AVR-Chat

can someone please guide me with PCB designs? im trying to make my first PCB with eagle. also, i can't find a mega16 in the AVR library. and, i don't know anything about the "rules" in designing a good circuit board. thanks...
 
-jay

Graham Davies <YahooGroups@ecrostech.com> wrote:
--- In AVR-Chat@yahoogroups.com, "Phil" <phil1960us@y...> wrote:

> I find the eagle autorouter to be pretty dumb.

I would like to disagree with this, but agree with the general 
direction of the discussion.  I use Eagle and think that the 
autorouter is pretty good and darned good for the money. This is my 
methodology:

Small, double-sided boards with mixed through hole and surface mount. 
Draw schematic. Place components guided by airwires. SAVE. Autoroute 
with goal of 100%. Quit, don't save, re-open unrouted board. Try 
again, changing settings such as preferred direction on each layer. 
Repeat until autoroute is 100% or near, moving components if 
necessary. Note best directions. Starting with unrouted board, lay in 
ground, power and critical nets by hand, keeping to best directions 
on each layer. Autoroute from time to time, but always discard. Look 
for congestion and adjust placement and hand-laid traces to relieve. 
When satisfied, autoroute and save. Look for and fix stupid routes. 
Route any unrouted traces by hand. Look for other improvements as 
time permits. Fatten up ground as much as possible, perhaps using 
polygon floods. For best EMI performance, when the ground is laid in 
by hand you need to form a grid, not just a meandering wire, with 
apertures in the grid as small as possible. This provides multiple 
return paths for signals and greatly reduces emission of and 
succeptibility to EM interference. Of course, if things are really 
bad you need a full ground plane but at minimum you need a grid.

Graham.



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