# More Oscillator Related than Frequency it produces.

Discussion in 'General Electronics Chat' started by cjdelphi, Feb 1, 2011.

1. ### cjdelphi Thread Starter New Member

Mar 26, 2009
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No matter how much I read about a crystal Oscillator there's something I'm just not clicking on here.. for the more common ones we have 2 pins, the more expensive one have 3 pins (which to me makes more sense but...)

For simplicity's sake, you're able to cut a crystal which has a resonating frequency of 100hz , the idea is to pass an oscillating frequency (Square Wave Off/On 0/5v) so would you have to build an oscillator to generate an AC signal to feed into the Crystal Oscillator? then what?.

The 2 Pins, you send voltage in on say Pin 1? and out pops the Voltage on Pin 2? or how does this work? what am i missing? apply 5v, if 5v pops out the other side, it hits on exactly 100hz pulses?

I don't get it.. how's a 2 pin Crystal work in a circuit? (yes seen plenty of circuits with crystal's used, but I don't understand why they work...)

2. ### davebee Well-Known Member

Oct 22, 2008
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If you're referring to two pin crystals, then they are probably not oscillators; they are just slices of quartz with a metal plates pressed against two sides with wires brought from the metal plates to outside the can.

Three or four pin metal cans are more likely the complete oscillators that you're referring to. They contain a crystal device in a small oscillator circuit with the output of the oscillator brought outside the can.

If you have a Dremel with a cutoff wheel and an old PC motherboard, see if you can find each of these devices on the motherboard and use the Dremel to carefully cut the cans open.

You should be able to see the crystal itself inside a crystal can, and a tiny surface-mounted oscillator circuit inside the oscillator can.

3. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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719
As stated, the thin oval 2 pin crystals are just that - crystals.

The 3 pin epoxy encapsulated are often ceramic resonators, with integral capacitors.

The 4 pin rectangle "crystals" are comprised of the crystal in addition to the oscillator circuit, capacitors, etc.

The latter two are "plug and play" type, while the standalone crystal needs capacitors to set it's mode of operation (serial or parallel), in addition to loading capacitors on each pin, with an external feedback circuit to keep the oscillations going.

Feb 24, 2006
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