AVR-Chat

Thank you all kindly for your suggestions, I've made a few changes to
the overall circuit layout:

1W 5.1v Zeners added to 12v digital inputs - I had considered doing
this earlier, but made the assumption - without calculation - that a
1K resistor "should" provide all the input protection I need, but
better safe than sorry!

max v=60
I = 60/5000 = 12mA
W = 60x0.012 = 720 mW dissapated by the Zener in a worst case scenario

I think the original calculation for the 1k was for a 5.0v VREF, when
you factor a spike of 60v into the equation that is clearly not
adequate - thanks for the pickup!

This circuit is particularly for a diesel application, and although
there would be some feedback floating around from the likes of starter
solenoids and inductive fans - at least there is no ignition feedback
to worry about!

Supply rails are already well protected via MOV, Polyfuse and
Zener/Diode arrays (I wouldn't trust a 7805 to do this job by itself
any farther than I could throw it! :)

ADC4 --> Moved to ADC2 for better resolution

AREF has been modified to use decoupling cap & internally source AVCC
for AREF

Now I just have to wrap my head around good PCB design rules :)