>> Or, just the input series diode and hope for the best till monday. :)
>>
JA> I put a 4.7 ohm resistor on the input then a big cap (an electrolytic
JA> though so i should fix that with a diode as well to protect it from
JA> reverse polarity.) then my 7805, been running "flash an LED" now for a
JA> few months. Newer small 4cyl jobby though so i don't know if that will
JA> make a difference. On my input lines I used a resistor dividor network
JA> to bring the 12v down to 5 then I put a 10meg resistor from the junction
JA> to the pin. Microchip has an appnote for picking up zero crossings in
JA> mains wiring where they use ~12meg worth of resistance connected
JA> directly to mains (110V) and let the diode in the PIC handle the currents.

Using a bridge rectifier in front of the 7805 and its caps may help ?

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