Crystal oscillator

[deepakrajchris]

Hi guys am new to this site .Plz help me out. . . . .i need the formula to calculate the frequency of oscillation for a crystal oscillator . . .Am using two capacitors valued 22pF directly connected to the oscillator pins of micro-controller At89c52. . .And the output is 12Mhz

 

[MrAl]

Hi,


The crystal is modeled as a large inductance and series and parallel capacitances. Adding the two external load capacitors complicates this quite a bit. But even without them, you have to know the equivalent internal inductance and capacitances in order to do this kind of calculation. These parameters would be estimated anyway so you would not be able to calculate the frequency too accurately if you did. At least not for a practical circuit like you are talking about.

In theory however you can do this. You can choose a typical inductance and capacitances and also add the two external capacitors as variable capacitors. You can then calculate the frequency. By making the two external caps variable, you can study the effects of changing the two capacitors and this will give you insight as to how these two caps really make the frequency change. Most likely when you go to use this crystal in a real life circuit however you wont see the actual frequency as calculated, but you will see a similar variation as the external caps are changed to other values or even eliminated.

It's still harder to see the frequency variation with temperature using various caps though even in theory.

 

[deepakrajchris]

First of all thanks a lot. . . . . . . . . . . for helping me out. . . . i need a lot of guidance like this. . . .

I need the formula for calculating theoretically only friend. . . . .

And i really need an important detailed explanation for how HT12e works. . . . i mean what is the internal operation. . .I studied the data sheet and i cant understand the internal operation. . . .In my project we use an joystick which is connected to the data lines of the encoder. So that the 4 lines are converted into single line and fed to the RF module. . .WHAT I REALLY NEED IS HOW THE 4 BIT DATA IS CONVERTED INTO SINGLE LINE.. . . . . .

 

[jpanhalt]

I have heard that the HT12e encoders and matching decoders are really just dedicated , pre-programmed microcontrollers. If that is the case, it is unlikely the code will be shared openly.

John

 

[deepakrajchris]

thanks a lot john. . . . .But i need the explanation for the internal block diagram for Ht12-e which is given in the datasheet

 

[davenn]

thanks a lot john. . . . .But i need the explanation for the internal block diagram for Ht12-e which is given in the datasheet

try contacting the manufacturer, but you may well find John's comments stand and they wont tell you about the inner workings

Dave