### Author Topic: Crystal oscilators  (Read 2333 times)

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#### jerzmacow

• Newbie
• Posts: 3
##### Crystal oscilators
« on: July 07, 2011, 08:32:58 pm »
First post! I've always wondered how 2 pin crystal oscillators worked, and for that matter what the difference is between the 4 pin and the 2 pin ones. This is a pretty common topic I would assume so if anybody has some good links that would work to. I looked on google but nothing I came up with was of much help.

Thank you!

p.s
For some reason "the meaning of life, the universe and everything" doesn't work for the authentication. I hope that's a bug.

#### Zero999

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##### Re: Crystal oscilators
« Reply #1 on: July 07, 2011, 08:50:28 pm »
The two pin components are not complete oscillators. They are crystals and need other components to make them oscillate. The four pin components are complete oscillators and don't need any additional components.

#### ejeffrey

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##### Re: Crystal oscilators
« Reply #2 on: July 07, 2011, 09:31:14 pm »
A 2-pin crystal is basically like a tuning fork.  If you bang it on something it will ring at a specific frequency, but die away eventually.  You can make an oscillator out of a tuning fork by putting a microphone on one side, and a speaker on the other.  Just like a PA system will squeal due to feedback if the microphone is next to the speaker, this system will oscillate.  Unlike the undisciplined feedback of the PA system, it only works at a single frequency very close to the natural frequency of the tuning fork.

A 4 pin crystal oscillator has essentially this circuit built in.  There is a little amplifier that amplifies the output from one terminal of the crystal and applies it to the other.  All of the components are set correctly so that you apply power and you get a clock out.

Smf