Crystal oscillator

[mactack]

Hello,

I'm looking for a crystal oscillator (I'm building a digital clock). Would this one do: **broken link removed**

What capacitors should I use, 36pF ?


Thanks

 

[mramos1]

Hello,

I'm looking for a crystal oscillator (I'm building a digital clock). Would this one do: **broken link removed**

What capacitors should I use, 36pF ?

Is this the crystal to drive a microcontroller? Can you provide more details on the digital clock?

 

[mactack]

yes, it'll be to drive the microcontroller (a pic16f690). The clock is a binary clock (each digit displayed in binary) with 13 leds and 2 push buttons.

I tried using the internal clock but it's way off and from what I understand, the internal clock depends on voltage, temperature, ... anyway.

 

[mramos1]

Most of the datasheets will give you cap values for the Mhz/Khz crystals. Just check the datasheet.

 

[BeeBop]

Hi,

What capacitors should I use, 36pF ?

I believe what you want it Load Capacitance, which is given on your data sheet as 18pF

 

[mactack]

Hi,

I believe what you want it Load Capacitance, which is given on your data sheet as 18pF

Ah, I thought I had read somewhere it should be a little under twice the load capacitance...

What is the difference between a crystal and an oscillator? The oscillator includes the capacitors?

 

[kchriste]

What is the difference between a crystal and an oscillator? The oscillator includes the capacitors?

The oscillator contains an amplifier/transistor. The crystal provides a feedback path to make the amplifier/transistor scream at a set frequency.
Your pic16f690 has this amplifier built in and the datasheet specifies the types of crystals and caps you should use.

 

[BeeBop]

Ah, I thought I had read somewhere it should be a little under twice the load capacitance...

I only made that suggestion because 18pF looks close to what has always worked for me. On any pic I have had good luck with 15 or 20 pF caps, and I never go through all the calculations, etc, which you find in the PIC data sheets. 36pF seemed a little high, but it will probably work too.