Hello,
The small caps are usually used to prevent the crystal from oscillating
in the overtone
mode and are usually in the 10's of pF range (value depends on crystal
characteristics).
0.1uF just shorted out even the crystal's fundamental to GND and so no
oscillation.
Hope this helps. Jeff
At 11:58 PM 10/20/03 -0700, David Shoemaker wrote:
DOH,
those of you on the vector list will have already seen this. Sent
it to the wrong list.
For those of you not on
vectorlist:
While building up the two beta 9100 keyboard
wedge boards I realized I didn't have any 22pf caps. So I tossed a
pair of 100pf caps onto my breadboard of the circuit and everything
worked great.
Then I went to build the perfboard version and
realized I only had two of the 100pf caps and as I wanted to leave the
breadboard version intact for now so I grabbed a pair of .1uf
caps.
Hooked everything up and it didn't
work.
So I checked everything twice more and still no
go. Got to wondering if maybe the value of those caps is really
important and realized I have NO idea how to spec them nor even what they
do.
So can anyone enlighten me?
I have seen circuits use 18pf, 22pf and 27pf
for the crystal caps. The 100pfs do work, but I wonder now if I
just got lucky.
Also which should I use, simple ceramic disc or
the Monolithic ceramic disc?
David