> http://www.juliankain.com/schematic_20050223.pdf
>
> Thanks a lot for any specific design or otherwise general advice any of 
> you may have to lend.

1) LM340 5V regulator would probably like a bit more "bulk" capacitance 
right at its output pin.  Add about 10uF.  The voltage rating should be at 
least 10V.

2) Add an anti-reversal diode (1N4001 or similar) where your power enters 
the board.  Yes you will need to compensate at least another 1V more input 
voltage to keep the regulator headroom but you won't be as likely to 
accidentally hook up power backwards...

3) Consider diode (ANODE at Vout, CATHODE at Vin) on the regulators to 
guarantee their outputs don't swing far from the input voltages.  This is 
more important if you end up adding a lot of output capacitance to the 
regulators.

4) The 20MHz xtal you have picked, am I to assume the ground connections you 
show are to ground the xtal's case?  If it isn't an xtal but really a 20MHz 
oscillator then you don't need C12 and C13 and you would only be connecting 
to the OSC-IN pin on the PIC.

5) I didn't spend a lot of time scrolling around to find out if you have 
seperate analog and digital grounds and if you are connecting them at a 
single point.  This helps to keep digital ground currents from making your 
analog grounds flinch and flail.

6) For your MAX232 you show 1uF caps.  If you are using polarized caps (but 
you show non-polarized caps so maybe this comment isn't necessary) observe 
the polarity of the C+ and C- terminals etc when connecting the capacitors.

Like I said in #5 I didn't spend a lot of time scrolling around to check 
connections.  My personal preference is for heirarchical schematics on 8.5 x 
11 sheets with the top sheet being a block diagram and each following sheet 
a small portion of the schematic, logically partitioned so that each sheet 
stands nearly on its own for viewing and debugging.  Just personal 
preference though...

Rob Young
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