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XTAL

Posted on 2002-06-10
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Last Modified: 2010-04-26
HI
Can I change a crystal 1 MHZ with RC circuit if there any alternative circuit please, tell me so as to make my device work. If you have any documents about oscillator or links tell me about.
NOTE: I DON'T HAVE THIS CRYSTAL.
Regard  
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Question by:kadhim
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by:frache
ID: 7067607
No ... ( rc circuit).
1 Mhz crystal is the best way if you want a "good" (exact) clock generator.
You can find clock generator IC (Cypress for example) but you need also a Xtal ...
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by:frache
ID: 7067612
Give us more details about your circuit ...
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by:jhance
ID: 7067868
An RC network is NOT a good replacement for a crystal.  It's possible with an LC circuit but the results will be less than desirable.

Why do you want to do this?  1MHz crystals are common, easy to come by, and quite inexpensive.  You can probably find them free or close to it at a junk shop or HAMFest.

Anyway, most cyrstals are PARALLEL RESONANT and so a parallel LC circuit will give similar characteristics BUT at a MUCH MUCH lower "Q".  "Q" is the "peakiness" of the circuit and crystals are used because their "Q" is VERY high.  That's what makes them so good to use in an oscillator, since they peak so highly they run only at the resonant freq.  The problem with LC substitutes is stability, they need to be manually tuned to begin with and they drift due to temperature, humidity, age, etc.  Be prepared to go from a 1MHz that runs at +/- 1% to +/- 50% or more with an LC.

The freq. for a parallel LC circuit is: F = (2*PI)/SQRT(LC)

Now the trick is finding an available L and C (remember these are manufactured in standard values) that will run at about 1MHz.
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Author Comment

by:kadhim
ID: 7069648
Thanks ,frache & jhance.
The details about my circuit:
I want to input a voice into computer by codec and some ACC circuits that run at  about 1MHZ.
Please , jhance give me more details and internet topics.
Regaard.
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Author Comment

by:kadhim
ID: 7069701
Thanks ,frache & jhance.
The details about my circuit:
I want to input a voice into computer by codec and some ACC circuits that run at  about 1MHZ.
Please , jhance give me more details and internet topics.
Regaard.
0
 
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Expert Comment

by:jhance
ID: 7069803
I don't understand your problem.  You're designing and building a CODEC circuit (which DEPENDS on a rock-solid timebase for proper operation) but you want to substitute for a inexpensive crystal???  

Your premise makes no sense.
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Author Comment

by:kadhim
ID: 7070773
OK ..I'am in far country in Africa ,and I can not bring this item to my country before one month and I want to complete my design in this week.
thanks
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by:frache
ID: 7072210
There is perhaps a way to find a crystal in your country : try to find an old computer ...
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frache earned 300 total points
ID: 7072219
Here you can find a lot of information about oscillators :
http://www.epanorama.net/links/oscillator.html

But for your design, the best way is to find a crystal ...
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