arduino boot up button and shutdown mode on regulator
Unfortunately I can not open your schematic, but I have an improvement that will definitely make this thing work.

Have a look at this:







simulate this circuit &ndash; Schematic created using CircuitLab

where:


reg_shdwn is the regulator shutdown pin
atm_wake_me is the pin you use to wake up the ATMega
atm_keep_on is the pin you would use to keep the regulator on


When SW1 is pressed all three pins go high, C1 is charged at \$V_{cc}\$ and the micro turns on. If the user releases the button before that the ATMega managed to pull atm_keep_on high the whole system does not shutdown though, since the capacitor will need some time to discharge through R1. You should size R1 and C1 to have a time constant \$\tau\$ that allows your micro the time it needs to pull the pin high.

The downside is that you dissipate some power through R1 when the system is on, but of course the resistor can be sized to minimize this power, while still being smaller than the input resistance of the arduino and the reg_shdwn pin.

Since of course \$\tau=RC\$ we can make an example calculation to aid you. I'd say that for R1 you should choose somethin in the \$100\$k\$\Omega\$ range, let's say \$R1=470\$k\$\Omega\$. \$\tau\$ can be some \$100\$us, i.e. 100 clock cycles at 1MHz. This leads to \$C\approx22\$nF, a perfectly reasonable value.

As a side note, a \$470\$k\$\Omega\$ resistor would dissipate about 23uW if \$V_{cc}=3.3\$V.