# Help with wien bridge diagram

Discussion in 'The Projects Forum' started by hadoque, Jul 24, 2007.

Jul 24, 2007
10
0
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.

Jul 24, 2007
10
0
Forgot the attachement...

File size:
264.4 KB
Views:
69
3. ### hgmjr Retired Moderator

Jan 28, 2005
9,030
218
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

Jul 24, 2007
10
0
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?

Jul 17, 2007
22,202
1,793
6. ### beenthere Retired Moderator

Apr 20, 2004
15,815
293
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.

Jul 24, 2007
10
0
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?

Jul 24, 2007
10
0
Thanks for the help everyone. Here are some images of the final construction, it's working perfectly.

File size:
53.2 KB
Views:
148
File size:
32.2 KB
Views:
128
File size:
29.1 KB
Views:
112
9. ### DanRilley Senior Member

Jan 13, 2008
107
0
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.

May 11, 2009
5,939
1,227