Minimize battery consumption on a 18F2550

[Fredrick]

Thank you for your replay.

How do I do that and what parts do I need?
Do you have an example or schematic?

I can suggest to switch off everything when not used, so you will have no power drain. When you press any button to activate the proper command, you will switch on the system via a small fet activated with an array of diodes so that any button will switch on the fet. Your pic as activated will retain the fet on for all the time necessary to process the comand then it will switch off the fet again.

Cheers

Al.

[aratti]

Something like this should be a good starting point.

Cheers

Al.

[Fredrick]

Thanx
Can it also be done with a N-ch FET like the 2N7000 in some way?

[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.