Jump to content
Sign in to follow this  
makro2

Accurate timing ( 0-500Hz +/- 5ppm)

Recommended Posts

I need accurate timing for my project. I'm going to use PIC16F88 (20MHz).

 

What is the best solution for external oscillator/clock, is there accurate crystals?

 

can i use SPG8651A  (selectable output crystal oscillator) for pics oscillator...

Share this post


Link to post
Share on other sites

The best way would be using LP configuration to draw a minimal current from the PIC's internal osc driver (although an external clock wiring will let the OSC2 pin unconnected, and no current will flow through it anyway).

 

Then, the simpliest and most accurate solution should be a crytal oscillator, with a frequency (let's call it Fq) equal to a power of 2 if u wanna use interrupts.

Therefore, you can use this subcircuit to drive a 74HC161, which will provide you with 4 selectable clock rates : Fq/2 , Fq/4, Fq/8, Fq/16.

 

Then, with a 4MHz oscillator, you can get a 500kHz frequency from pin12 (Q2) of the 74HC161.

 

This is a sure way to get many different clock sources from a cheap circuit (u can get a 74HC161 for less than half a buck !).

 

Another solution would be to use a 1MHz ext clock combined with a "divide by 2" subcirtcuit. But the number of device will reach the first I described, without as many rates (ie : five) as you could desire !

 

Don't think about ACCURATE clock sources neither with RC pairs, nor resonators.

I almost forgot : SPG8651A offers a 100ppm stability. Far away from your 5ppm needs !!!!

 

Nota Bene : I was talking n'bout CRYSTAL clock sources, cuz, as you said, you need 5ppm accuracy.

Share this post


Link to post
Share on other sites

Join the conversation

You are posting as a guest. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...