Custom built Arduino on a Breadboard With Add Pir Motion Sensor

[system]

Hi Every one!
My name is Metrik.
And I need some help on this project i am working on.
I am building a custom Arduino. and i am try to add a pir motion sensor to the Arduino so that when the PIR Sensor pick up something it turns the Arduino on and runs the program that is on the Arduino. but i have a on and off switch to. So if it is possible i want to put a switch on the PIR Sensor so i can trun that feature off when ever need. but also have a second switch that turns the Arduino on when the PIR Sensor has beed disabled.
Any help would be great.
Thanks Every One.

[system]

how are you going to determine when your arduino must be switched on? you have to have some kind of microcontroller running to check the values of the PIR sensor..it won't give results by itself

so you'll have to keep your arduino (or at least atmega328P here) running, or use (for example) an ATtiny to check the PIR sensor, and make it switch some kind of rellay that turns on the arduino power

[CrossRoads]

PIR's usually have open drain outputs.
Use that to pull a P-Channel Mosfet gate low, to source power to arduino.
Have arduino hold gate low once sketch starts until it is done doing whatever.
I Upload using Programmer (via ICSP) to ensure the program starts immediately and not wait for a bootloader to do its thing.

[system]

Thanks CrossRoads
Is there any way u can give me more detail in how to go about doing that. It would be great. I am new to the arduino. Thanks again.

[CrossRoads]

Here's the circuit I am envisioning.

PIR low output turns on the P-channel MOSFET, Vcc powers up the Arduino, Arduino holds the P-channel on until it is done doing whatever you are doing.