PIC18 not working when wiring 30pf capacitors of cristal resonator to ground

Question

I'm using pic18 with external oscillator 16MHZ 16M HZ HC-49S Crystal Oscillator with two 30PF capacitors

configuration OSC = HS

using breadboard, when wiring the capacitors to ground the pic stop working, but when letting them in open circuit (just wire one side to PIC, other side stay open) the PIC work again.

but when removing the capacitors from the circuit, the PIC also not working

what explanation for this

There is probably enough picofarads in the breadboard to make it work, but when you add an extra 30pF it becomes too high a load? — KyranF, Oct 29 '14 at 07:06
Yes, indeed. with Picofarad magnitude! The pins in the breadboard capacitively couple to nearby pins. You really should not try to use 16MHz signals on a breadboard, it will hardly work even if you think it is. — KyranF, Oct 29 '14 at 07:14
Good old Dave Jones (a fellow Aussie!!) talks about it in his video maybe that will help you understand it: http://youtu.be/6GIscUsnlM0 — KyranF, Oct 29 '14 at 07:15
Yes, those white solderless breadboards have a significant amount of capacitance and inductance... more than a PCB. — MarkU, Oct 29 '14 at 07:15
@KyranF thanks a lot, by watching the video I can understand better — Lkaf Temravet, Oct 29 '14 at 07:35
It would help if you read this question and updated yours to say whether it is a crystal or resonator. — David, Oct 29 '14 at 07:53
so in conclusion, go for 18pF capacitors or even less, and it may work better. — KyranF, Oct 29 '14 at 07:53
@KyranF I don't want to edit the question and change what the author means unless I'm sure. — David, Oct 29 '14 at 10:02

score 1 · Accepted Answer · answered Oct 30 '14 at 19:54

30pF seems a bit high. The datasheet states that for 20MHz (which is near your 16MHz) capacitors of 15pF are advised. Furthermore the (paracitic) capacitance of your breadboard is probably also pretty large (in the order of some pF).

So I suggest to try 15pF, or maybe even 12pF or so.

PIC18 not working when wiring 30pf capacitors of cristal resonator to ground

1 Answers1