Basic use of crystal in microcontroller

Thanks John Popelish

A crystal is a very narrow band filter element based on the vibrational resonance of a slice of quartz and the fact that applying voltage to the slice causes it to change shape, and changing the shape by mechanical force generates voltage.

They are normally used as the frequency determining element in oscillator circuits, by connecting them in a signal loop, in series with a gain block. This combination generates an endless echo with a duration equal to the period of the quartz resonance. The stability of quartz oscillators is measured in parts per million, whereas the stability of oscillators based on RC time constants or inductor capacitor resonances is measured in percent.

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For instance, try putting these key words into the Google search box: [quartz crystal oscillator tutorial]

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"Endless echo". That's nice. :-)

Thanks. I think it is descriptive, too. Unlike RC oscillators, that generate each half cycle from scratch, just stacked after the previous half cycle, some energy from previous cycles goes back around to make up the next cycle in resonator oscillators. I think it is a distinction worth making.