As you probertly know the 7805 is destined to get wery_hot as you are
dissipating ALOT of wattage

lets do a simple calculation
you are drawing 500mA in your circuit ...

12V - 5V  * 500mA = 3,5W - That's why you DO need a heatsink and why the
7805 can (and properly will) get wery hot.

Maybe 500mA is a bit "over calculated" but it shows the effect that the
power loss dissipation has on the regulator.

You could protect your circuit from over-voltage with a zener diode and a
resistor. (which shouldn't happen because the regulator has a shutdown unit
but  - you cant be to safe :)

You could also protect your circuit from over-current with a transistor.

Try measuring with your scope (if you have one) the Ripple voltage on the
output of the regulator when its pretty hot. try adding a large electrolytic
capacitor to reduce the ripple ... ripple can kill a pic ...

You could also use a Driver IC to supply the PIC if anything is killed it
would be the Driver IC

You could also add a 1K resistor to protect against overcurrent.

CHECK if you have reversed the supply pins ! ! - THIS WILL KILL THE PIC !

 Hope you will get some ideas from this.

Best Regards
lasse madsen

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