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Old 1st July 2008, 01:54 AM   #11
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Go to the Linear Technology site and track down AN5. On page 8 is a simple wien bridge oscillator. The trick is using small light bulbs for stabilization. It can be done with other circuits, but they are way more trouble. For more on that, see the piece Jim Williams of LT wrote, "Max Wien, Mr. Hewlett, and a Rainy Sunday Afternoon". This is in his book, "Analog Circuit Design". Possibly a local library will have it or can get it. Another interesting route is to use the Analog Devices programmable oscillator chips. You'll need to do some software, but they go from near DC to near daylight, and the waveform quality is better than the chips of old, with their triangle-to-sine converters that always left little points on the waveform. Even my favorite Wavetek 185 sweep gen suffers slightly from that.
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Old 1st July 2008, 02:23 AM   #12
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mod_evil,

You need to reduce the value of R2 slightly, because the circuit gain in less than 3 the way it is. 3 is the ideal value, but it may nned to be higher because of component tolerances.

Rick
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Old 1st July 2008, 02:39 AM   #13
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A lamp bulb, can help me in every situations...

Now I tested my schematic with a lamp bulb with 40w. This is the smaller which I can get at this moment.

The Wein Bridge now seens okay.

How can I get a square wave from a senoidal wave?

Best Regards!
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Old 1st July 2008, 03:52 AM   #14
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by mod_evil
A lamp bulb, can help me in every situations...

Now I tested my schematic with a lamp bulb with 40w. This is the smaller which I can get at this moment.

The Wein Bridge now seens okay.

How can I get a square wave from a senoidal wave?

Best Regards!

A small night light bulb might be a bit better, but if you are getting a decent sinewave at LF then perhaps that 40W bulb is the ticket.

Use a comparator to generate a nice square wave.. Make the slicing level adjustable and you can vary the duty cycle.

The aforementioned article by Jim Williams is highly recommended. I do ATE hardware design and he is the absolute authority on extreme precision dc source A to D and D to A converters (how about 1ppm accuracy) amongst a lot other things. While I am gushing I think Bob Pease over at National is worth more than a casual read as well.
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Old 1st July 2008, 07:46 AM   #15
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Quote:
Originally posted by mod_evil
How can I get a square wave from a senoidal wave?
You can amplify it to >>0.6V and pass it through a diode gate i.e. diodes in antiparallel or 'back-to-back'.

w
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Old 1st July 2008, 02:12 PM   #16
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by wakibaki


You can amplify it to >>0.6V and pass it through a diode gate i.e. diodes in antiparallel or 'back-to-back'.

w

Diode clipping makes fairly dreadful looking square waves, ok if you need something quick and dirty, but not recommended if you want to measure slew rate or rise times.
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Old 1st July 2008, 02:33 PM   #17
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Use a comparator as Kevin suggested. Also ground the input to it when switching the output to sine. Otherwise the square wave may interfer and distort the sine.
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Old 1st July 2008, 02:50 PM   #18
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Yeah, but there are no issues with duty cycle and slicing, which is why I mentioned it, and you can always tidy things up with a bit of Schmidt trigger logic...

w
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Old 2nd July 2008, 12:11 AM   #19
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Quote:
Originally posted by kevinkr



Diode clipping makes fairly dreadful looking square waves, ok if you need something quick and dirty, but not recommended if you want to measure slew rate or rise times.
Friends,

I tested a IRF640, with a 120ohm resistor in the Gate to make the square wave from the sine.

In the low frequencies < 1khz the square wave converter is distorting the square wave.

I will put some photos about this.

But... Now it isn't working. It works when it wants. I haven't words to write about this.

The senoidal output seems okay.

Best Regards,
Felipe Navarro
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Old 2nd July 2008, 01:50 AM   #20
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Linear Tech has some great op-amp oscillator circuits. See the various application notes that Jim Williams has written. They show you how to build an AGC with off-the-shelf parts.

Probably the easiest (relatively speaking) high quality signal generator is the Bob Cordell which appeared in Audio in the early 1980's -- this was the design used for the Tektronix SG505 which is a truely great sig gen. You can follow up the Cordell oscillator with the new buffer from National Semiconductor for a device that you can test low impedance loads with.

Cordell's design is on his website.
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