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Old 7th February 2004, 01:58 AM   #11
jcx is online now jcx  United States
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the data sheet doesn't show the schmidt trigger oscillator that gives near 50% duty cycle without having to change multiple resistor values in the "normal" astable oscillator circuit - tie thres and trig inputs together with a resistor/pot to output, and a cap to gnd from the inputs; to cover 3 decades of freq it is a good idea to switch in different C values

the schmidt trigger oscillator will be within a few % of 50% duty cycle, for better symmetry the classic solution is to use a digital divide by 2 flip-flop such as a 74HC74 on the oscillator output to get good symmetry and very square corners - the 74 AC74 can give ~ 50 ohm output Z as well
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Old 7th February 2004, 04:29 AM   #12
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Default Maybe I need some edumactin'

If you made an oscillator with a 555 chip, wouldn't you just get a pulsed DC? The negative part of the square wave would be a period of zero volts and no electrons flowing in the negative direction.

Is there some device that would discharge some stored energy and cause electrons to go back in the other direction and create a true square wave?

Just wondering,

Aud_Mot
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Old 7th February 2004, 09:43 AM   #13
Faber is offline Faber  Italy
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my 2Cents:

I'm building a signal generator using the xr8038. It provides simultaneously triangle (or sawthoot), sine and square wave. It doesnt cost so much (I find it at 3.25$ each) and permits to have a good signal with a simple circuit.

Bye!
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Old 7th February 2004, 11:23 AM   #14
lukio is offline lukio  Indonesia
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Default Signal Generator

Hi..

Why don't you use some free software that can make any wave ....but you should have SB card in your computer


just wondering..


Lukio

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Old 7th February 2004, 11:25 AM   #15
sss is offline sss  Israel
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Quote:
Originally posted by jcx
for better symmetry the classic solution is to use a digital divide by 2 flip-flop such as a 74HC74 on the oscillator output to get good symmetry and very square corners - the 74 AC74 can give ~ 50 ohm output Z as well
thanx jcx i already thought of that
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Old 7th February 2004, 11:29 AM   #16
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Default Re: Maybe I need some edumactin'

Quote:
Originally posted by Aud_Mot


Is there some device that would discharge some stored energy and cause electrons to go back in the other direction and create a true square wave?

Just wondering,

Aud_Mot [/B]
YES! We call such a device a “Capacitor”

Hook up a 47uF capacitor to the output of the 555 and a 10k resistor to gnd. If you use a potmeter for the resistor you have a volume control as well. You can best use a C-Mos 555 like the TLC555. These are a bit faster and due to the higher input impedances are better suited to low frequencies.

Cheers
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Old 7th February 2004, 12:24 PM   #17
SY is offline SY  United States
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Default Re: Signal Generator

Quote:
Originally posted by lukio
Hi..

Why don't you use some free software that can make any wave ....but you should have SB card in your computer


just wondering..
You can't really get a good square wave from sound cards because of the sharp bandlimiting. At higher frequencies, there's always ripple on the tops and bottoms or overshoot on the leading edge. A 555 or a function gen chip is a much better solution.
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Old 22nd December 2004, 12:17 PM   #18
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Faber,

You mention that you can get the XR8038 for $3, can you tell us where exactly as I've searched in vain.

Thanks

RV
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Old 22nd December 2004, 12:56 PM   #19
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This one will do the trick with just a PSU, two resistors (for tuneablility substitute one of them by a pot) and a capacitor added:

http://www.national.com/ds/CD/CD4020BC.pdf

=> look at the 4060 on this datasheet

Regards

Charles
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Old 23rd December 2004, 08:29 AM   #20
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