M
Michael Noone
- Jan 1, 1970
- 0
Hi - I'm working on a board that I need to save absolutely every last
square mm of space on. Normally I just use a crystal and two capacitors as
a clock source for a microcontroller - but that actually takes up a good
deal of board space. I looked at using all surface mount parts - but in the
end - such parts will probabaly take up nearly as much board space as the
AVR itself! (for some odd reason I couldn't find any small surface mount
crystals)
So then I've been looking at using through hole crystals and probabaly
surface mount caps - the crystal I'm looking at is 1.1mm pitch, so it would
take up very little board space - definitely an improvement over the
surface mount crystals (the ones I was looking at were 3x5mm)
But then I was looking in Eagle (a pcb design program) to see if they
already had this crystal in the built in library. The only cylinder type
had something very odd in it - there was a circle in the middle of the part
showing the outline of the crystal. Then nearly tangent to the center
circle was the two pads for the crystal. So it looked something like oOo if
you can follow my crude drawing. What this means to me is that for some
reason they felt the pins coming from the crystal needed to be seperated.
This pretty much gets rid of the benefit of using the cylinder type
crystal. Does anybody know why it would be drawn like this? Or would it be
OK for me to have the pads with 1.1mm pitch? Are there any other really
small 20Mhz clock sources?
Thanks!
-Michael J. Noone
square mm of space on. Normally I just use a crystal and two capacitors as
a clock source for a microcontroller - but that actually takes up a good
deal of board space. I looked at using all surface mount parts - but in the
end - such parts will probabaly take up nearly as much board space as the
AVR itself! (for some odd reason I couldn't find any small surface mount
crystals)
So then I've been looking at using through hole crystals and probabaly
surface mount caps - the crystal I'm looking at is 1.1mm pitch, so it would
take up very little board space - definitely an improvement over the
surface mount crystals (the ones I was looking at were 3x5mm)
But then I was looking in Eagle (a pcb design program) to see if they
already had this crystal in the built in library. The only cylinder type
had something very odd in it - there was a circle in the middle of the part
showing the outline of the crystal. Then nearly tangent to the center
circle was the two pads for the crystal. So it looked something like oOo if
you can follow my crude drawing. What this means to me is that for some
reason they felt the pins coming from the crystal needed to be seperated.
This pretty much gets rid of the benefit of using the cylinder type
crystal. Does anybody know why it would be drawn like this? Or would it be
OK for me to have the pads with 1.1mm pitch? Are there any other really
small 20Mhz clock sources?
Thanks!
-Michael J. Noone