Crystal Oscillator?

[Marks256]

I am in diar need of a crystal oscillator curcuit! I would like to make an oscillator out of a 3.xxxxxxx crystal. The one i have right now is 3.588513mhz, but i also have a 3.7x, and a 3.4x, etc. I would like one that worked with a good majority of these. I don't have very many parts. I have quite a few 2n3604 transistors, and some reistors, and cap's. Does anyone have a curcuit? Would it run at 5v? I need this to be TTL compatable.

It would be cooler if i could make one on my own. But i don't know how to hook one up? I send power through it, but i get nothing on the other side? How do you use crystals? I hope i am refering to the crystal properly, it is a little two-pined thing that is about 1.25cm high. Yah, i think that is a crystal. Please help.

 

[Hero999]

http://www.google.com/search?num=10...s=en&q=crystal+oscillator+circuit&btnG=Search

http://www.geocities.com/SiliconValley/Peaks/3938/uexosc.htm

**broken link removed**

 

[Marks256]

Yes, unfortunatly i have came across the first two on my own. I think i have enough components now to build the third one on the second link. Would these be stable sorces of a clock?

 

[Papabravo]

Stable? Yes and no. You need to specify what your requirements are. What are you using this oscilllator for?

If stable means will the oscillator start and oscillate in the vacinity of 4 MHz. then yes. If stable means that the frequency will vary no more than 0.1% over time, temperature, and VCC, then probably not.

 

[Marks256]

I need it as a clock for my Z80(cpu), and a few other digital applications(when i get to them...). How does a crystal work? How do you hook one up? What does "Serial resonance" mean? What about "Parallel resonance"?

 

[Papabravo]

Crystals are AC devices. They are modeled as a capacitor in parallel with a resistor, an inductor, and a capacitor in series. They have a property called resonance which enhances the energy at certain frequencies and attenuates all others. Crystals have two resonant frequencies called "series" and "parallel". Manufacturerrs normally construct them to prefer one mode over the other.

If you go to a manufacturers website you can find application notes and turotial information in abundance.

 

[RadioRon]

I need it as a clock for my Z80(cpu), and a few other digital applications(when i get to them...). How does a crystal work? How do you hook one up? What does "Serial resonance" mean? What about "Parallel resonance"?

I fear that these questions are too big to answer on a bulletin board, so you may have to refer to a text book on this. I've got a few books where the whole book is required to answer these questions. My favorite is "Crystal Oscillator Circuits" Robert J Matthys, Krieger Publishing Company, Malabar, FL, 1992. I got my copy through Amazon I think.

A crystal is a piece of pure quartz rock that has the amazing behavior of being piezoelectric. This means that if you apply a voltage to the crystal, it vibrates a tiny bit and that vibration happens at a very specific frequency that depends on how the rock has been sliced. Oscillators take advantage of this behavior by putting the rock into a circuit that continously tickles it at the same frequency that it has been cut to vibrate at. This is a crystal oscillator.

Resonance occurs when you put energy into a structure that wants to vibrate at a specific frequency. Like, when you blow into a trumpet it will give you a specific note. This is done by "resonating" the air chamber inside it to a specific size using the player's controls. In electricity, we get resonance in AC circuits when we have some capacitive reactance coupled to some inductive reactance that happens to be equal to the capacitive reactance. The electrical energy introduced to them is traded back and forth between the capacitor and the inductor as their electric and magnetic fields build up and then collapse back and forth. This tends to happen very vigourously and with high currents because there is very little resistance in the way of this trading.

Crystals resonate mechanically, that is the crystalline lattice vibrates. If you attach wires to two sides of the rock, you actually get tiny amounts of AC voltage coming out of the crystal, which is the other way that a rock is piezoelectric.

 

[Marks256]

Ok, so how would i hook one up to a circuit? Or, how would i amplify that resonance?

 

[RadioRon]

Ok, so how would i hook one up to a circuit? Or, how would i amplify that resonance?

You insert the crystal into a crystal oscillator circuit. There are many of these of different types, too many to describe here. Simplest approach is to use the common inverter amplifier configuration used in almost all processors. here's one reference:

http://www.cirrus.com/en/pubs/appNote/an33.pdf#search='crystal%20oscillator%2074hcu04'

 

[Marks256]

Thanks, i will print it off tommorrow and read it.

 

[RadioRon]

This reference might be a bit better:
https://www.fairchildsemi.com/an/AN/AN-340.pdf#page=1


If you build your own crystal oscillator using an HCMOS gate, use this part: 74HCU04. That U in the number is important. It means "unbuffered". They make this one special for jobs like oscillators where the lack of an internal buffer helps reduce the propagation delay through the gate and increases the oscillation range of the part as well as perhaps increasing the start-up behavior too. Of course, if you don't have that part, don't sweat it, you will still likely get it to work with any kind of HCMOS gate configured as a simple inverter.

 

[Marks256]

I was wondering, is there a curcuit out there that will allow a variable clock from about 1hz to 4mhz?

 

[RadioRon]

Such a circuit is possible, but will be quite complicated. I would use a two-loop heterodyne frequency synthesizer to build such a thing.

 

[Papabravo]

If you feel adventurous you can google for phase locked loops. This circuit consists of three parts and has some pretty hairy math underneath. Don't worry about the math part for now.

The three parts are:
1- A phase comparator circuit whose output is proportional to the phase difference between two signals.
2- A VCO or voltage controlled oscillator.
3- A loop filter

There may also be a digital divider that divides the output frequency down to provide one of the inputs to the phase comparator. Break this circuit down, study the parts one at a time, then put it all back together. You'll be glad you did.

 

[Marks256]

Ok, i don't need complicated right now. I am still trying to grasp a few things yet.

 

[StopGo]

I'm thinking you just need a low hassle clock thats going to get the job done for your micro project yer ? Maybe what your looking for is a crystal module, these don't need any external components (bar the odd ceramic cap) and are great for driving all sorts of high speed digital circuits.

Check these out ...
**broken link removed**

V+, GND, and Output

 

[Marks256]

Yes, i know what those are. Aren't they called "Crystal Oscillators"? I think they are. They are pretty much a whole circuit in a can. I have a few of these, but i just don't have one that is slow enough. I only have 15-20mhz modules. Soon, though, i will be ordering a few components from jameco(www.jameco.com). I will be getting a few of these and a bunch of other things too. Thanks though!