}$$?
What is the "Bypass"? What voltage should I use and where do i connect the output (speaker or whatever)?

Many thanks for help with answering these probably simple questions.
The round thing is a light bulb. It is used in this application because it exihibits negative resistance.

Vs is the positive power supply input.

Vo is the output of the oscillator.

hgmjr

Joined Jul 24, 2007
10
ok, thanks
what kind of bulb can I use? The specified bulb seems to be hard to get, aswell as any bulb with the 3V 15mA specs. Can I use a bulb with higher voltage or higher current?

#### beenthere

Joined Apr 20, 2004
15,819
Mouser carries lamps and has no minimum order. It is possible to substitute bulbs with different ratings by experiment. The filament voltage should be no more than about 15, and the rated current should be no more than 40 ma. You just have to find a resistor for the feedback that works with the bulb, using more current - smaller resistor as the basis.

Joined Jul 24, 2007
10
I live in Sweden, so I'd rather not order from the US. I found 3V 10mA bulb in sweden though, do you think that might work?

Joined Jul 24, 2007
10
Thanks for the help everyone. Here are some images of the final construction, it's working perfectly.

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#### DanRilley

Joined Jan 13, 2008
107
This post is real old but maybe the poster still reads. Where do you buy bulbs from in Sweden? I'm also here and looking to complete the same project.

#### joseph.oneill

Joined Apr 21, 2021
1
Hi
I'm very new to electronics, and I thought a fitting first project would be a Wien-bridge oscillator. Since I have a lm386 amplifier lying around, I thought I'd use the circuit discribed in the datasheet of this component (attached, see page 5). Now I have some questions about this diagram.
What kind of component is the round thing marked "ELDEMA CF-S-2158"?
What is $$R_{L}$$, $$V_{S}$$ and $$V_{O}$$?
What is the "Bypass"? What voltage should I use and where do i connect the output (speaker or whatever)?

Many thanks for help with answering these probably simple questions.
Re SNAS545C –MAY 2004–REVISED MAY 2017 www.ti.com Product Folder Links: LM386 Submit Documentation Feedback Copyright © 2004–2017, Texas Instruments Incorporated 9.2.4 Low Distortion Power Wienbridge Oscillator
You are looking for a constant current device for this application. Yes a lamp was uses in the past but you can build aconstant current source with two transistors. Or you could try using an led driver like AL5809Q NEW PRODUCT AUTOMOTIVE COMPLIANT 60V Two Terminal Constant Current LED Driver PowerDI
https://docs.rs-online.com/ef32/0900766b81567f08.pdf
https://www.electronics-notes.com/a...transistor/active-constant-current-source.php
However itis is only for stability of the frequency and a potential devider (pot) will get this working while you try other methodes.