How do you connect the collector of the transistor? For AVR to control the transistor, the emitter had to connected to ground or 0V of the AVR, then how you control the supply to the AVR?
I guess you're trying to do something like this:http://arduino.cc/forum/index.php/topic,105255.msg795853.html#msg795853
It's hard to tell, have a normal electrical drawings?If it the same, as in post reply #16 http://arduino.cc/forum/index.php/topic,105255.15.html ?
If power consumption is concern, I'd replace BJT with MOSFET, in current configuration, circuitry (referring to reply #16) drains about 2 mA just to keep arduino "on". Probably, more than 3 mA with higher input voltage 5V < Vin < 9V.http://ruggedcircuits.com/html/circuit__11.html In this circuit wasted current less than 0.1 mA, and you can make it even less setting higher resistors value 47 k to 100 k or 470 k.
I'm currently building a project that has no on/off switch and needs to power down if inactive. I'm doing it using the power down mode of the mcu, which reduces the current it takes to a fraction of a microamp (atmega328p). It's powered by a 9V battery, so to produce 5v I'm also using a low-dropout micropower regulator (MCP1702) which has a unloaded current draw of 2uA typical. A 9v alkaline battery has a capacity around 600mAh at low drain. So with about 3uA current drain, the theoretical battery life when the circuit is powered down is 200,000 hours, or about 22 years - much longer than the shelf life of the battery.A pushbutton connected to one of the external interrupt pins is used to wake it up and turn it on.
That's food for thought for sure, this whole circuit is redundant in that case