Re: PIC power supply circuit
The 7805 regulator is as good as any other voltage regulator (who cares about its age) and it can be easily used in automotive applications ..
Just take certain precautions (as you would do with other voltage regulators) and you should be fine ..
First of all, you need something to take care about overvoltage spikes, and a small resistor (I’d say Rin~4.7Ohm or PTC) together with an RF-choke (~100uH) followed by a Zener diode (or Transient Voltage Suppressor) should do just that ..
Use C1≥220uF and C3≥10uF, they also have to be accompanied by 100nF at each side ..
Then install a couple of 100nF somewhere in the vicinity of your PIC ..
In addition, if there is anything else in your circuit that may draw some current, consider a heatsink for the 7805 voltage regulator ..
Rgds,
IanP