If you are after a 1-chip oscillator, a PIC with a xtal wil give really exact frequencies AND xtal locked accuracy.

On the bottom of this page is simple C code with any PIC to make incredibly precise decimal frequencies;
http://www.romanblack.com/onesec/High_Acc_Timing.htm#decfreq

(0.00001Hz to 20KHz) on PIC 16F628A
(0.0001Hz to 50KHz) on PIC 16F628A
(note the 0.00001 Hz resolution!)

A few lines of code... Just beats a 555 and a drifty cap.

 

If you are after a 1-chip oscillator, a PIC with a xtal wil give really exact frequencies AND xtal locked accuracy.

On the bottom of this page is simple C code with any PIC to make incredibly precise decimal frequencies;
http://www.romanblack.com/onesec/High_Acc_Timing.htm#decfreq

(0.00001Hz to 20KHz) on PIC 16F628A
(0.0001Hz to 50KHz) on PIC 16F628A
(note the 0.00001 Hz resolution!)

A few lines of code... Just beats a 555 and a drifty cap.

very nice. and just to note, not all pic's run C

 

Don't these chips have the option for RC oscillators?

 

RC oscillators, ceramic resonators, crystal oscillators and internal oscillators.

Comes in all flavors.

 

Don't these chips have the option for RC oscillators?

Cheeky!

You could clock the PIC with a 555.

 

There is a crystal controlled 555 circuit schematic floating around here in another thread somewhere. I suspect the OP is trying to make a PWM controller for a high voltage circuit, which is not a violation of ToS. If so the exact methodology is probably not critical, just what ever is easiest to cobble together.

I'm afraid I'm not being a very good moderator in this thread. I seem to want to steer it off topic when I should know better.

 

There is a crystal controlled 555 circuit schematic floating around here in another thread somewhere. I suspect the OP is trying to make a PWM controller for a high voltage circuit, which is not a violation of ToS. If so the exact methodology is probably not critical, just what ever is easiest to cobble together.

I'm afraid I'm not being a very good moderator in this thread. I seem to want to steer it off topic when I should know better.

its all good Bill.
its actually all low voltage stuff and the final stage is the opto (from the other thread, etc). a PIC would reduce my IC count down to two (currently three on my bboard, two 8's and one 14).

i have used electrolytic caps in the past for fixed freq out of the 555, and the aging drift for that module was acceptable. this new application some drift is still acceptable, etc. i was just more curious to know some more about the cap types when used in RC timing circuits, etc.

thanks all for the replies, i think this one is done.