Alison,

On Sun, 8 May 2005 11:27:14 -0700 (PDT), Alison Lewis wrote:

>...<
> What may seem unusual in the board are TWO Caps, one
> for the initial input power and one for 5V after the
> regulator. (anyone else do this?)

Yes, but I'm a bit confused as to the sizes of them - C1 is a larger value than C2, and is upstream of the 
regulator so should be at least the same voltage rating, if not higher, but you're showing it physically 
smaller - this is unexpected, at least!  :-)

Further, you have these two "reservoir" capacitors (to provide/absorb energy to smooth over varying 
line/load), but no decoupling capacitors to stop oscillation.  As someone else said, you really need 0.1uF 
ceramics across the 0V and power close to the regulator and close to the PIC.

Since you have a 5V reservoir capacitor, you should also have a diode across the In and Out of the regulator 
(+ve on the In side), so that if the power drops and the input capacitor discharges before the output one, 
that the voltage on the regulator's Out pin doesn't go above that on the In pin (otherwise the regulator can 
be damaged).  In fact it can still be 1 diode-drop (0.6V) above it, but that's OK!

I don't like the 0V trace that connects to your Input header going "through" the resonator's centre pin - 
varying current in that trace might upset the PIC oscillator and gain or lose you clock cycles (or even stop 
the oscillator all together).  Better to run it separately if at all possible.

I don't understand what B1 and B2 are - looking again I suspect they are probably the power-in points, and I 
assume they will have wires soldered in directly - it's much neater to have these together if possible.  And 
please label them - you know what they are now, but when you get the soldering-iron out you don't want to have 
to deduce which is which from following the traces  :-)

Your "Extra Inputs" are actually 0V and 5V!

There are 4 orphaned holes on the left below the Input header and 6 between C2 and the PIC, for no obvious 
reason.

D6 (what happened to D1 to 5? :-) is awfully close to the PIC - if you are going to use a socket for the 
latter, a bit more space would be handy.

I notice a lot of unconnected pins on the PIC - make sure you set these to output in your software, as 
unconnected inputs can wreak havoc.

There you go, my random thoughts - have fun!  :-)

Cheers,




Howard Winter
St.Albans, England


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