Minimize battery consumption on a 18F2550

[Fredrick]

Will this schematic work?

When u press a button the FET will switch on the 7805 and the PIC, and then I hold RA4 low as long I want the PIC to run.
The +BATT terminal is from a 9V battery and the datasheet says that RA4 can handle up to 14 volts if I have understand it right, so 9V on RA4 will be OK?

[pedja089]

It wont work. Because if PIC doesn't have power supply, current still can be drown from pin, and that will be probably enough to turn on fet. Even if RA4 is open drain, you can put more than VDD+0.6 on that pin. If you do this, you will damage input buffer.
So you need to to put transistor to bring down gate. Depending on P FET you use and battery voltage, maybe you need to put another resistor to create voltage divider for gate.
EDIT:

[aratti]

Using a voltage regulator introduce some complication. You will feed 9 volts to your inputs and this will demage your pic. You need to isolate in same way your pic (both input and output) see the attached suggestion. (remember that all the input must be pulled up)

Cheers

Al.

[Fredrick]

Will this work then?
PORTB are using internal weak-pullups, and I keep RA0 high as long as I want the PIC to run.

[aratti]

When the push button is open you feed 9 volts to the pic input. Place a diode on each input to stop this current flow.

Cheers

Al.

[Fredrick]

Does it look ok now?
I assume the standby current now will be 0uA when no button is pressed and the RA0 is not high?

[amgen]

the input to pic pins (9 volt) is limited by the 100K r and those pins should have redirect diodes (inside pic) that protects pic from overvoltage.
The opto will shutdown power or the r-c on fet gate can be made to time out (any time you set) but the power to pic then just reduces slowerly? ,,,but the brownout setting also will shut down pic before too low voltage makes program unfunctional ..
don