Key press to switch on uC, timer to switch off power control of uC ?

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i want to use a uC for a remote control. I want to switch on the uC via a
keypress, start the programm inside and switch the complete power off after
a certain time (e.g. 30 seconds).

I thought it could be done in the following way:
Key press (it is coming from a 4 x 3 matrix keyboard) must enable delivering
power to uC, the uC starts up and a output PIN also must enable delivering
power (so the power remains when the key is released). After doing some
tasks and getting idle, the output PIN for power control changes and the
complete system is switched off.

Can someone suggest how to implement the power part or point me to schematic
for such a thing on the web ? Can i do it with 2 transistors ? Controlling
the output port and writing the software afterwards is not a big problem,
but i have no knowledge about analog circuits.



Re: Key press to switch on uC, timer to switch off power control of uC ? says...
Quoted text here. Click to load it
Most MCU's have some sort of sleep or low power mode that draws in the
microamp range, which is usually less current than the self discharge
rate of most modern cells.  It is a trivial matter to have say a PIC MCU
go to sleep after a period of time and wake on a button press.  


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